]> git.sesse.net Git - nageru/blobdiff - flow.cpp
Start parametrizing the operating points for DIS.
[nageru] / flow.cpp
index 6861fa40739d8952a608364d14f1a370f43dac16..95bb1547b64b1095559632bd798a5f5fc9c8fe81 100644 (file)
--- a/flow.cpp
+++ b/flow.cpp
@@ -15,6 +15,7 @@
 #include <stdio.h>
 #include <unistd.h>
 
+#include "flow.h"
 #include "gpu_timers.h"
 #include "util.h"
 
@@ -31,12 +32,6 @@ using namespace std;
 
 SDL_Window *window;
 
-// Operating point 3 (10 Hz on CPU, excluding preprocessing).
-constexpr float patch_overlap_ratio = 0.75f;
-constexpr unsigned coarsest_level = 5;
-constexpr unsigned finest_level = 1;
-constexpr unsigned patch_size_pixels = 12;
-
 // Weighting constants for the different parts of the variational refinement.
 // These don't correspond 1:1 to the values given in the DIS paper,
 // since we have different normalizations and ranges in some cases.
@@ -44,7 +39,7 @@ constexpr unsigned patch_size_pixels = 12;
 // although the error (EPE) seems to be fairly insensitive to the precise values.
 // Only the relative values matter, so we fix alpha (the smoothness constant)
 // at unity and tweak the others.
-float vr_alpha = 1.0f, vr_delta = 0.25f, vr_gamma = 0.25f;
+static float vr_alpha = 1.0f, vr_delta = 0.25f, vr_gamma = 0.25f;
 
 bool enable_timing = true;
 bool detailed_timing = false;
@@ -235,36 +230,6 @@ void bind_sampler(GLuint program, GLint location, GLuint texture_unit, GLuint te
        glProgramUniform1i(program, location, texture_unit);
 }
 
-// A class that caches FBOs that render to a given set of textures.
-// It never frees anything, so it is only suitable for rendering to
-// the same (small) set of textures over and over again.
-template<size_t num_elements>
-class PersistentFBOSet {
-public:
-       void render_to(const array<GLuint, num_elements> &textures);
-
-       // Convenience wrappers.
-       void render_to(GLuint texture0) {
-               render_to({{texture0}});
-       }
-
-       void render_to(GLuint texture0, GLuint texture1) {
-               render_to({{texture0, texture1}});
-       }
-
-       void render_to(GLuint texture0, GLuint texture1, GLuint texture2) {
-               render_to({{texture0, texture1, texture2}});
-       }
-
-       void render_to(GLuint texture0, GLuint texture1, GLuint texture2, GLuint texture3) {
-               render_to({{texture0, texture1, texture2, texture3}});
-       }
-
-private:
-       // TODO: Delete these on destruction.
-       map<array<GLuint, num_elements>, GLuint> fbos;
-};
-
 template<size_t num_elements>
 void PersistentFBOSet<num_elements>::render_to(const array<GLuint, num_elements> &textures)
 {
@@ -287,34 +252,6 @@ void PersistentFBOSet<num_elements>::render_to(const array<GLuint, num_elements>
        glBindFramebuffer(GL_FRAMEBUFFER, fbo);
 }
 
-// Same, but with a depth texture.
-template<size_t num_elements>
-class PersistentFBOSetWithDepth {
-public:
-       void render_to(GLuint depth_rb, const array<GLuint, num_elements> &textures);
-
-       // Convenience wrappers.
-       void render_to(GLuint depth_rb, GLuint texture0) {
-               render_to(depth_rb, {{texture0}});
-       }
-
-       void render_to(GLuint depth_rb, GLuint texture0, GLuint texture1) {
-               render_to(depth_rb, {{texture0, texture1}});
-       }
-
-       void render_to(GLuint depth_rb, GLuint texture0, GLuint texture1, GLuint texture2) {
-               render_to(depth_rb, {{texture0, texture1, texture2}});
-       }
-
-       void render_to(GLuint depth_rb, GLuint texture0, GLuint texture1, GLuint texture2, GLuint texture3) {
-               render_to(depth_rb, {{texture0, texture1, texture2, texture3}});
-       }
-
-private:
-       // TODO: Delete these on destruction.
-       map<pair<GLuint, array<GLuint, num_elements>>, GLuint> fbos;
-};
-
 template<size_t num_elements>
 void PersistentFBOSetWithDepth<num_elements>::render_to(GLuint depth_rb, const array<GLuint, num_elements> &textures)
 {
@@ -340,22 +277,6 @@ void PersistentFBOSetWithDepth<num_elements>::render_to(GLuint depth_rb, const a
        glBindFramebuffer(GL_FRAMEBUFFER, fbo);
 }
 
-// Convert RGB to grayscale, using Rec. 709 coefficients.
-class GrayscaleConversion {
-public:
-       GrayscaleConversion();
-       void exec(GLint tex, GLint gray_tex, int width, int height);
-
-private:
-       PersistentFBOSet<1> fbos;
-       GLuint gray_vs_obj;
-       GLuint gray_fs_obj;
-       GLuint gray_program;
-       GLuint gray_vao;
-
-       GLuint uniform_tex;
-};
-
 GrayscaleConversion::GrayscaleConversion()
 {
        gray_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
@@ -373,7 +294,7 @@ GrayscaleConversion::GrayscaleConversion()
        uniform_tex = glGetUniformLocation(gray_program, "tex");
 }
 
-void GrayscaleConversion::exec(GLint tex, GLint gray_tex, int width, int height)
+void GrayscaleConversion::exec(GLint tex, GLint gray_tex, int width, int height, int num_layers)
 {
        glUseProgram(gray_program);
        bind_sampler(gray_program, uniform_tex, 0, tex, nearest_sampler);
@@ -382,31 +303,9 @@ void GrayscaleConversion::exec(GLint tex, GLint gray_tex, int width, int height)
        fbos.render_to(gray_tex);
        glBindVertexArray(gray_vao);
        glDisable(GL_BLEND);
-       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, num_layers);
 }
 
-// Compute gradients in every point, used for the motion search.
-// The DIS paper doesn't actually mention how these are computed,
-// but seemingly, a 3x3 Sobel operator is used here (at least in
-// later versions of the code), while a [1 -8 0 8 -1] kernel is
-// used for all the derivatives in the variational refinement part
-// (which borrows code from DeepFlow). This is inconsistent,
-// but I guess we're better off with staying with the original
-// decisions until we actually know having different ones would be better.
-class Sobel {
-public:
-       Sobel();
-       void exec(GLint tex0_view, GLint grad0_tex, int level_width, int level_height);
-
-private:
-       PersistentFBOSet<1> fbos;
-       GLuint sobel_vs_obj;
-       GLuint sobel_fs_obj;
-       GLuint sobel_program;
-
-       GLuint uniform_tex;
-};
-
 Sobel::Sobel()
 {
        sobel_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
@@ -416,34 +315,17 @@ Sobel::Sobel()
        uniform_tex = glGetUniformLocation(sobel_program, "tex");
 }
 
-void Sobel::exec(GLint tex0_view, GLint grad0_tex, int level_width, int level_height)
+void Sobel::exec(GLint tex_view, GLint grad_tex, int level_width, int level_height, int num_layers)
 {
        glUseProgram(sobel_program);
-       bind_sampler(sobel_program, uniform_tex, 0, tex0_view, nearest_sampler);
+       bind_sampler(sobel_program, uniform_tex, 0, tex_view, nearest_sampler);
 
        glViewport(0, 0, level_width, level_height);
-       fbos.render_to(grad0_tex);
+       fbos.render_to(grad_tex);
        glDisable(GL_BLEND);
-       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, num_layers);
 }
 
-// Motion search to find the initial flow. See motion_search.frag for documentation.
-class MotionSearch {
-public:
-       MotionSearch();
-       void exec(GLuint tex0_view, GLuint tex1_view, GLuint grad0_tex, GLuint flow_tex, GLuint flow_out_tex, int level_width, int level_height, int prev_level_width, int prev_level_height, int width_patches, int height_patches);
-
-private:
-       PersistentFBOSet<1> fbos;
-
-       GLuint motion_vs_obj;
-       GLuint motion_fs_obj;
-       GLuint motion_search_program;
-
-       GLuint uniform_inv_image_size, uniform_inv_prev_level_size, uniform_out_flow_size;
-       GLuint uniform_image1_tex, uniform_grad0_tex, uniform_flow_tex;
-};
-
 MotionSearch::MotionSearch()
 {
        motion_vs_obj = compile_shader(read_file("motion_search.vert"), GL_VERTEX_SHADER);
@@ -453,18 +335,18 @@ MotionSearch::MotionSearch()
        uniform_inv_image_size = glGetUniformLocation(motion_search_program, "inv_image_size");
        uniform_inv_prev_level_size = glGetUniformLocation(motion_search_program, "inv_prev_level_size");
        uniform_out_flow_size = glGetUniformLocation(motion_search_program, "out_flow_size");
-       uniform_image1_tex = glGetUniformLocation(motion_search_program, "image1_tex");
-       uniform_grad0_tex = glGetUniformLocation(motion_search_program, "grad0_tex");
+       uniform_image_tex = glGetUniformLocation(motion_search_program, "image_tex");
+       uniform_grad_tex = glGetUniformLocation(motion_search_program, "grad_tex");
        uniform_flow_tex = glGetUniformLocation(motion_search_program, "flow_tex");
 }
 
