]> git.sesse.net Git - movit/blobdiff - resample_effect.cpp
Compute version of ResampleEffect.
[movit] / resample_effect.cpp
index 9b6d5f3d4d964168d0a4a0f191e8552b1f54217d..74508646091872aec75b020b7dfa60d0639ae125 100644 (file)
@@ -1,7 +1,7 @@
 // Three-lobed Lanczos, the most common choice.
 // Note that if you change this, the accuracy for LANCZOS_TABLE_SIZE
 // needs to be recomputed.
-#define LANCZOS_RADIUS 3.0
+#define LANCZOS_RADIUS 3.0f
 
 #include <epoxy/gl.h>
 #include <assert.h>
@@ -9,6 +9,7 @@
 #include <math.h>
 #include <stdio.h>
 #include <algorithm>
+#include <mutex>
 #include <Eigen/Sparse>
 #include <Eigen/SparseQR>
 #include <Eigen/OrderingMethods>
@@ -72,7 +73,7 @@ float lanczos_weight(float x)
 // You need to call lanczos_table_init_done before the first call to
 // lanczos_weight_cached.
 #define LANCZOS_TABLE_SIZE 2048
-bool lanczos_table_init_done = false;
+static once_flag lanczos_table_init_done;
 float lanczos_table[LANCZOS_TABLE_SIZE + 2];
 
 void init_lanczos_table()
@@ -80,7 +81,6 @@ void init_lanczos_table()
        for (unsigned i = 0; i < LANCZOS_TABLE_SIZE + 2; ++i) {
                lanczos_table[i] = lanczos_weight(float(i) * (LANCZOS_RADIUS / LANCZOS_TABLE_SIZE));
        }
-       lanczos_table_init_done = true;
 }
 
 float lanczos_weight_cached(float x)
@@ -90,7 +90,7 @@ float lanczos_weight_cached(float x)
                return 0.0f;
        }
        float table_pos = x * (LANCZOS_TABLE_SIZE / LANCZOS_RADIUS);
-       int table_pos_int = int(table_pos);  // Truncate towards zero.
+       unsigned table_pos_int = int(table_pos);  // Truncate towards zero.
        float table_pos_frac = table_pos - table_pos_int;
        assert(table_pos < LANCZOS_TABLE_SIZE + 2);
        return lanczos_table[table_pos_int] +
@@ -109,7 +109,7 @@ unsigned gcd(unsigned a, unsigned b)
 }
 
 template<class DestFloat>
-unsigned combine_samples(const Tap<float> *src, Tap<DestFloat> *dst, float num_subtexels, float inv_num_subtexels, unsigned num_src_samples, unsigned max_samples_saved)
+unsigned combine_samples(const Tap<float> *src, Tap<DestFloat> *dst, float num_subtexels, float inv_num_subtexels, unsigned num_src_samples, unsigned max_samples_saved, float pos1_pos2_diff, float inv_pos1_pos2_diff)
 {
        // Cut off near-zero values at both sides.
        unsigned num_samples_saved = 0;
@@ -129,7 +129,7 @@ unsigned combine_samples(const Tap<float> *src, Tap<DestFloat> *dst, float num_s
 
        for (unsigned i = 0, j = 0; i < num_src_samples; ++i, ++j) {
                // Copy the sample directly; it will be overwritten later if we can combine.
-               if (dst != NULL) {
+               if (dst != nullptr) {
                        dst[j].weight = convert_float<float, DestFloat>(src[i].weight);
                        dst[j].pos = convert_float<float, DestFloat>(src[i].pos);
                }
@@ -157,7 +157,7 @@ unsigned combine_samples(const Tap<float> *src, Tap<DestFloat> *dst, float num_s
 
                DestFloat pos, total_weight;
                float sum_sq_error;
-               combine_two_samples(w1, w2, pos1, pos2, num_subtexels, inv_num_subtexels, &pos, &total_weight, &sum_sq_error);
+               combine_two_samples(w1, w2, pos1, pos1_pos2_diff, inv_pos1_pos2_diff, num_subtexels, inv_num_subtexels, &pos, &total_weight, &sum_sq_error);
 
