]> git.sesse.net Git - nageru/blobdiff - flow.cpp
Refactor FBO creation. A step on the way to persistent FBOs and temporary textures.
[nageru] / flow.cpp
index 05ddfcf2bc370c9b5b3109e8a97782bb14287821..cf208a64d0efcb8f4dfe3a1278e28f450bdb0434 100644 (file)
--- a/flow.cpp
+++ b/flow.cpp
@@ -11,6 +11,7 @@
 #include <SDL2/SDL_video.h>
 
 #include <assert.h>
+#include <getopt.h>
 #include <stdio.h>
 #include <unistd.h>
 
@@ -18,6 +19,7 @@
 
 #include <algorithm>
 #include <memory>
+#include <map>
 #include <vector>
 
 #define BUFFER_OFFSET(i) ((char *)nullptr + (i))
@@ -30,6 +32,11 @@ 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.
+float vr_gamma = 10.0f, vr_delta = 5.0f, vr_alpha = 10.0f;
+
 // Some global OpenGL objects.
 GLuint nearest_sampler, linear_sampler, smoothness_sampler;
 GLuint vertex_vbo;
@@ -221,6 +228,58 @@ 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, enable_if<num_elements == 1> * = nullptr) {
+               render_to({{texture0}});
+       }
+
+       void render_to(GLuint texture0, GLuint texture1, enable_if<num_elements == 2> * = nullptr) {
+               render_to({{texture0, texture1}});
+       }
+
+       void render_to(GLuint texture0, GLuint texture1, GLuint texture2, enable_if<num_elements == 3> * = nullptr) {
+               render_to({{texture0, texture1, texture2}});
+       }
+
+       void render_to(GLuint texture0, GLuint texture1, GLuint texture2, GLuint texture3, enable_if<num_elements == 4> * = nullptr) {
+               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)
+{
+       auto it = fbos.find(textures);
+       if (it != fbos.end()) {
+               glBindFramebuffer(GL_FRAMEBUFFER, it->second);
+               return;
+       }
+
+       GLuint fbo;
+       glCreateFramebuffers(1, &fbo);
+       GLenum bufs[num_elements];
+       for (size_t i = 0; i < num_elements; ++i) {
+               glNamedFramebufferTexture(fbo, GL_COLOR_ATTACHMENT0 + i, textures[i], 0);
+               bufs[i] = GL_COLOR_ATTACHMENT0 + i;
+       }
+       glNamedFramebufferDrawBuffers(fbo, num_elements, bufs);
+
+       fbos[textures] = fbo;
+       glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+}
+
 // 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
@@ -235,6 +294,7 @@ public:
        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;
@@ -267,12 +327,8 @@ void Sobel::exec(GLint tex0_view, GLint grad0_tex, int level_width, int level_he
        glBindSampler(0, nearest_sampler);
        glProgramUniform1i(sobel_program, uniform_tex, 0);
 
-       GLuint grad0_fbo;  // TODO: cleanup
-       glCreateFramebuffers(1, &grad0_fbo);
-       glNamedFramebufferTexture(grad0_fbo, GL_COLOR_ATTACHMENT0, grad0_tex, 0);
-
        glViewport(0, 0, level_width, level_height);
-       glBindFramebuffer(GL_FRAMEBUFFER, grad0_fbo);
+       fbos.render_to(grad0_tex);
        glBindVertexArray(sobel_vao);
        glUseProgram(sobel_program);
        glDisable(GL_BLEND);
@@ -286,6 +342,8 @@ public:
        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;
@@ -332,12 +390,8 @@ void MotionSearch::exec(GLuint tex0_view, GLuint tex1_view, GLuint grad0_tex, GL
        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);
 
-       GLuint flow_fbo;  // TODO: cleanup
-       glCreateFramebuffers(1, &flow_fbo);
-       glNamedFramebufferTexture(flow_fbo, GL_COLOR_ATTACHMENT0, flow_out_tex, 0);
-
        glViewport(0, 0, width_patches, height_patches);
-       glBindFramebuffer(GL_FRAMEBUFFER, flow_fbo);
+       fbos.render_to(flow_out_tex);
        glBindVertexArray(motion_search_vao);
        glUseProgram(motion_search_program);
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
@@ -357,6 +411,8 @@ public:
        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;
@@ -410,15 +466,11 @@ void Densify::exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint d
                patch_spacing_x / level_width,
                patch_spacing_y / level_height);
 