-void MotionSearch::exec(GLuint tex0_view, GLuint tex1_view, GLuint grad0_tex, GLuint flow_tex, GLuint flow_out_tex, int level_width, int level_height, int prev_level_width, int prev_level_height, int width_patches, int height_patches)
+void MotionSearch::exec(GLuint tex_view, GLuint grad_tex, GLuint flow_tex, GLuint flow_out_tex, int level_width, int level_height, int prev_level_width, int prev_level_height, int width_patches, int height_patches, int num_layers)
 {
        glUseProgram(motion_search_program);
 
-       bind_sampler(motion_search_program, uniform_image1_tex, 1, tex1_view, linear_sampler);
-       bind_sampler(motion_search_program, uniform_grad0_tex, 2, grad0_tex, nearest_sampler);
-       bind_sampler(motion_search_program, uniform_flow_tex, 3, flow_tex, linear_sampler);
+       bind_sampler(motion_search_program, uniform_image_tex, 0, tex_view, linear_sampler);
+       bind_sampler(motion_search_program, uniform_grad_tex, 1, grad_tex, nearest_sampler);
+       bind_sampler(motion_search_program, uniform_flow_tex, 2, flow_tex, linear_sampler);
 
        glProgramUniform2f(motion_search_program, uniform_inv_image_size, 1.0f / level_width, 1.0f / level_height);
        glProgramUniform2f(motion_search_program, uniform_inv_prev_level_size, 1.0f / prev_level_width, 1.0f / prev_level_height);
@@ -472,56 +354,31 @@ void MotionSearch::exec(GLuint tex0_view, GLuint tex1_view, GLuint grad0_tex, GL
 
        glViewport(0, 0, width_patches, height_patches);
        fbos.render_to(flow_out_tex);
-       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, num_layers);
 }
 
-// Do “densification”, ie., upsampling of the flow patches to the flow field
-// (the same size as the image at this level). We draw one quad per patch
-// over its entire covered area (using instancing in the vertex shader),
-// and then weight the contributions in the pixel shader by post-warp difference.
-// This is equation (3) in the paper.
-//
-// We accumulate the flow vectors in the R/G channels (for u/v) and the total
-// weight in the B channel. Dividing R and G by B gives the normalized values.
-class Densify {
-public:
-       Densify();
-       void exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint dense_flow_tex, int level_width, int level_height, int width_patches, int height_patches);
-
-private:
-       PersistentFBOSet<1> fbos;
-
-       GLuint densify_vs_obj;
-       GLuint densify_fs_obj;
-       GLuint densify_program;
-
-       GLuint uniform_patch_size;
-       GLuint uniform_image0_tex, uniform_image1_tex, uniform_flow_tex;
-};
-
-Densify::Densify()
+Densify::Densify(const OperatingPoint &op)
+       : op(op)
 {
        densify_vs_obj = compile_shader(read_file("densify.vert"), GL_VERTEX_SHADER);
        densify_fs_obj = compile_shader(read_file("densify.frag"), GL_FRAGMENT_SHADER);
        densify_program = link_program(densify_vs_obj, densify_fs_obj);
 
        uniform_patch_size = glGetUniformLocation(densify_program, "patch_size");
-       uniform_image0_tex = glGetUniformLocation(densify_program, "image0_tex");
-       uniform_image1_tex = glGetUniformLocation(densify_program, "image1_tex");
+       uniform_image_tex = glGetUniformLocation(densify_program, "image_tex");
        uniform_flow_tex = glGetUniformLocation(densify_program, "flow_tex");
 }
 
-void Densify::exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint dense_flow_tex, int level_width, int level_height, int width_patches, int height_patches)
+void Densify::exec(GLuint tex_view, GLuint flow_tex, GLuint dense_flow_tex, int level_width, int level_height, int width_patches, int height_patches, int num_layers)
 {
        glUseProgram(densify_program);
 
-       bind_sampler(densify_program, uniform_image0_tex, 0, tex0_view, nearest_sampler);
-       bind_sampler(densify_program, uniform_image1_tex, 1, tex1_view, linear_sampler);
-       bind_sampler(densify_program, uniform_flow_tex, 2, flow_tex, nearest_sampler);
+       bind_sampler(densify_program, uniform_image_tex, 0, tex_view, linear_sampler);
+       bind_sampler(densify_program, uniform_flow_tex, 1, flow_tex, nearest_sampler);
 
        glProgramUniform2f(densify_program, uniform_patch_size,
-               float(patch_size_pixels) / level_width,
-               float(patch_size_pixels) / level_height);
+               float(op.patch_size_pixels) / level_width,
+               float(op.patch_size_pixels) / level_height);
 
        glViewport(0, 0, level_width, level_height);
        glEnable(GL_BLEND);
@@ -529,80 +386,32 @@ void Densify::exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint d
        fbos.render_to(dense_flow_tex);
        glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
        glClear(GL_COLOR_BUFFER_BIT);
-       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width_patches * height_patches);
+       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width_patches * height_patches * num_layers);
 }
 
-// Warp I_1 to I_w, and then compute the mean (I) and difference (I_t) of
-// I_0 and I_w. The prewarping is what enables us to solve the variational
-// flow for du,dv instead of u,v.
-//
-// Also calculates the normalized flow, ie. divides by z (this is needed because
-// Densify works by additive blending) and multiplies by the image size.
-//
-// See variational_refinement.txt for more information.
-class Prewarp {
-public:
-       Prewarp();
-       void exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint normalized_flow_tex, GLuint I_tex, GLuint I_t_tex, int level_width, int level_height);
-
-private:
-       PersistentFBOSet<3> fbos;
-
-       GLuint prewarp_vs_obj;
-       GLuint prewarp_fs_obj;
-       GLuint prewarp_program;
-
-       GLuint uniform_image0_tex, uniform_image1_tex, uniform_flow_tex;
-};
-
 Prewarp::Prewarp()
 {
        prewarp_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
        prewarp_fs_obj = compile_shader(read_file("prewarp.frag"), GL_FRAGMENT_SHADER);
        prewarp_program = link_program(prewarp_vs_obj, prewarp_fs_obj);
 
-       uniform_image0_tex = glGetUniformLocation(prewarp_program, "image0_tex");
-       uniform_image1_tex = glGetUniformLocation(prewarp_program, "image1_tex");
+       uniform_image_tex = glGetUniformLocation(prewarp_program, "image_tex");
        uniform_flow_tex = glGetUniformLocation(prewarp_program, "flow_tex");
 }
 
-void Prewarp::exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint I_tex, GLuint I_t_tex, GLuint normalized_flow_tex, int level_width, int level_height)
+void Prewarp::exec(GLuint tex_view, GLuint flow_tex, GLuint I_tex, GLuint I_t_tex, GLuint normalized_flow_tex, int level_width, int level_height, int num_layers)
 {
        glUseProgram(prewarp_program);
 
-       bind_sampler(prewarp_program, uniform_image0_tex, 0, tex0_view, nearest_sampler);
-       bind_sampler(prewarp_program, uniform_image1_tex, 1, tex1_view, linear_sampler);
-       bind_sampler(prewarp_program, uniform_flow_tex, 2, flow_tex, nearest_sampler);
+       bind_sampler(prewarp_program, uniform_image_tex, 0, tex_view, linear_sampler);
+       bind_sampler(prewarp_program, uniform_flow_tex, 1, flow_tex, nearest_sampler);
 
        glViewport(0, 0, level_width, level_height);
        glDisable(GL_BLEND);
        fbos.render_to(I_tex, I_t_tex, normalized_flow_tex);
-       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, num_layers);
 }
 
-// From I, calculate the partial derivatives I_x and I_y. We use a four-tap
-// central difference filter, since apparently, that's tradition (I haven't
-// measured quality versus a more normal 0.5 (I[x+1] - I[x-1]).)
-// The coefficients come from
-//
-//   https://en.wikipedia.org/wiki/Finite_difference_coefficient
-//
-// Also computes β_0, since it depends only on I_x and I_y.
-class Derivatives {
-public:
-       Derivatives();
-       void exec(GLuint input_tex, GLuint I_x_y_tex, GLuint beta_0_tex, int level_width, int level_height);
-
-private:
-       PersistentFBOSet<2> fbos;
-
-       GLuint derivatives_vs_obj;
-       GLuint derivatives_fs_obj;
-       GLuint derivatives_program;
-
-       GLuint uniform_tex;
-};
-
 Derivatives::Derivatives()
 {
        derivatives_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
@@ -612,7 +421,7 @@ Derivatives::Derivatives()
        uniform_tex = glGetUniformLocation(derivatives_program, "tex");
 }
 