                // If the interpolation error is larger than that of about sqrt(2) of
                // a level at 8-bit precision, don't combine. (You'd think 1.0 was enough,
@@ -169,7 +169,7 @@ unsigned combine_samples(const Tap<float> *src, Tap<DestFloat> *dst, float num_s
                }
 
                // OK, we can combine this and the next sample.
-               if (dst != NULL) {
+               if (dst != nullptr) {
                        dst[j].weight = total_weight;
                        dst[j].pos = pos;
                }
@@ -197,6 +197,21 @@ void normalize_sum(Tap<T>* vals, unsigned num)
        }
 }
 
+template<class T>
+void normalize_sum(T* vals, unsigned num)
+{
+       for (int normalize_pass = 0; normalize_pass < 2; ++normalize_pass) {
+               float sum = 0.0;
+               for (unsigned i = 0; i < num; ++i) {
+                       sum += to_fp32(vals[i]);
+               }
+               float inv_sum = 1.0 / sum;
+               for (unsigned i = 0; i < num; ++i) {
+                       vals[i] = from_fp32<T>(to_fp32(vals[i]) * inv_sum);
+               }
+       }
+}
+
 // Make use of the bilinear filtering in the GPU to reduce the number of samples
 // we need to make. This is a bit more complex than BlurEffect since we cannot combine
 // two neighboring samples if their weights have differing signs, so we first need to
@@ -210,10 +225,12 @@ unsigned combine_many_samples(const Tap<float> *weights, unsigned src_size, unsi
 {
        float num_subtexels = src_size / movit_texel_subpixel_precision;
        float inv_num_subtexels = movit_texel_subpixel_precision / src_size;
+       float pos1_pos2_diff = 1.0f / src_size;
+       float inv_pos1_pos2_diff = src_size;
 
        unsigned max_samples_saved = UINT_MAX;
        for (unsigned y = 0; y < dst_samples && max_samples_saved > 0; ++y) {
-               unsigned num_samples_saved = combine_samples<DestFloat>(weights + y * src_samples, NULL, num_subtexels, inv_num_subtexels, src_samples, max_samples_saved);
+               unsigned num_samples_saved = combine_samples<DestFloat>(weights + y * src_samples, nullptr, num_subtexels, inv_num_subtexels, src_samples, max_samples_saved, pos1_pos2_diff, inv_pos1_pos2_diff);
                max_samples_saved = min(max_samples_saved, num_samples_saved);
        }
 
@@ -228,7 +245,9 @@ unsigned combine_many_samples(const Tap<float> *weights, unsigned src_size, unsi
                        num_subtexels,
                        inv_num_subtexels,
                        src_samples,
-                       max_samples_saved);
+                       max_samples_saved,
+                       pos1_pos2_diff,
+                       inv_pos1_pos2_diff);
                assert(num_samples_saved == max_samples_saved);
                normalize_sum(bilinear_weights_ptr, src_bilinear_samples);
        }
@@ -249,10 +268,10 @@ double compute_sum_sq_error(const Tap<float>* weights, unsigned num_weights,
        // Find the effective range of the bilinear-optimized kernel.
        // Due to rounding of the positions, this is not necessarily the same
        // as the intended range (ie., the range of the original weights).
-       int lower_pos = int(floor(to_fp32(bilinear_weights[0].pos) * size - 0.5));
-       int upper_pos = int(ceil(to_fp32(bilinear_weights[num_bilinear_weights - 1].pos) * size - 0.5)) + 2;
-       lower_pos = min<int>(lower_pos, lrintf(weights[0].pos * size - 0.5));
-       upper_pos = max<int>(upper_pos, lrintf(weights[num_weights - 1].pos * size - 0.5) + 1);
+       int lower_pos = int(floor(to_fp32(bilinear_weights[0].pos) * size - 0.5f));
+       int upper_pos = int(ceil(to_fp32(bilinear_weights[num_bilinear_weights - 1].pos) * size - 0.5f)) + 2;
+       lower_pos = min<int>(lower_pos, lrintf(weights[0].pos * size - 0.5f));
+       upper_pos = max<int>(upper_pos, lrintf(weights[num_weights - 1].pos * size - 0.5f) + 1);
 
        float* effective_weights = new float[upper_pos - lower_pos];
        for (int i = 0; i < upper_pos - lower_pos; ++i) {
@@ -271,7 +290,7 @@ double compute_sum_sq_error(const Tap<float>* weights, unsigned num_weights,
                assert(x0 < upper_pos - lower_pos);
                assert(x1 < upper_pos - lower_pos);
 