-       GLuint dense_flow_fbo;  // TODO: cleanup
-       glCreateFramebuffers(1, &dense_flow_fbo);
-       glNamedFramebufferTexture(dense_flow_fbo, GL_COLOR_ATTACHMENT0, dense_flow_tex, 0);
-
        glViewport(0, 0, level_width, level_height);
        glEnable(GL_BLEND);
        glBlendFunc(GL_ONE, GL_ONE);
        glBindVertexArray(densify_vao);
-       glBindFramebuffer(GL_FRAMEBUFFER, dense_flow_fbo);
+       fbos.render_to(dense_flow_tex);
        glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width_patches * height_patches);
 }
 
@@ -436,6 +488,8 @@ public:
        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;
@@ -477,18 +531,10 @@ void Prewarp::exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint I
 
        glProgramUniform2f(prewarp_program, uniform_image_size, level_width, level_height);
 
-       GLuint prewarp_fbo;  // TODO: cleanup
-       glCreateFramebuffers(1, &prewarp_fbo);
-       GLenum bufs[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_COLOR_ATTACHMENT2 };
-       glNamedFramebufferDrawBuffers(prewarp_fbo, 3, bufs);
-       glNamedFramebufferTexture(prewarp_fbo, GL_COLOR_ATTACHMENT0, I_tex, 0);
-       glNamedFramebufferTexture(prewarp_fbo, GL_COLOR_ATTACHMENT1, I_t_tex, 0);
-       glNamedFramebufferTexture(prewarp_fbo, GL_COLOR_ATTACHMENT2, normalized_flow_tex, 0);
-
        glViewport(0, 0, level_width, level_height);
        glDisable(GL_BLEND);
        glBindVertexArray(prewarp_vao);
-       glBindFramebuffer(GL_FRAMEBUFFER, prewarp_fbo);
+       fbos.render_to(I_tex, I_t_tex, normalized_flow_tex);
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
@@ -506,6 +552,8 @@ public:
        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;
@@ -538,17 +586,10 @@ void Derivatives::exec(GLuint input_tex, GLuint I_x_y_tex, GLuint beta_0_tex, in
 
        bind_sampler(derivatives_program, uniform_tex, 0, input_tex, nearest_sampler);
 
-       GLuint derivatives_fbo;  // TODO: cleanup
-       glCreateFramebuffers(1, &derivatives_fbo);
-       GLenum bufs[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
-       glNamedFramebufferDrawBuffers(derivatives_fbo, 2, bufs);
-       glNamedFramebufferTexture(derivatives_fbo, GL_COLOR_ATTACHMENT0, I_x_y_tex, 0);
-       glNamedFramebufferTexture(derivatives_fbo, GL_COLOR_ATTACHMENT1, beta_0_tex, 0);
-
        glViewport(0, 0, level_width, level_height);
        glDisable(GL_BLEND);
        glBindVertexArray(derivatives_vao);
-       glBindFramebuffer(GL_FRAMEBUFFER, derivatives_fbo);
+       fbos.render_to(I_x_y_tex, beta_0_tex);
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
@@ -565,12 +606,15 @@ public:
        void exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint smoothness_x_tex, GLuint smoothness_y_tex, int level_width, int level_height);
 
 private:
+       PersistentFBOSet<2> fbos;
+
        GLuint smoothness_vs_obj;
        GLuint smoothness_fs_obj;
        GLuint smoothness_program;
        GLuint smoothness_vao;
 
        GLuint uniform_flow_tex, uniform_diff_flow_tex;
+       GLuint uniform_alpha;
 };
 