-void Derivatives::exec(GLuint input_tex, GLuint I_x_y_tex, GLuint beta_0_tex, int level_width, int level_height)
+void Derivatives::exec(GLuint input_tex, GLuint I_x_y_tex, GLuint beta_0_tex, int level_width, int level_height, int num_layers)
 {
        glUseProgram(derivatives_program);
 
@@ -621,31 +430,9 @@ void Derivatives::exec(GLuint input_tex, GLuint I_x_y_tex, GLuint beta_0_tex, in
        glViewport(0, 0, level_width, level_height);
        glDisable(GL_BLEND);
        fbos.render_to(I_x_y_tex, beta_0_tex);
-       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, num_layers);
 }
 
-// Calculate the diffusivity for each pixels, g(x,y). Smoothness (s) will
-// be calculated in the shaders on-the-fly by sampling in-between two
-// neighboring g(x,y) pixels, plus a border tweak to make sure we get
-// zero smoothness at the border.
-//
-// See variational_refinement.txt for more information.
-class ComputeDiffusivity {
-public:
-       ComputeDiffusivity();
-       void exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint diffusivity_tex, int level_width, int level_height, bool zero_diff_flow);
-
-private:
-       PersistentFBOSet<1> fbos;
-
-       GLuint diffusivity_vs_obj;
-       GLuint diffusivity_fs_obj;
-       GLuint diffusivity_program;
-
-       GLuint uniform_flow_tex, uniform_diff_flow_tex;
-       GLuint uniform_alpha, uniform_zero_diff_flow;
-};
-
 ComputeDiffusivity::ComputeDiffusivity()
 {
        diffusivity_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
@@ -658,7 +445,7 @@ ComputeDiffusivity::ComputeDiffusivity()
        uniform_zero_diff_flow = glGetUniformLocation(diffusivity_program, "zero_diff_flow");
 }
 
-void ComputeDiffusivity::exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint diffusivity_tex, int level_width, int level_height, bool zero_diff_flow)
+void ComputeDiffusivity::exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint diffusivity_tex, int level_width, int level_height, bool zero_diff_flow, int num_layers)
 {
        glUseProgram(diffusivity_program);
 
@@ -671,47 +458,9 @@ void ComputeDiffusivity::exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint diff
 
        glDisable(GL_BLEND);
        fbos.render_to(diffusivity_tex);
-       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, num_layers);
 }
 
-// Set up the equations set (two equations in two unknowns, per pixel).
-// We store five floats; the three non-redundant elements of the 2x2 matrix (A)
-// as 32-bit floats, and the two elements on the right-hand side (b) as 16-bit
-// floats. (Actually, we store the inverse of the diagonal elements, because
-// we only ever need to divide by them.) This fits into four u32 values;
-// R, G, B for the matrix (the last element is symmetric) and A for the two b values.
-// All the values of the energy term (E_I, E_G, E_S), except the smoothness
-// terms that depend on other pixels, are calculated in one pass.
-//
-// The equation set is split in two; one contains only the pixels needed for
-// the red pass, and one only for the black pass (see sor.frag). This reduces
-// the amount of data the SOR shader has to pull in, at the cost of some
-// complexity when the equation texture ends up with half the size and we need
-// to adjust texture coordinates.  The contraction is done along the horizontal
-// axis, so that on even rows (0, 2, 4, ...), the “red” texture will contain
-// pixels 0, 2, 4, 6, etc., and on odd rows 1, 3, 5, etc..
-//
-// See variational_refinement.txt for more information about the actual
-// equations in use.
-class SetupEquations {
-public:
-       SetupEquations();
-       void exec(GLuint I_x_y_tex, GLuint I_t_tex, GLuint diff_flow_tex, GLuint flow_tex, GLuint beta_0_tex, GLuint diffusivity_tex, GLuint equation_red_tex, GLuint equation_black_tex, int level_width, int level_height, bool zero_diff_flow);
-
-private:
-       PersistentFBOSet<2> fbos;
-
-       GLuint equations_vs_obj;
-       GLuint equations_fs_obj;
-       GLuint equations_program;
-
-       GLuint uniform_I_x_y_tex, uniform_I_t_tex;
-       GLuint uniform_diff_flow_tex, uniform_base_flow_tex;
-       GLuint uniform_beta_0_tex;
-       GLuint uniform_diffusivity_tex;
-       GLuint uniform_gamma, uniform_delta, uniform_zero_diff_flow;
-};
-
 SetupEquations::SetupEquations()
 {
        equations_vs_obj = compile_shader(read_file("equations.vert"), GL_VERTEX_SHADER);
@@ -729,7 +478,7 @@ SetupEquations::SetupEquations()
        uniform_zero_diff_flow = glGetUniformLocation(equations_program, "zero_diff_flow");
 }
 
-void SetupEquations::exec(GLuint I_x_y_tex, GLuint I_t_tex, GLuint diff_flow_tex, GLuint base_flow_tex, GLuint beta_0_tex, GLuint diffusivity_tex, GLuint equation_red_tex, GLuint equation_black_tex, int level_width, int level_height, bool zero_diff_flow)
+void SetupEquations::exec(GLuint I_x_y_tex, GLuint I_t_tex, GLuint diff_flow_tex, GLuint base_flow_tex, GLuint beta_0_tex, GLuint diffusivity_tex, GLuint equation_red_tex, GLuint equation_black_tex, int level_width, int level_height, bool zero_diff_flow, int num_layers)
 {
        glUseProgram(equations_program);
 
@@ -745,32 +494,10 @@ void SetupEquations::exec(GLuint I_x_y_tex, GLuint I_t_tex, GLuint diff_flow_tex
 
        glViewport(0, 0, (level_width + 1) / 2, level_height);
        glDisable(GL_BLEND);
-       fbos.render_to({equation_red_tex, equation_black_tex});
-       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+       fbos.render_to(equation_red_tex, equation_black_tex);
+       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, num_layers);
 }
 
-// Actually solve the equation sets made by SetupEquations, by means of
-// successive over-relaxation (SOR).
-//
-// See variational_refinement.txt for more information.
-class SOR {
-public:
-       SOR();
-       void exec(GLuint diff_flow_tex, GLuint equation_red_tex, GLuint equation_black_tex, GLuint diffusivity_tex, int level_width, int level_height, int num_iterations, bool zero_diff_flow, ScopedTimer *sor_timer);
-
-private:
-       PersistentFBOSet<1> fbos;
-
-       GLuint sor_vs_obj;
-       GLuint sor_fs_obj;
-       GLuint sor_program;
-
-       GLuint uniform_diff_flow_tex;
-       GLuint uniform_equation_red_tex, uniform_equation_black_tex;
-       GLuint uniform_diffusivity_tex;
-       GLuint uniform_phase, uniform_num_nonzero_phases;
-};
-
 SOR::SOR()
 {
        sor_vs_obj = compile_shader(read_file("sor.vert"), GL_VERTEX_SHADER);
@@ -785,7 +512,7 @@ SOR::SOR()
        uniform_num_nonzero_phases = glGetUniformLocation(sor_program, "num_nonzero_phases");
 }
 
-void SOR::exec(GLuint diff_flow_tex, GLuint equation_red_tex, GLuint equation_black_tex, GLuint diffusivity_tex, int level_width, int level_height, int num_iterations, bool zero_diff_flow, ScopedTimer *sor_timer)
+void SOR::exec(GLuint diff_flow_tex, GLuint equation_red_tex, GLuint equation_black_tex, GLuint diffusivity_tex, int level_width, int level_height, int num_iterations, bool zero_diff_flow, int num_layers, ScopedTimer *sor_timer)
 {
        glUseProgram(sor_program);
 
@@ -813,7 +540,7 @@ void SOR::exec(GLuint diff_flow_tex, GLuint equation_red_tex, GLuint equation_bl
                                glProgramUniform1i(sor_program, uniform_num_nonzero_phases, 0);
                        }
                        glProgramUniform1i(sor_program, uniform_phase, 0);
-                       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+                       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, num_layers);
                        glTextureBarrier();
                }
                {
@@ -822,7 +549,7 @@ void SOR::exec(GLuint diff_flow_tex, GLuint equation_red_tex, GLuint equation_bl
                                glProgramUniform1i(sor_program, uniform_num_nonzero_phases, 1);
                        }
                        glProgramUniform1i(sor_program, uniform_phase, 1);
-                       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+                       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, num_layers);
                        if (zero_diff_flow && i == 0) {
                                glProgramUniform1i(sor_program, uniform_num_nonzero_phases, 2);
                        }
@@ -833,23 +560,6 @@ void SOR::exec(GLuint diff_flow_tex, GLuint equation_red_tex, GLuint equation_bl
        }
 }
 