-               effective_weights[x0] += to_fp32(bilinear_weights[i].weight) * (1.0 - f);
+               effective_weights[x0] += to_fp32(bilinear_weights[i].weight) * (1.0f - f);
                effective_weights[x1] += to_fp32(bilinear_weights[i].weight) * f;
        }
 
@@ -305,22 +324,40 @@ ResampleEffect::ResampleEffect()
        register_int("width", &output_width);
        register_int("height", &output_height);
 
-       // The first blur pass will forward resolution information to us.
-       hpass = new SingleResamplePassEffect(this);
-       CHECK(hpass->set_int("direction", SingleResamplePassEffect::HORIZONTAL));
-       vpass = new SingleResamplePassEffect(NULL);
-       CHECK(vpass->set_int("direction", SingleResamplePassEffect::VERTICAL));
+       if (movit_compute_shaders_supported) {
+               // The effect will forward resolution information to us.
+               compute_effect_owner.reset(new ResampleComputeEffect(this));
+               compute_effect = compute_effect_owner.get();
+       } else {
+               // The first blur pass will forward resolution information to us.
+               hpass_owner.reset(new SingleResamplePassEffect(this));
+               hpass = hpass_owner.get();
+               CHECK(hpass->set_int("direction", SingleResamplePassEffect::HORIZONTAL));
+               vpass_owner.reset(new SingleResamplePassEffect(this));
+               vpass = vpass_owner.get();
+               CHECK(vpass->set_int("direction", SingleResamplePassEffect::VERTICAL));
+       }
 
        update_size();
 }
 
+ResampleEffect::~ResampleEffect()
+{
+}
+
 void ResampleEffect::rewrite_graph(EffectChain *graph, Node *self)
 {
-       Node *hpass_node = graph->add_node(hpass);
-       Node *vpass_node = graph->add_node(vpass);
-       graph->connect_nodes(hpass_node, vpass_node);
-       graph->replace_receiver(self, hpass_node);
-       graph->replace_sender(self, vpass_node);
+       if (compute_effect != nullptr) {
+               Node *compute_node = graph->add_node(compute_effect_owner.release());
+               graph->replace_receiver(self, compute_node);
+               graph->replace_sender(self, compute_node);
+       } else {
+               Node *hpass_node = graph->add_node(hpass_owner.release());
+               Node *vpass_node = graph->add_node(vpass_owner.release());
+               graph->connect_nodes(hpass_node, vpass_node);
+               graph->replace_receiver(self, hpass_node);
+               graph->replace_sender(self, vpass_node);
+       }
        self->disabled = true;
 } 
 
@@ -339,16 +376,22 @@ void ResampleEffect::inform_input_size(unsigned input_num, unsigned width, unsig
 void ResampleEffect::update_size()
 {
        bool ok = true;
-       ok |= hpass->set_int("input_width", input_width);
-       ok |= hpass->set_int("input_height", input_height);
-       ok |= hpass->set_int("output_width", output_width);
-       ok |= hpass->set_int("output_height", input_height);
-
-       ok |= vpass->set_int("input_width", output_width);
-       ok |= vpass->set_int("input_height", input_height);
-       ok |= vpass->set_int("output_width", output_width);
-       ok |= vpass->set_int("output_height", output_height);
+       if (compute_effect != nullptr) {
+               ok |= compute_effect->set_int("input_width", input_width);
+               ok |= compute_effect->set_int("input_height", input_height);
+               ok |= compute_effect->set_int("output_width", output_width);
+               ok |= compute_effect->set_int("output_height", output_height);
+       } else {
+               ok |= hpass->set_int("input_width", input_width);
+               ok |= hpass->set_int("input_height", input_height);
+               ok |= hpass->set_int("output_width", output_width);
+               ok |= hpass->set_int("output_height", input_height);
 