 ComputeSmoothness::ComputeSmoothness()
@@ -590,6 +634,7 @@ ComputeSmoothness::ComputeSmoothness()
 
        uniform_flow_tex = glGetUniformLocation(smoothness_program, "flow_tex");
        uniform_diff_flow_tex = glGetUniformLocation(smoothness_program, "diff_flow_tex");
+       uniform_alpha = glGetUniformLocation(smoothness_program, "alpha");
 }
 
 void ComputeSmoothness::exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint smoothness_x_tex, GLuint smoothness_y_tex, int level_width, int level_height)
@@ -598,19 +643,13 @@ void ComputeSmoothness::exec(GLuint flow_tex, GLuint diff_flow_tex, GLuint smoot
 
        bind_sampler(smoothness_program, uniform_flow_tex, 0, flow_tex, nearest_sampler);
        bind_sampler(smoothness_program, uniform_diff_flow_tex, 1, diff_flow_tex, nearest_sampler);
-
-       GLuint smoothness_fbo;  // TODO: cleanup
-       glCreateFramebuffers(1, &smoothness_fbo);
-       GLenum bufs[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
-       glNamedFramebufferDrawBuffers(smoothness_fbo, 2, bufs);
-       glNamedFramebufferTexture(smoothness_fbo, GL_COLOR_ATTACHMENT0, smoothness_x_tex, 0);
-       glNamedFramebufferTexture(smoothness_fbo, GL_COLOR_ATTACHMENT1, smoothness_y_tex, 0);
+       glProgramUniform1f(smoothness_program, uniform_alpha, vr_alpha);
 
        glViewport(0, 0, level_width, level_height);
 
        glDisable(GL_BLEND);
        glBindVertexArray(smoothness_vao);
-       glBindFramebuffer(GL_FRAMEBUFFER, smoothness_fbo);
+       fbos.render_to(smoothness_x_tex, smoothness_y_tex);
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 
        // Make sure the smoothness on the right and upper borders is zero.
@@ -637,6 +676,8 @@ public:
        void exec(GLuint I_x_y_tex, GLuint I_t_tex, GLuint diff_flow_tex, GLuint flow_tex, GLuint beta_0_tex, GLuint smoothness_x_tex, GLuint smoothness_y_tex, GLuint equation_tex, int level_width, int level_height);
 
 private:
+       PersistentFBOSet<1> fbos;
+
        GLuint equations_vs_obj;
        GLuint equations_fs_obj;
        GLuint equations_program;
@@ -646,6 +687,7 @@ private:
        GLuint uniform_diff_flow_tex, uniform_base_flow_tex;
        GLuint uniform_beta_0_tex;
        GLuint uniform_smoothness_x_tex, uniform_smoothness_y_tex;
+       GLuint uniform_gamma, uniform_delta;
 };
 
 SetupEquations::SetupEquations()
@@ -670,6 +712,8 @@ SetupEquations::SetupEquations()
        uniform_beta_0_tex = glGetUniformLocation(equations_program, "beta_0_tex");
        uniform_smoothness_x_tex = glGetUniformLocation(equations_program, "smoothness_x_tex");
        uniform_smoothness_y_tex = glGetUniformLocation(equations_program, "smoothness_y_tex");
+       uniform_gamma = glGetUniformLocation(equations_program, "gamma");
+       uniform_delta = glGetUniformLocation(equations_program, "delta");
 }
 
 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 smoothness_x_tex, GLuint smoothness_y_tex, GLuint equation_tex, int level_width, int level_height)
@@ -683,23 +727,18 @@ void SetupEquations::exec(GLuint I_x_y_tex, GLuint I_t_tex, GLuint diff_flow_tex
        bind_sampler(equations_program, uniform_beta_0_tex, 4, beta_0_tex, nearest_sampler);
        bind_sampler(equations_program, uniform_smoothness_x_tex, 5, smoothness_x_tex, smoothness_sampler);
        bind_sampler(equations_program, uniform_smoothness_y_tex, 6, smoothness_y_tex, smoothness_sampler);
-
-       GLuint equations_fbo;  // TODO: cleanup
-       glCreateFramebuffers(1, &equations_fbo);
-       glNamedFramebufferTexture(equations_fbo, GL_COLOR_ATTACHMENT0, equation_tex, 0);
+       glProgramUniform1f(equations_program, uniform_delta, vr_delta);
+       glProgramUniform1f(equations_program, uniform_gamma, vr_gamma);
 