-// Simply add the differential flow found by the variational refinement to the base flow.
-// The output is in base_flow_tex; we don't need to make a new texture.
-class AddBaseFlow {
-public:
-       AddBaseFlow();
-       void exec(GLuint base_flow_tex, GLuint diff_flow_tex, int level_width, int level_height);
-
-private:
-       PersistentFBOSet<1> fbos;
-
-       GLuint add_flow_vs_obj;
-       GLuint add_flow_fs_obj;
-       GLuint add_flow_program;
-
-       GLuint uniform_diff_flow_tex;
-};
-
 AddBaseFlow::AddBaseFlow()
 {
        add_flow_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
@@ -859,7 +569,7 @@ AddBaseFlow::AddBaseFlow()
        uniform_diff_flow_tex = glGetUniformLocation(add_flow_program, "diff_flow_tex");
 }
 
-void AddBaseFlow::exec(GLuint base_flow_tex, GLuint diff_flow_tex, int level_width, int level_height)
+void AddBaseFlow::exec(GLuint base_flow_tex, GLuint diff_flow_tex, int level_width, int level_height, int num_layers)
 {
        glUseProgram(add_flow_program);
 
@@ -870,26 +580,9 @@ void AddBaseFlow::exec(GLuint base_flow_tex, GLuint diff_flow_tex, int level_wid
        glBlendFunc(GL_ONE, GL_ONE);
        fbos.render_to(base_flow_tex);
 
-       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, num_layers);
 }
 
-// Take a copy of the flow, bilinearly interpolated and scaled up.
-class ResizeFlow {
-public:
-       ResizeFlow();
-       void exec(GLuint in_tex, GLuint out_tex, int input_width, int input_height, int output_width, int output_height);
-
-private:
-       PersistentFBOSet<1> fbos;
-
-       GLuint resize_flow_vs_obj;
-       GLuint resize_flow_fs_obj;
-       GLuint resize_flow_program;
-
-       GLuint uniform_flow_tex;
-       GLuint uniform_scale_factor;
-};
-
 ResizeFlow::ResizeFlow()
 {
        resize_flow_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
@@ -900,7 +593,7 @@ ResizeFlow::ResizeFlow()
        uniform_scale_factor = glGetUniformLocation(resize_flow_program, "scale_factor");
 }
 
-void ResizeFlow::exec(GLuint flow_tex, GLuint out_tex, int input_width, int input_height, int output_width, int output_height)
+void ResizeFlow::exec(GLuint flow_tex, GLuint out_tex, int input_width, int input_height, int output_width, int output_height, int num_layers)
 {
        glUseProgram(resize_flow_program);
 
@@ -912,65 +605,11 @@ void ResizeFlow::exec(GLuint flow_tex, GLuint out_tex, int input_width, int inpu
        glDisable(GL_BLEND);
        fbos.render_to(out_tex);
 
-       glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, num_layers);
 }
 
-class TexturePool {
-public:
-       GLuint get_texture(GLenum format, GLuint width, GLuint height);
-       void release_texture(GLuint tex_num);
-       GLuint get_renderbuffer(GLenum format, GLuint width, GLuint height);
-       void release_renderbuffer(GLuint tex_num);
-
-private:
-       struct Texture {
-               GLuint tex_num;
-               GLenum format;
-               GLuint width, height;
-               bool in_use = false;
-               bool is_renderbuffer = false;
-       };
-       vector<Texture> textures;
-};
-
-class DISComputeFlow {
-public:
-       DISComputeFlow(int width, int height);
-
-       enum ResizeStrategy {
-               DO_NOT_RESIZE_FLOW,
-               RESIZE_FLOW_TO_FULL_SIZE
-       };
-
-       // Returns a texture that must be released with release_texture()
-       // after use.
-       GLuint exec(GLuint tex0, GLuint tex1, ResizeStrategy resize_strategy);
-
-       void release_texture(GLuint tex) {
-               pool.release_texture(tex);
-       }
-
-private:
-       int width, height;
-       GLuint initial_flow_tex;
-       GLuint vertex_vbo, vao;
-       TexturePool pool;
-
-       // The various passes.
-       Sobel sobel;
-       MotionSearch motion_search;
-       Densify densify;
-       Prewarp prewarp;
-       Derivatives derivatives;
-       ComputeDiffusivity compute_diffusivity;
-       SetupEquations setup_equations;
-       SOR sor;
-       AddBaseFlow add_base_flow;
-       ResizeFlow resize_flow;
-};
-
-DISComputeFlow::DISComputeFlow(int width, int height)
-       : width(width), height(height)
+DISComputeFlow::DISComputeFlow(int width, int height, const OperatingPoint &op)
+       : width(width), height(height), op(op), densify(op)
 {
        // Make some samplers.
        glCreateSamplers(1, &nearest_sampler);
@@ -998,8 +637,8 @@ DISComputeFlow::DISComputeFlow(int width, int height)
        glSamplerParameterfv(zero_border_sampler, GL_TEXTURE_BORDER_COLOR, zero);
 
        // Initial flow is zero, 1x1.
-       glCreateTextures(GL_TEXTURE_2D, 1, &initial_flow_tex);
-       glTextureStorage2D(initial_flow_tex, 1, GL_RG16F, 1, 1);
+       glCreateTextures(GL_TEXTURE_2D_ARRAY, 1, &initial_flow_tex);
+       glTextureStorage3D(initial_flow_tex, 1, GL_RG16F, 1, 1, 1);
        glClearTexImage(initial_flow_tex, 0, GL_RG, GL_FLOAT, nullptr);
 
        // Set up the vertex data that will be shared between all passes.
@@ -1021,8 +660,9 @@ DISComputeFlow::DISComputeFlow(int width, int height)
        glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 }
 
-GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1, ResizeStrategy resize_strategy)
+GLuint DISComputeFlow::exec(GLuint tex, FlowDirection flow_direction, ResizeStrategy resize_strategy)
 {
+       int num_layers = (flow_direction == FORWARD_AND_BACKWARD) ? 2 : 1;
        int prev_level_width = 1, prev_level_height = 1;
        GLuint prev_level_flow_tex = initial_flow_tex;
 
@@ -1031,14 +671,14 @@ GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1, ResizeStrategy resize_stra
        glBindVertexArray(vao);
 
        ScopedTimer total_timer("Compute flow", &timers);
-       for (int level = coarsest_level; level >= int(finest_level); --level) {
+       for (int level = op.coarsest_level; level >= int(op.finest_level); --level) {
                char timer_name[256];
                snprintf(timer_name, sizeof(timer_name), "Level %d (%d x %d)", level, width >> level, height >> level);
                ScopedTimer level_timer(timer_name, &total_timer);
 
                int level_width = width >> level;
                int level_height = height >> level;
-               float patch_spacing_pixels = patch_size_pixels * (1.0f - patch_overlap_ratio);
+               float patch_spacing_pixels = op.patch_size_pixels * (1.0f - op.patch_overlap_ratio);
 
                // Make sure we have patches at least every Nth pixel, e.g. for width=9
                // and patch_spacing=3 (the default), we put out patch centers in
@@ -1050,44 +690,41 @@ GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1, ResizeStrategy resize_stra
                // Make sure we always read from the correct level; the chosen
                // mipmapping could otherwise be rather unpredictable, especially
                // during motion search.
-               GLuint tex0_view, tex1_view;
-               glGenTextures(1, &tex0_view);
-               glTextureView(tex0_view, GL_TEXTURE_2D, tex0, GL_R8, level, 1, 0, 1);
-               glGenTextures(1, &tex1_view);
-               glTextureView(tex1_view, GL_TEXTURE_2D, tex1, GL_R8, level, 1, 0, 1);
+               GLuint tex_view;
+               glGenTextures(1, &tex_view);
+               glTextureView(tex_view, GL_TEXTURE_2D_ARRAY, tex, GL_R8, level, 1, 0, 2);
 
-               // Create a new texture; we could be fancy and render use a multi-level
-               // texture, but meh.
-               GLuint grad0_tex = pool.get_texture(GL_R32UI, level_width, level_height);
+               // Create a new texture to hold the gradients.
+               GLuint grad_tex = pool.get_texture(GL_R32UI, level_width, level_height, num_layers);
 
                // Find the derivative.
                {
                        ScopedTimer timer("Sobel", &level_timer);
-                       sobel.exec(tex0_view, grad0_tex, level_width, level_height);
+                       sobel.exec(tex_view, grad_tex, level_width, level_height, num_layers);
                }
 
                // Motion search to find the initial flow. We use the flow from the previous
                // level (sampled bilinearly; no fancy tricks) as a guide, then search from there.
 