+               ok |= vpass->set_int("input_width", output_width);
+               ok |= vpass->set_int("input_height", input_height);
+               ok |= vpass->set_int("output_width", output_width);
+               ok |= vpass->set_int("output_height", output_height);
+       }
        assert(ok);
 
        // The offset added due to zoom may have changed with the size.
@@ -364,10 +407,17 @@ void ResampleEffect::update_offset_and_zoom()
        float extra_offset_x = zoom_center_x * (1.0f - 1.0f / zoom_x) * input_width;
        float extra_offset_y = (1.0f - zoom_center_y) * (1.0f - 1.0f / zoom_y) * input_height;
 
-       ok |= hpass->set_float("offset", extra_offset_x + offset_x);
-       ok |= vpass->set_float("offset", extra_offset_y - offset_y);  // Compensate for the bottom-left origin.
-       ok |= hpass->set_float("zoom", zoom_x);
-       ok |= vpass->set_float("zoom", zoom_y);
+       if (compute_effect != nullptr) {
+               ok |= compute_effect->set_float("offset_x", extra_offset_x + offset_x);
+               ok |= compute_effect->set_float("offset_y", extra_offset_y - offset_y);  // Compensate for the bottom-left origin.
+               ok |= compute_effect->set_float("zoom_x", zoom_x);
+               ok |= compute_effect->set_float("zoom_y", zoom_y);
+       } else {
+               ok |= hpass->set_float("offset", extra_offset_x + offset_x);
+               ok |= vpass->set_float("offset", extra_offset_y - offset_y);  // Compensate for the bottom-left origin.
+               ok |= hpass->set_float("zoom", zoom_x);
+               ok |= vpass->set_float("zoom", zoom_y);
+       }
 
        assert(ok);
 }
@@ -425,8 +475,8 @@ bool ResampleEffect::set_float(const string &key, float value) {
 SingleResamplePassEffect::SingleResamplePassEffect(ResampleEffect *parent)
        : parent(parent),
          direction(HORIZONTAL),
-         input_width(1280),
-         input_height(720),
+         input_width(1280),
+         input_height(720),
          offset(0.0),
          zoom(1.0),
          last_input_width(-1),
@@ -434,8 +484,7 @@ SingleResamplePassEffect::SingleResamplePassEffect(ResampleEffect *parent)
          last_output_width(-1),
          last_output_height(-1),
          last_offset(0.0 / 0.0),  // NaN.
-         last_zoom(0.0 / 0.0),  // NaN.
-         last_texture_width(-1), last_texture_height(-1)
+         last_zoom(0.0 / 0.0)  // NaN.
 {
        register_int("direction", (int *)&direction);
        register_int("input_width", &input_width);
@@ -452,18 +501,11 @@ SingleResamplePassEffect::SingleResamplePassEffect(ResampleEffect *parent)
        register_uniform_float("sample_x_offset", &uniform_sample_x_offset);
        register_uniform_float("whole_pixel_offset", &uniform_whole_pixel_offset);
 
-       glGenTextures(1, &texnum);
-
-       if (!lanczos_table_init_done) {
-               // Could in theory race between two threads if we are unlucky,
-               // but that is harmless, since they'll write the same data.
-               init_lanczos_table();
-       }
+       call_once(lanczos_table_init_done, init_lanczos_table);
 }
 
 SingleResamplePassEffect::~SingleResamplePassEffect()
 {
-       glDeleteTextures(1, &texnum);
 }
 
 string SingleResamplePassEffect::output_fragment_shader()
@@ -500,7 +542,7 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const str
                assert(false);
        }
 
-       ScalingWeights weights = calculate_scaling_weights(src_size, dst_size, zoom, offset);
+       ScalingWeights weights = calculate_bilinear_scaling_weights(src_size, dst_size, zoom, offset, BilinearFormatConstraints::ALLOW_FP16_AND_FP32);
        src_bilinear_samples = weights.src_bilinear_samples;
        num_loops = weights.num_loops;
        slice_height = 1.0f / weights.num_loops;
@@ -508,17 +550,8 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const str
        // Encode as a two-component texture. Note the GL_REPEAT.
        glActiveTexture(GL_TEXTURE0 + *sampler_num);
        check_error();
-       glBindTexture(GL_TEXTURE_2D, texnum);
+       glBindTexture(GL_TEXTURE_2D, tex.get_texnum());
        check_error();
-       if (last_texture_width == -1) {
-               // Need to set this state the first time.
-               glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
-               check_error();
-               glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
-               check_error();
-               glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
-               check_error();
-       }
 