        glViewport(0, 0, level_width, level_height);
        glDisable(GL_BLEND);
        glBindVertexArray(equations_vao);
-       glBindFramebuffer(GL_FRAMEBUFFER, equations_fbo);
+       fbos.render_to(equation_tex);
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
-// Calculate the smoothness constraints between neighboring pixels;
-// s_x(x,y) stores smoothness between pixel (x,y) and (x+1,y),
-// and s_y(x,y) stores between (x,y) and (x,y+1). We'll sample with
-// border color (0,0) later, so that there's zero diffusion out of
-// the border.
+// Actually solve the equation sets made by SetupEquations, by means of
+// successive over-relaxation (SOR).
 //
 // See variational_refinement.txt for more information.
 class SOR {
@@ -708,6 +747,8 @@ public:
        void exec(GLuint diff_flow_tex, GLuint equation_tex, GLuint smoothness_x_tex, GLuint smoothness_y_tex, int level_width, int level_height, int num_iterations);
 
 private:
+       PersistentFBOSet<1> fbos;
+
        GLuint sor_vs_obj;
        GLuint sor_fs_obj;
        GLuint sor_program;
@@ -748,14 +789,10 @@ void SOR::exec(GLuint diff_flow_tex, GLuint equation_tex, GLuint smoothness_x_te
        bind_sampler(sor_program, uniform_smoothness_y_tex, 2, smoothness_y_tex, smoothness_sampler);
        bind_sampler(sor_program, uniform_equation_tex, 3, equation_tex, nearest_sampler);
 
-       GLuint sor_fbo;  // TODO: cleanup
-       glCreateFramebuffers(1, &sor_fbo);
-       glNamedFramebufferTexture(sor_fbo, GL_COLOR_ATTACHMENT0, diff_flow_tex, 0);  // NOTE: Bind to same as we render from!
-
        glViewport(0, 0, level_width, level_height);
        glDisable(GL_BLEND);
        glBindVertexArray(sor_vao);
-       glBindFramebuffer(GL_FRAMEBUFFER, sor_fbo);
+       fbos.render_to(diff_flow_tex);  // NOTE: Bind to same as we render from!
 
        for (int i = 0; i < num_iterations; ++i) {
                glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
@@ -773,6 +810,8 @@ public:
        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;
@@ -805,48 +844,15 @@ void AddBaseFlow::exec(GLuint base_flow_tex, GLuint diff_flow_tex, int level_wid
 
        bind_sampler(add_flow_program, uniform_diff_flow_tex, 0, diff_flow_tex, nearest_sampler);
 
-       GLuint add_flow_fbo;  // TODO: cleanup
-       glCreateFramebuffers(1, &add_flow_fbo);
-       glNamedFramebufferTexture(add_flow_fbo, GL_COLOR_ATTACHMENT0, base_flow_tex, 0);
-
        glViewport(0, 0, level_width, level_height);
        glEnable(GL_BLEND);
        glBlendFunc(GL_ONE, GL_ONE);
        glBindVertexArray(add_flow_vao);
-       glBindFramebuffer(GL_FRAMEBUFFER, add_flow_fbo);
+       fbos.render_to(base_flow_tex);
 
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
-class GPUTimers {
-public:
-       void print();
-       pair<GLuint, GLuint> begin_timer(const string &name, int level);
-
-private:
-       struct Timer {
-               string name;
-               int level;
-               pair<GLuint, GLuint> query;
-       };
-       vector<Timer> timers;
-};
-
-pair<GLuint, GLuint> GPUTimers::begin_timer(const string &name, int level)
-{
-       GLuint queries[2];
-       glGenQueries(2, queries);
-       glQueryCounter(queries[0], GL_TIMESTAMP);
-
-       Timer timer;
-       timer.name = name;
-       timer.level = level;
-       timer.query.first = queries[0];
-       timer.query.second = queries[1];
-       timers.push_back(timer);
-       return timer.query;
-}
-
 // Take a copy of the flow, bilinearly interpolated and scaled up.
 class ResizeFlow {
 public:
@@ -854,6 +860,8 @@ public:
        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;
@@ -890,18 +898,43 @@ void ResizeFlow::exec(GLuint flow_tex, GLuint out_tex, int input_width, int inpu
 
        glProgramUniform2f(resize_flow_program, uniform_scale_factor, float(output_width) / input_width, float(output_height) / input_height);
 