                // Create an output flow texture.
-               GLuint flow_out_tex = pool.get_texture(GL_RGB16F, width_patches, height_patches);
+               GLuint flow_out_tex = pool.get_texture(GL_RGB16F, width_patches, height_patches, num_layers);
 
                // And draw.
                {
                        ScopedTimer timer("Motion search", &level_timer);
-                       motion_search.exec(tex0_view, tex1_view, grad0_tex, prev_level_flow_tex, flow_out_tex, level_width, level_height, prev_level_width, prev_level_height, width_patches, height_patches);
+                       motion_search.exec(tex_view, grad_tex, prev_level_flow_tex, flow_out_tex, level_width, level_height, prev_level_width, prev_level_height, width_patches, height_patches, num_layers);
                }
-               pool.release_texture(grad0_tex);
+               pool.release_texture(grad_tex);
 
                // Densification.
 
                // Set up an output texture (cleared in Densify).
-               GLuint dense_flow_tex = pool.get_texture(GL_RGB16F, level_width, level_height);
+               GLuint dense_flow_tex = pool.get_texture(GL_RGB16F, level_width, level_height, num_layers);
 
                // And draw.
                {
                        ScopedTimer timer("Densification", &level_timer);
-                       densify.exec(tex0_view, tex1_view, flow_out_tex, dense_flow_tex, level_width, level_height, width_patches, height_patches);
+                       densify.exec(tex_view, flow_out_tex, dense_flow_tex, level_width, level_height, width_patches, height_patches, num_layers);
                }
                pool.release_texture(flow_out_tex);
 
@@ -1101,60 +738,59 @@ GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1, ResizeStrategy resize_stra
                // in pixels, not 0..1 normalized OpenGL texture coordinates.
                // This is because variational refinement depends so heavily on derivatives,
                // which are measured in intensity levels per pixel.
-               GLuint I_tex = pool.get_texture(GL_R16F, level_width, level_height);
-               GLuint I_t_tex = pool.get_texture(GL_R16F, level_width, level_height);
-               GLuint base_flow_tex = pool.get_texture(GL_RG16F, level_width, level_height);
+               GLuint I_tex = pool.get_texture(GL_R16F, level_width, level_height, num_layers);
+               GLuint I_t_tex = pool.get_texture(GL_R16F, level_width, level_height, num_layers);
+               GLuint base_flow_tex = pool.get_texture(GL_RG16F, level_width, level_height, num_layers);
                {
                        ScopedTimer timer("Prewarping", &varref_timer);
-                       prewarp.exec(tex0_view, tex1_view, dense_flow_tex, I_tex, I_t_tex, base_flow_tex, level_width, level_height);
+                       prewarp.exec(tex_view, dense_flow_tex, I_tex, I_t_tex, base_flow_tex, level_width, level_height, num_layers);
                }
                pool.release_texture(dense_flow_tex);
-               glDeleteTextures(1, &tex0_view);
-               glDeleteTextures(1, &tex1_view);
+               glDeleteTextures(1, &tex_view);
 
                // Calculate I_x and I_y. We're only calculating first derivatives;
                // the others will be taken on-the-fly in order to sample from fewer
                // textures overall, since sampling from the L1 cache is cheap.
                // (TODO: Verify that this is indeed faster than making separate
                // double-derivative textures.)
-               GLuint I_x_y_tex = pool.get_texture(GL_RG16F, level_width, level_height);
-               GLuint beta_0_tex = pool.get_texture(GL_R16F, level_width, level_height);
+               GLuint I_x_y_tex = pool.get_texture(GL_RG16F, level_width, level_height, num_layers);
+               GLuint beta_0_tex = pool.get_texture(GL_R16F, level_width, level_height, num_layers);
                {
                        ScopedTimer timer("First derivatives", &varref_timer);
-                       derivatives.exec(I_tex, I_x_y_tex, beta_0_tex, level_width, level_height);
+                       derivatives.exec(I_tex, I_x_y_tex, beta_0_tex, level_width, level_height, num_layers);
                }
                pool.release_texture(I_tex);
 
                // We need somewhere to store du and dv (the flow increment, relative
                // to the non-refined base flow u0 and v0). It's initially garbage,
                // but not read until we've written something sane to it.
-               GLuint diff_flow_tex = pool.get_texture(GL_RG16F, level_width, level_height);
+               GLuint diff_flow_tex = pool.get_texture(GL_RG16F, level_width, level_height, num_layers);
 
                // And for diffusivity.
-               GLuint diffusivity_tex = pool.get_texture(GL_R16F, level_width, level_height);
+               GLuint diffusivity_tex = pool.get_texture(GL_R16F, level_width, level_height, num_layers);
 
                // And finally for the equation set. See SetupEquations for
                // the storage format.
-               GLuint equation_red_tex = pool.get_texture(GL_RGBA32UI, (level_width + 1) / 2, level_height);
-               GLuint equation_black_tex = pool.get_texture(GL_RGBA32UI, (level_width + 1) / 2, level_height);
+               GLuint equation_red_tex = pool.get_texture(GL_RGBA32UI, (level_width + 1) / 2, level_height, num_layers);
+               GLuint equation_black_tex = pool.get_texture(GL_RGBA32UI, (level_width + 1) / 2, level_height, num_layers);
 
                for (int outer_idx = 0; outer_idx < level + 1; ++outer_idx) {
                        // Calculate the diffusivity term for each pixel.
                        {
                                ScopedTimer timer("Compute diffusivity", &varref_timer);
-                               compute_diffusivity.exec(base_flow_tex, diff_flow_tex, diffusivity_tex, level_width, level_height, outer_idx == 0);
+                               compute_diffusivity.exec(base_flow_tex, diff_flow_tex, diffusivity_tex, level_width, level_height, outer_idx == 0, num_layers);
                        }
 
                        // Set up the 2x2 equation system for each pixel.
                        {
                                ScopedTimer timer("Set up equations", &varref_timer);
-                               setup_equations.exec(I_x_y_tex, I_t_tex, diff_flow_tex, base_flow_tex, beta_0_tex, diffusivity_tex, equation_red_tex, equation_black_tex, level_width, level_height, outer_idx == 0);
+                               setup_equations.exec(I_x_y_tex, I_t_tex, diff_flow_tex, base_flow_tex, beta_0_tex, diffusivity_tex, equation_red_tex, equation_black_tex, level_width, level_height, outer_idx == 0, num_layers);
                        }
 
                        // Run a few SOR iterations. Note that these are to/from the same texture.
                        {
                                ScopedTimer timer("SOR", &varref_timer);
-                               sor.exec(diff_flow_tex, equation_red_tex, equation_black_tex, diffusivity_tex, level_width, level_height, 5, outer_idx == 0, &timer);
+                               sor.exec(diff_flow_tex, equation_red_tex, equation_black_tex, diffusivity_tex, level_width, level_height, 5, outer_idx == 0, num_layers, &timer);
                        }
                }
 
@@ -1171,9 +807,9 @@ GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1, ResizeStrategy resize_stra
                //
                // Disabling this doesn't save any time (although we could easily make it so that
                // it is more efficient), but it helps debug the motion search.
-               if (enable_variational_refinement) {
+               if (op.variational_refinement) {
                        ScopedTimer timer("Add differential flow", &varref_timer);
-                       add_base_flow.exec(base_flow_tex, diff_flow_tex, level_width, level_height);
+                       add_base_flow.exec(base_flow_tex, diff_flow_tex, level_width, level_height, num_layers);
                }
                pool.release_texture(diff_flow_tex);
 
@@ -1191,65 +827,38 @@ GLuint DISComputeFlow::exec(GLuint tex0, GLuint tex1, ResizeStrategy resize_stra
        }
 
        // Scale up the flow to the final size (if needed).
-       if (finest_level == 0 || resize_strategy == DO_NOT_RESIZE_FLOW) {
+       if (op.finest_level == 0 || resize_strategy == DO_NOT_RESIZE_FLOW) {
                return prev_level_flow_tex;
        } else {
-               GLuint final_tex = pool.get_texture(GL_RG16F, width, height);
-               resize_flow.exec(prev_level_flow_tex, final_tex, prev_level_width, prev_level_height, width, height);
+               GLuint final_tex = pool.get_texture(GL_RG16F, width, height, num_layers);
+               resize_flow.exec(prev_level_flow_tex, final_tex, prev_level_width, prev_level_height, width, height, num_layers);
                pool.release_texture(prev_level_flow_tex);
                return final_tex;
        }
 }
 
-// Forward-warp the flow half-way (or rather, by alpha). A non-zero “splatting”
-// radius fills most of the holes.
-class Splat {
-public:
-       Splat();
-
-       // alpha is the time of the interpolated frame (0..1).
-       void exec(GLuint tex0, GLuint tex1, GLuint forward_flow_tex, GLuint backward_flow_tex, GLuint flow_tex, GLuint depth_rb, int width, int height, float alpha);
-
-private:
-       PersistentFBOSetWithDepth<1> fbos;
-
-       GLuint splat_vs_obj;
-       GLuint splat_fs_obj;
-       GLuint splat_program;
-
-       GLuint uniform_invert_flow, uniform_splat_size, uniform_alpha;
-       GLuint uniform_image0_tex, uniform_image1_tex, uniform_flow_tex;
-       GLuint uniform_inv_flow_size;
-};
-
-Splat::Splat()
+Splat::Splat(const OperatingPoint &op)
+       : op(op)
 {
        splat_vs_obj = compile_shader(read_file("splat.vert"), GL_VERTEX_SHADER);
        splat_fs_obj = compile_shader(read_file("splat.frag"), GL_FRAGMENT_SHADER);
        splat_program = link_program(splat_vs_obj, splat_fs_obj);
 