        GLenum type, internal_format;
        void *pixels;
@@ -533,27 +566,115 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const str
                pixels = weights.bilinear_weights_fp16.get();
        }
 
-       if (int(weights.src_bilinear_samples) == last_texture_width &&
-           int(weights.dst_samples) == last_texture_height &&
-           internal_format == last_texture_internal_format) {
-               // Texture dimensions and type are unchanged; it is more efficient
-               // to just update it rather than making an entirely new texture.
-               glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, weights.src_bilinear_samples, weights.dst_samples, GL_RG, type, pixels);
-       } else {
-               glTexImage2D(GL_TEXTURE_2D, 0, internal_format, weights.src_bilinear_samples, weights.dst_samples, 0, GL_RG, type, pixels);
-               last_texture_width = weights.src_bilinear_samples;
-               last_texture_height = weights.dst_samples;
-               last_texture_internal_format = internal_format;
-       }
+       tex.update(weights.src_bilinear_samples, weights.dst_samples, internal_format, GL_RG, type, pixels);
+}
+
+ResampleComputeEffect::ResampleComputeEffect(ResampleEffect *parent)
+       : parent(parent),
+         input_width(1280),
+         input_height(720),
+         offset_x(0.0),
+         offset_y(0.0),
+         zoom_x(1.0),
+         zoom_y(1.0),
+         last_input_width(-1),
+         last_input_height(-1),
+         last_output_width(-1),
+         last_output_height(-1),
+         last_offset_x(0.0 / 0.0),  // NaN.
+         last_offset_y(0.0 / 0.0),  // NaN.
+         last_zoom_x(0.0 / 0.0),  // NaN.
+         last_zoom_y(0.0 / 0.0)  // NaN.
+{
+       register_int("input_width", &input_width);
+       register_int("input_height", &input_height);
+       register_int("output_width", &output_width);
+       register_int("output_height", &output_height);
+       register_float("offset_x", &offset_x);
+       register_float("offset_y", &offset_y);
+       register_float("zoom_x", &zoom_x);
+       register_float("zoom_y", &zoom_y);
+       register_uniform_sampler2d("sample_tex_horizontal", &uniform_sample_tex_horizontal);
+       register_uniform_sampler2d("sample_tex_vertical", &uniform_sample_tex_vertical);
+       register_uniform_int("num_horizontal_samples", &uniform_num_horizontal_samples);
+       register_uniform_int("num_vertical_samples", &uniform_num_vertical_samples);
+       register_uniform_int("vertical_int_radius", &uniform_vertical_int_radius);
+       register_uniform_float("inv_vertical_scaling_factor", &uniform_inv_vertical_scaling_factor);
+       register_uniform_int("output_samples_per_block", &uniform_output_samples_per_block);
+       register_uniform_int("num_horizontal_filters", &uniform_num_horizontal_filters);
+       register_uniform_int("num_vertical_filters", &uniform_num_vertical_filters);
+       register_uniform_float("slice_height", &uniform_slice_height);
+       register_uniform_float("horizontal_whole_pixel_offset", &uniform_horizontal_whole_pixel_offset);
+       register_uniform_int("vertical_whole_pixel_offset", &uniform_vertical_whole_pixel_offset);
+       register_uniform_float("inv_input_height", &uniform_inv_input_height);
+       register_uniform_float("input_texcoord_y_adjust", &uniform_input_texcoord_y_adjust);
+
+       call_once(lanczos_table_init_done, init_lanczos_table);
+}
+
+ResampleComputeEffect::~ResampleComputeEffect()
+{
+}
+
+string ResampleComputeEffect::output_fragment_shader()
+{
+       char buf[256] = "";
+       return buf + read_file("resample_effect.comp");
+}
+
+// The compute shader does horizontal scaling first, using exactly the same
+// two-component texture format as in the two-pass version (see the comments