-       GLuint resize_flow_fbo;  // TODO: cleanup
-       glCreateFramebuffers(1, &resize_flow_fbo);
-       glNamedFramebufferTexture(resize_flow_fbo, GL_COLOR_ATTACHMENT0, out_tex, 0);
-
        glViewport(0, 0, output_width, output_height);
        glDisable(GL_BLEND);
        glBindVertexArray(resize_flow_vao);
-       glBindFramebuffer(GL_FRAMEBUFFER, resize_flow_fbo);
+       fbos.render_to(out_tex);
 
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
+class GPUTimers {
+public:
+       void print();
+       pair<GLuint, GLuint> begin_timer(const string &name, int level);
+
+private:
+       struct Timer {
+               string name;
+               int level;
+               pair<GLuint, GLuint> query;
+       };
+       vector<Timer> timers;
+};
+
+pair<GLuint, GLuint> GPUTimers::begin_timer(const string &name, int level)
+{
+       GLuint queries[2];
+       glGenQueries(2, queries);
+       glQueryCounter(queries[0], GL_TIMESTAMP);
+
+       Timer timer;
+       timer.name = name;
+       timer.level = level;
+       timer.query.first = queries[0];
+       timer.query.second = queries[1];
+       timers.push_back(timer);
+       return timer.query;
+}
+
 void GPUTimers::print()
 {
        for (const Timer &timer : timers) {
@@ -913,7 +946,7 @@ void GPUTimers::print()
                for (int i = 0; i < timer.level * 2; ++i) {
                        fprintf(stderr, " ");
                }
-               fprintf(stderr, "%-30s %4.1f ms\n", timer.name.c_str(), (time_end - time_start) / 1e6);
+               fprintf(stderr, "%-30s %4.1f ms\n", timer.name.c_str(), GLint64(time_end - time_start) / 1e6);
        }
 }
 
@@ -955,6 +988,35 @@ private:
 
 int main(int argc, char **argv)
 {
+        static const option long_options[] = {
+                { "alpha", required_argument, 0, 'a' },
+                { "delta", required_argument, 0, 'd' },
+                { "gamma", required_argument, 0, 'g' }
+       };
+
+       for ( ;; ) {
+               int option_index = 0;
+               int c = getopt_long(argc, argv, "a:d:g:", long_options, &option_index);
+
+               if (c == -1) {
+                       break;
+               }
+               switch (c) {
+               case 'a':
+                       vr_alpha = atof(optarg);
+                       break;
+               case 'd':
+                       vr_delta = atof(optarg);
+                       break;
+               case 'g':
+                       vr_gamma = atof(optarg);
+                       break;
+               default:
+                       fprintf(stderr, "Unknown option '%s'\n", argv[option_index]);
+                       exit(1);
+               };
+       }
+
        if (SDL_Init(SDL_INIT_EVERYTHING) == -1) {
                fprintf(stderr, "SDL_Init failed: %s\n", SDL_GetError());
                exit(1);
@@ -978,8 +1040,8 @@ int main(int argc, char **argv)
 
        // Load pictures.
        unsigned width1, height1, width2, height2;
-       GLuint tex0 = load_texture(argc >= 2 ? argv[1] : "test1499.png", &width1, &height1);
-       GLuint tex1 = load_texture(argc >= 3 ? argv[2] : "test1500.png", &width2, &height2);
+       GLuint tex0 = load_texture(argc >= (optind + 1) ? argv[optind] : "test1499.png", &width1, &height1);
+       GLuint tex1 = load_texture(argc >= (optind + 2) ? argv[optind + 1] : "test1500.png", &width2, &height2);
 
        if (width1 != width2 || height1 != height2) {
                fprintf(stderr, "Image dimensions don't match (%dx%d versus %dx%d)\n",
@@ -1024,6 +1086,7 @@ int main(int argc, char **argv)
        GLuint initial_flow_tex;
        glCreateTextures(GL_TEXTURE_2D, 1, &initial_flow_tex);
        glTextureStorage2D(initial_flow_tex, 1, GL_RG16F, 1, 1);
+       glClearTexImage(initial_flow_tex, 0, GL_RG, GL_FLOAT, nullptr);
        int prev_level_width = 1, prev_level_height = 1;
 
        GLuint prev_level_flow_tex = initial_flow_tex;