-       uniform_invert_flow = glGetUniformLocation(splat_program, "invert_flow");
        uniform_splat_size = glGetUniformLocation(splat_program, "splat_size");
        uniform_alpha = glGetUniformLocation(splat_program, "alpha");
-       uniform_image0_tex = glGetUniformLocation(splat_program, "image0_tex");
-       uniform_image1_tex = glGetUniformLocation(splat_program, "image1_tex");
+       uniform_image_tex = glGetUniformLocation(splat_program, "image_tex");
        uniform_flow_tex = glGetUniformLocation(splat_program, "flow_tex");
        uniform_inv_flow_size = glGetUniformLocation(splat_program, "inv_flow_size");
 }
 
-void Splat::exec(GLuint tex0, GLuint tex1, GLuint forward_flow_tex, GLuint backward_flow_tex, GLuint flow_tex, GLuint depth_rb, int width, int height, float alpha)
+void Splat::exec(GLuint image_tex, GLuint bidirectional_flow_tex, GLuint flow_tex, GLuint depth_rb, int width, int height, float alpha)
 {
        glUseProgram(splat_program);
 
-       bind_sampler(splat_program, uniform_image0_tex, 0, tex0, linear_sampler);
-       bind_sampler(splat_program, uniform_image1_tex, 1, tex1, linear_sampler);
+       bind_sampler(splat_program, uniform_image_tex, 0, image_tex, linear_sampler);
+       bind_sampler(splat_program, uniform_flow_tex, 1, bidirectional_flow_tex, nearest_sampler);
 
-       // FIXME: This is set to 1.0 right now so not to trigger Haswell's “PMA stall”.
-       // Move to 2.0 later, or even 4.0.
-       // (Since we have hole filling, it's not critical, but larger values seem to do
-       // better than hole filling for large motion, blurs etc.)
-       float splat_size = 1.0f;  // 4x4 splat means 16x overdraw, 2x2 splat means 4x overdraw.
-       glProgramUniform2f(splat_program, uniform_splat_size, splat_size / width, splat_size / height);
+       glProgramUniform2f(splat_program, uniform_splat_size, op.splat_size / width, op.splat_size / height);
        glProgramUniform1f(splat_program, uniform_alpha, alpha);
        glProgramUniform2f(splat_program, uniform_inv_flow_size, 1.0f / width, 1.0f / height);
 
@@ -1266,52 +875,11 @@ void Splat::exec(GLuint tex0, GLuint tex1, GLuint forward_flow_tex, GLuint backw
        glClearDepth(1.0f);  // Effectively infinity.
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
-       // Do forward splatting.
-       bind_sampler(splat_program, uniform_flow_tex, 2, forward_flow_tex, nearest_sampler);
-       glProgramUniform1i(splat_program, uniform_invert_flow, 0);
-       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width * height);
-
-       // Do backward splatting.
-       bind_sampler(splat_program, uniform_flow_tex, 2, backward_flow_tex, nearest_sampler);
-       glProgramUniform1i(splat_program, uniform_invert_flow, 1);
-       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width * height);
+       glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width * height * 2);
 
        glDisable(GL_DEPTH_TEST);
 }
 
-// Doing good and fast hole-filling on a GPU is nontrivial. We choose an option
-// that's fairly simple (given that most holes are really small) and also hopefully
-// cheap should the holes not be so small. Conceptually, we look for the first
-// non-hole to the left of us (ie., shoot a ray until we hit something), then
-// the first non-hole to the right of us, then up and down, and then average them
-// all together. It's going to create “stars” if the holes are big, but OK, that's
-// a tradeoff.
-//
-// Our implementation here is efficient assuming that the hierarchical Z-buffer is
-// on even for shaders that do discard (this typically kills early Z, but hopefully
-// not hierarchical Z); we set up Z so that only holes are written to, which means
-// that as soon as a hole is filled, the rasterizer should just skip it. Most of the
-// fullscreen quads should just be discarded outright, really.
-class HoleFill {
-public:
-       HoleFill();
-
-       // Output will be in flow_tex, temp_tex[0, 1, 2], representing the filling
-       // from the down, left, right and up, respectively. Use HoleBlend to merge
-       // them into one.
-       void exec(GLuint flow_tex, GLuint depth_rb, GLuint temp_tex[3], int width, int height);
-
-private:
-       PersistentFBOSetWithDepth<1> fbos;
-
-       GLuint fill_vs_obj;
-       GLuint fill_fs_obj;
-       GLuint fill_program;
-
-       GLuint uniform_tex;
-       GLuint uniform_z, uniform_sample_offset;
-};
-
 HoleFill::HoleFill()
 {
        fill_vs_obj = compile_shader(read_file("hole_fill.vert"), GL_VERTEX_SHADER);
@@ -1376,25 +944,6 @@ void HoleFill::exec(GLuint flow_tex, GLuint depth_rb, GLuint temp_tex[3], int wi
        glDisable(GL_DEPTH_TEST);
 }
 
-// Blend the four directions from HoleFill into one pixel, so that single-pixel
-// holes become the average of their four neighbors.
-class HoleBlend {
-public:
-       HoleBlend();
-
-       void exec(GLuint flow_tex, GLuint depth_rb, GLuint temp_tex[3], int width, int height);
-
-private:
-       PersistentFBOSetWithDepth<1> fbos;
-
-       GLuint blend_vs_obj;
-       GLuint blend_fs_obj;
-       GLuint blend_program;
-
-       GLuint uniform_left_tex, uniform_right_tex, uniform_up_tex, uniform_down_tex;
-       GLuint uniform_z, uniform_sample_offset;
-};
-
 HoleBlend::HoleBlend()
 {
        blend_vs_obj = compile_shader(read_file("hole_fill.vert"), GL_VERTEX_SHADER);  // Reuse the vertex shader from the fill.
@@ -1433,40 +982,23 @@ void HoleBlend::exec(GLuint flow_tex, GLuint depth_rb, GLuint temp_tex[3], int w
        glDisable(GL_DEPTH_TEST);
 }
 
-class Blend {
-public:
-       Blend();
-       void exec(GLuint tex0, GLuint tex1, GLuint flow_tex, GLuint output_tex, int width, int height, float alpha);
-
-private:
-       PersistentFBOSet<1> fbos;
-       GLuint blend_vs_obj;
-       GLuint blend_fs_obj;
-       GLuint blend_program;
-
-       GLuint uniform_image0_tex, uniform_image1_tex, uniform_flow_tex;
-       GLuint uniform_alpha, uniform_flow_consistency_tolerance;
-};
-
 Blend::Blend()
 {
        blend_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
        blend_fs_obj = compile_shader(read_file("blend.frag"), GL_FRAGMENT_SHADER);
        blend_program = link_program(blend_vs_obj, blend_fs_obj);
 
-       uniform_image0_tex = glGetUniformLocation(blend_program, "image0_tex");
-       uniform_image1_tex = glGetUniformLocation(blend_program, "image1_tex");
+       uniform_image_tex = glGetUniformLocation(blend_program, "image_tex");
        uniform_flow_tex = glGetUniformLocation(blend_program, "flow_tex");
        uniform_alpha = glGetUniformLocation(blend_program, "alpha");
        uniform_flow_consistency_tolerance = glGetUniformLocation(blend_program, "flow_consistency_tolerance");
 }
 
-void Blend::exec(GLuint tex0, GLuint tex1, GLuint flow_tex, GLuint output_tex, int level_width, int level_height, float alpha)
+void Blend::exec(GLuint image_tex, GLuint flow_tex, GLuint output_tex, int level_width, int level_height, float alpha)
 {
        glUseProgram(blend_program);
-       bind_sampler(blend_program, uniform_image0_tex, 0, tex0, linear_sampler);
-       bind_sampler(blend_program, uniform_image1_tex, 1, tex1, linear_sampler);
-       bind_sampler(blend_program, uniform_flow_tex, 2, flow_tex, linear_sampler);  // May be upsampled.
+       bind_sampler(blend_program, uniform_image_tex, 0, image_tex, linear_sampler);
+       bind_sampler(blend_program, uniform_flow_tex, 1, flow_tex, linear_sampler);  // May be upsampled.
        glProgramUniform1f(blend_program, uniform_alpha, alpha);
 
        glViewport(0, 0, level_width, level_height);
@@ -1475,32 +1007,8 @@ void Blend::exec(GLuint tex0, GLuint tex1, GLuint flow_tex, GLuint output_tex, i
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
-class Interpolate {
-public:
-       Interpolate(int width, int height, int flow_level);
-
-       // Returns a texture that must be released with release_texture()
-       // after use. tex0 and tex1 must be RGBA8 textures with mipmaps
-       // (unless flow_level == 0).
-       GLuint exec(GLuint tex0, GLuint tex1, GLuint forward_flow_tex, GLuint backward_flow_tex, GLuint width, GLuint height, float alpha);
-
-       void release_texture(GLuint tex) {
-               pool.release_texture(tex);
-       }
-
-private:
-       int width, height, flow_level;
-       GLuint vertex_vbo, vao;
-       TexturePool pool;
-
-       Splat splat;
-       HoleFill hole_fill;
-       HoleBlend hole_blend;
-       Blend blend;
-};
-
-Interpolate::Interpolate(int width, int height, int flow_level)
-       : width(width), height(height), flow_level(flow_level) {
+Interpolate::Interpolate(int width, int height, const OperatingPoint &op)
+       : width(width), height(height), flow_level(op.finest_level), op(op), splat(op) {
        // Set up the vertex data that will be shared between all passes.
        float vertices[] = {
                0.0f, 1.0f,
@@ -1520,7 +1028,7 @@ Interpolate::Interpolate(int width, int height, int flow_level)
        glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 }
 
-GLuint Interpolate::exec(GLuint tex0, GLuint tex1, GLuint forward_flow_tex, GLuint backward_flow_tex, GLuint width, GLuint height, float alpha)
+GLuint Interpolate::exec(GLuint image_tex, GLuint bidirectional_flow_tex, GLuint width, GLuint height, float alpha)
 {
        GPUTimers timers;
 
@@ -1529,24 +1037,21 @@ GLuint Interpolate::exec(GLuint tex0, GLuint tex1, GLuint forward_flow_tex, GLui
        glBindVertexArray(vao);
 
        // Pick out the right level to test splatting results on.
-       GLuint tex0_view, tex1_view;
-       glGenTextures(1, &tex0_view);
-       glTextureView(tex0_view, GL_TEXTURE_2D, tex0, GL_RGBA8, flow_level, 1, 0, 1);
-       glGenTextures(1, &tex1_view);
-       glTextureView(tex1_view, GL_TEXTURE_2D, tex1, GL_RGBA8, flow_level, 1, 0, 1);
+       GLuint tex_view;
+       glGenTextures(1, &tex_view);
+       glTextureView(tex_view, GL_TEXTURE_2D_ARRAY, image_tex, GL_RGBA8, flow_level, 1, 0, 2);
 
        int flow_width = width >> flow_level;
        int flow_height = height >> flow_level;
 
        GLuint flow_tex = pool.get_texture(GL_RG16F, flow_width, flow_height);
-       GLuint depth_rb = pool.get_renderbuffer(GL_DEPTH_COMPONENT32F, flow_width, flow_height);  // Used for ranking flows.
+       GLuint depth_rb = pool.get_renderbuffer(GL_DEPTH_COMPONENT16, flow_width, flow_height);  // Used for ranking flows.
 
        {
                ScopedTimer timer("Splat", &total_timer);
-               splat.exec(tex0_view, tex1_view, forward_flow_tex, backward_flow_tex, flow_tex, depth_rb, flow_width, flow_height, alpha);
+               splat.exec(tex_view, bidirectional_flow_tex, flow_tex, depth_rb, flow_width, flow_height, alpha);
        }
-       glDeleteTextures(1, &tex0_view);
-       glDeleteTextures(1, &tex1_view);
+       glDeleteTextures(1, &tex_view);
 
        GLuint temp_tex[3];
        temp_tex[0] = pool.get_texture(GL_RG16F, flow_width, flow_height);
@@ -1567,7 +1072,7 @@ GLuint Interpolate::exec(GLuint tex0, GLuint tex1, GLuint forward_flow_tex, GLui
        GLuint output_tex = pool.get_texture(GL_RGBA8, width, height);
        {
                ScopedTimer timer("Blend", &total_timer);
-               blend.exec(tex0, tex1, flow_tex, output_tex, width, height, alpha);
+               blend.exec(image_tex, flow_tex, output_tex, width, height, alpha);
        }
        pool.release_texture(flow_tex);
        total_timer.end();
@@ -1578,22 +1083,28 @@ GLuint Interpolate::exec(GLuint tex0, GLuint tex1, GLuint forward_flow_tex, GLui
        return output_tex;
 }
 
-GLuint TexturePool::get_texture(GLenum format, GLuint width, GLuint height)
+GLuint TexturePool::get_texture(GLenum format, GLuint width, GLuint height, GLuint num_layers)
 {
        for (Texture &tex : textures) {
                if (!tex.in_use && !tex.is_renderbuffer && tex.format == format &&
-                   tex.width == width && tex.height == height) {
+                   tex.width == width && tex.height == height && tex.num_layers == num_layers) {
                        tex.in_use = true;
                        return tex.tex_num;
                }
        }
 
        Texture tex;
-       glCreateTextures(GL_TEXTURE_2D, 1, &tex.tex_num);
-       glTextureStorage2D(tex.tex_num, 1, format, width, height);
+       if (num_layers == 0) {
+               glCreateTextures(GL_TEXTURE_2D, 1, &tex.tex_num);
+               glTextureStorage2D(tex.tex_num, 1, format, width, height);
+       } else {
+               glCreateTextures(GL_TEXTURE_2D_ARRAY, 1, &tex.tex_num);
+               glTextureStorage3D(tex.tex_num, 1, format, width, height, num_layers);
+       }
        tex.format = format;
        tex.width = width;
        tex.height = height;
+       tex.num_layers = num_layers;
        tex.in_use = true;
        tex.is_renderbuffer = false;
        textures.push_back(tex);
@@ -1644,7 +1155,7 @@ void TexturePool::release_renderbuffer(GLuint tex_num)
                        return;
                }
        }
-       assert(false);
+       //assert(false);
 }
 
 // OpenGL uses a bottom-left coordinate system, .flo files use a top-left coordinate system.
@@ -1789,42 +1300,51 @@ void compute_flow_only(int argc, char **argv, int optind)
                exit(1);
        }
 
+       // Move them into an array texture, since that's how the rest of the code
+       // would like them.
+       GLuint image_tex;
+       glCreateTextures(GL_TEXTURE_2D_ARRAY, 1, &image_tex);
+       glTextureStorage3D(image_tex, 1, GL_RGBA8, width1, height1, 2);
+       glCopyImageSubData(tex0, GL_TEXTURE_2D, 0, 0, 0, 0, image_tex, GL_TEXTURE_2D_ARRAY, 0, 0, 0, 0, width1, height1, 1);
+       glCopyImageSubData(tex1, GL_TEXTURE_2D, 0, 0, 0, 0, image_tex, GL_TEXTURE_2D_ARRAY, 0, 0, 0, 1, width1, height1, 1);
+       glDeleteTextures(1, &tex0);
+       glDeleteTextures(1, &tex1);
+
        // Set up some PBOs to do asynchronous readback.
        GLuint pbos[5];
        glCreateBuffers(5, pbos);
        for (int i = 0; i < 5; ++i) {
-               glNamedBufferData(pbos[i], width1 * height1 * 2 * sizeof(float), nullptr, GL_STREAM_READ);
+               glNamedBufferData(pbos[i], width1 * height1 * 2 * 2 * sizeof(float), nullptr, GL_STREAM_READ);
                spare_pbos.push(pbos[i]);
        }
 
        int levels = find_num_levels(width1, height1);
-       GLuint tex0_gray, tex1_gray;
-       glCreateTextures(GL_TEXTURE_2D, 1, &tex0_gray);
-       glCreateTextures(GL_TEXTURE_2D, 1, &tex1_gray);
-       glTextureStorage2D(tex0_gray, levels, GL_R8, width1, height1);
-       glTextureStorage2D(tex1_gray, levels, GL_R8, width1, height1);
 
-       GrayscaleConversion gray;
-       gray.exec(tex0, tex0_gray, width1, height1);
-       glDeleteTextures(1, &tex0);
-       glGenerateTextureMipmap(tex0_gray);
+       GLuint tex_gray;
+       glCreateTextures(GL_TEXTURE_2D_ARRAY, 1, &tex_gray);
+       glTextureStorage3D(tex_gray, levels, GL_R8, width1, height1, 2);
 
-       gray.exec(tex1, tex1_gray, width1, height1);
-       glDeleteTextures(1, &tex1);
-       glGenerateTextureMipmap(tex1_gray);
+       GrayscaleConversion gray;
+       gray.exec(image_tex, tex_gray, width1, height1, /*num_layers=*/2);
+       glGenerateTextureMipmap(tex_gray);
 
-       DISComputeFlow compute_flow(width1, height1);
+       OperatingPoint op = operating_point3;
+       if (!enable_variational_refinement) {
+               op.variational_refinement = false;
+       }
+       DISComputeFlow compute_flow(width1, height1, op);
 
        if (enable_warmup) {
                in_warmup = true;
                for (int i = 0; i < 10; ++i) {
-                       GLuint final_tex = compute_flow.exec(tex0_gray, tex1_gray, DISComputeFlow::RESIZE_FLOW_TO_FULL_SIZE);
+                       GLuint final_tex = compute_flow.exec(tex_gray, DISComputeFlow::FORWARD, DISComputeFlow::RESIZE_FLOW_TO_FULL_SIZE);
                        compute_flow.release_texture(final_tex);
                }
                in_warmup = false;
        }
 
-       GLuint final_tex = compute_flow.exec(tex0_gray, tex1_gray, DISComputeFlow::RESIZE_FLOW_TO_FULL_SIZE);
+       GLuint final_tex = compute_flow.exec(tex_gray, DISComputeFlow::FORWARD, DISComputeFlow::RESIZE_FLOW_TO_FULL_SIZE);
+       //GLuint final_tex = compute_flow.exec(tex_gray, DISComputeFlow::FORWARD_AND_BACKWARD, DISComputeFlow::RESIZE_FLOW_TO_FULL_SIZE);
 
        schedule_read<FlowType>(final_tex, width1, height1, filename0, filename1, flow_filename, "flow.ppm");
        compute_flow.release_texture(final_tex);
@@ -1843,8 +1363,7 @@ void compute_flow_only(int argc, char **argv, int optind)
                                filename0, width, height, width1, height1);
                        exit(1);
                }
-               gray.exec(tex0, tex0_gray, width, height);
-               glGenerateTextureMipmap(tex0_gray);
+               glCopyImageSubData(tex0, GL_TEXTURE_2D, 0, 0, 0, 0, image_tex, GL_TEXTURE_2D_ARRAY, 0, 0, 0, 0, width1, height1, 1);
                glDeleteTextures(1, &tex0);
 
                GLuint tex1 = load_texture(filename1, &width, &height, WITHOUT_MIPMAPS);
@@ -1853,17 +1372,18 @@ void compute_flow_only(int argc, char **argv, int optind)
                                filename1, width, height, width1, height1);
                        exit(1);
                }
-               gray.exec(tex1, tex1_gray, width, height);
-               glGenerateTextureMipmap(tex1_gray);
+               glCopyImageSubData(tex1, GL_TEXTURE_2D, 0, 0, 0, 0, image_tex, GL_TEXTURE_2D_ARRAY, 0, 0, 0, 1, width1, height1, 1);
                glDeleteTextures(1, &tex1);
 
-               GLuint final_tex = compute_flow.exec(tex0_gray, tex1_gray, DISComputeFlow::RESIZE_FLOW_TO_FULL_SIZE);
+               gray.exec(image_tex, tex_gray, width1, height1, /*num_layers=*/2);
+               glGenerateTextureMipmap(tex_gray);
+
+               GLuint final_tex = compute_flow.exec(tex_gray, DISComputeFlow::FORWARD, DISComputeFlow::RESIZE_FLOW_TO_FULL_SIZE);
 
                schedule_read<FlowType>(final_tex, width1, height1, filename0, filename1, flow_filename, "");
                compute_flow.release_texture(final_tex);
        }
-       glDeleteTextures(1, &tex0_gray);
-       glDeleteTextures(1, &tex1_gray);
+       glDeleteTextures(1, &tex_gray);
 
        while (!reads_in_progress.empty()) {
                finish_one_read<FlowType>(width1, height1);
@@ -1893,6 +1413,18 @@ void interpolate_image(int argc, char **argv, int optind)
                exit(1);
        }
 
+       // Move them into an array texture, since that's how the rest of the code
+       // would like them.
+       int levels = find_num_levels(width1, height1);
+       GLuint image_tex;
+       glCreateTextures(GL_TEXTURE_2D_ARRAY, 1, &image_tex);
+       glTextureStorage3D(image_tex, levels, GL_RGBA8, width1, height1, 2);
+       glCopyImageSubData(tex0, GL_TEXTURE_2D, 0, 0, 0, 0, image_tex, GL_TEXTURE_2D_ARRAY, 0, 0, 0, 0, width1, height1, 1);
+       glCopyImageSubData(tex1, GL_TEXTURE_2D, 0, 0, 0, 0, image_tex, GL_TEXTURE_2D_ARRAY, 0, 0, 0, 1, width1, height1, 1);
+       glDeleteTextures(1, &tex0);
+       glDeleteTextures(1, &tex1);
+       glGenerateTextureMipmap(image_tex);
+
        // Set up some PBOs to do asynchronous readback.
        GLuint pbos[5];
        glCreateBuffers(5, pbos);
@@ -1901,45 +1433,39 @@ void interpolate_image(int argc, char **argv, int optind)
                spare_pbos.push(pbos[i]);
        }
 
-       DISComputeFlow compute_flow(width1, height1);
+       OperatingPoint op = operating_point3;
+       if (!enable_variational_refinement) {
+               op.variational_refinement = false;
+       }
+       DISComputeFlow compute_flow(width1, height1, op);
        GrayscaleConversion gray;
-       Interpolate interpolate(width1, height1, finest_level);
-
-       int levels = find_num_levels(width1, height1);
-       GLuint tex0_gray, tex1_gray;
-       glCreateTextures(GL_TEXTURE_2D, 1, &tex0_gray);
-       glCreateTextures(GL_TEXTURE_2D, 1, &tex1_gray);
-       glTextureStorage2D(tex0_gray, levels, GL_R8, width1, height1);
-       glTextureStorage2D(tex1_gray, levels, GL_R8, width1, height1);
-
-       gray.exec(tex0, tex0_gray, width1, height1);
-       glGenerateTextureMipmap(tex0_gray);
+       Interpolate interpolate(width1, height1, op);
 
-       gray.exec(tex1, tex1_gray, width1, height1);
-       glGenerateTextureMipmap(tex1_gray);
+       GLuint tex_gray;
+       glCreateTextures(GL_TEXTURE_2D_ARRAY, 1, &tex_gray);
+       glTextureStorage3D(tex_gray, levels, GL_R8, width1, height1, 2);
+       gray.exec(image_tex, tex_gray, width1, height1, /*num_layers=*/2);
+       glGenerateTextureMipmap(tex_gray);
 
        if (enable_warmup) {
                in_warmup = true;
                for (int i = 0; i < 10; ++i) {
-                       GLuint forward_flow_tex = compute_flow.exec(tex0_gray, tex1_gray, DISComputeFlow::DO_NOT_RESIZE_FLOW);
-                       GLuint backward_flow_tex = compute_flow.exec(tex1_gray, tex0_gray, DISComputeFlow::DO_NOT_RESIZE_FLOW);
-                       GLuint interpolated_tex = interpolate.exec(tex0, tex1, forward_flow_tex, backward_flow_tex, width1, height1, 0.5f);
-                       compute_flow.release_texture(forward_flow_tex);
-                       compute_flow.release_texture(backward_flow_tex);
+                       GLuint bidirectional_flow_tex = compute_flow.exec(tex_gray, DISComputeFlow::FORWARD_AND_BACKWARD, DISComputeFlow::DO_NOT_RESIZE_FLOW);
+                       GLuint interpolated_tex = interpolate.exec(image_tex, bidirectional_flow_tex, width1, height1, 0.5f);
+                       compute_flow.release_texture(bidirectional_flow_tex);
                        interpolate.release_texture(interpolated_tex);
                }
                in_warmup = false;
        }
 
-       GLuint forward_flow_tex = compute_flow.exec(tex0_gray, tex1_gray, DISComputeFlow::DO_NOT_RESIZE_FLOW);
-       GLuint backward_flow_tex = compute_flow.exec(tex1_gray, tex0_gray, DISComputeFlow::DO_NOT_RESIZE_FLOW);
+       GLuint bidirectional_flow_tex = compute_flow.exec(tex_gray, DISComputeFlow::FORWARD_AND_BACKWARD, DISComputeFlow::DO_NOT_RESIZE_FLOW);
 
        for (int frameno = 1; frameno < 60; ++frameno) {
                char ppm_filename[256];
                snprintf(ppm_filename, sizeof(ppm_filename), "interp%04d.ppm", frameno);
 
                float alpha = frameno / 60.0f;
-               GLuint interpolated_tex = interpolate.exec(tex0, tex1, forward_flow_tex, backward_flow_tex, width1, height1, alpha);
+               GLuint interpolated_tex = interpolate.exec(image_tex, bidirectional_flow_tex, width1, height1, alpha);
 
                schedule_read<RGBAType>(interpolated_tex, width1, height1, filename0, filename1, "", ppm_filename);
                interpolate.release_texture(interpolated_tex);