+// on ResampleComputeEffect). The vertical scaling calculates the offset values
+// in the shader, so we only store a one-component texture with the weights
+// for each filter.
+void ResampleComputeEffect::update_texture(GLuint glsl_program_num, const string &prefix, unsigned *sampler_num)
+{
+       ScalingWeights horiz_weights = calculate_bilinear_scaling_weights(input_width, output_width, zoom_x, offset_x, BilinearFormatConstraints::ALLOW_FP32_ONLY);
+       ScalingWeights vert_weights = calculate_raw_scaling_weights(input_height, output_height, zoom_y, offset_y);
+       uniform_vertical_int_radius = vert_weights.int_radius;
+       vertical_scaling_factor = vert_weights.scaling_factor;
+       uniform_inv_vertical_scaling_factor = 1.0f / vert_weights.scaling_factor;
+       src_horizontal_bilinear_samples = horiz_weights.src_bilinear_samples;
+       src_vertical_samples = vert_weights.src_bilinear_samples;
+       uniform_num_horizontal_filters = horiz_weights.dst_samples;
+       uniform_num_vertical_filters = vert_weights.dst_samples;
+       slice_height = 1.0f / horiz_weights.num_loops;
+
+       // Encode as a two-component texture. Note the GL_REPEAT.
+       glActiveTexture(GL_TEXTURE0 + *sampler_num);
+       check_error();
+       glBindTexture(GL_TEXTURE_2D, tex_horiz.get_texnum());
+       check_error();
+
+       tex_horiz.update(horiz_weights.src_bilinear_samples, horiz_weights.dst_samples, GL_RG32F, GL_RG, GL_FLOAT, horiz_weights.bilinear_weights_fp32.get());
+
+       glActiveTexture(GL_TEXTURE0 + *sampler_num + 1);
+       check_error();
+       glBindTexture(GL_TEXTURE_2D, tex_vert.get_texnum());
        check_error();
+
+       // Storing the vertical weights as fp16 instead of fp32 saves a few
+       // percent on NVIDIA, and it doesn't seem to hurt quality any.
+       // (The horizontal weights is a different story, since the offsets
+       // can get large and are fairly accuracy-sensitive. Also, they are
+       // loaded only once per workgroup, at the very beginning.)
+       tex_vert.update(vert_weights.src_bilinear_samples, vert_weights.dst_samples, GL_R16F, GL_RED, GL_HALF_FLOAT, vert_weights.raw_weights.get());
+
+       // Figure out how many output samples each compute shader block is going to output.
+       int usable_input_samples_per_block = 128 - 2 * uniform_vertical_int_radius;
+       int output_samples_per_block = int(floor(usable_input_samples_per_block * vertical_scaling_factor));
+       if (output_samples_per_block < 1) {
+               output_samples_per_block = 1;
+       }
+       uniform_output_samples_per_block = output_samples_per_block;
 }
 
+namespace {
+
 ScalingWeights calculate_scaling_weights(unsigned src_size, unsigned dst_size, float zoom, float offset)
 {
-       if (!lanczos_table_init_done) {
-               // Only needed if run from outside ResampleEffect.
-               init_lanczos_table();
-       }
+       // Only needed if run from outside ResampleEffect.
+       call_once(lanczos_table_init_done, init_lanczos_table);
 
        // For many resamplings (e.g. 640 -> 1280), we will end up with the same
        // set of samples over and over again in a loop. Thus, we can compute only
@@ -626,60 +747,107 @@ ScalingWeights calculate_scaling_weights(unsigned src_size, unsigned dst_size, f
        // to compute the destination pixel, and how many depend on the scaling factor.
        // Thus, the kernel width will vary with how much we scale.
        float radius_scaling_factor = min(scaling_factor, 1.0f);
-       int int_radius = lrintf(LANCZOS_RADIUS / radius_scaling_factor);
-       int src_samples = int_radius * 2 + 1;
+       const int int_radius = lrintf(LANCZOS_RADIUS / radius_scaling_factor);
+       const int src_samples = int_radius * 2 + 1;
        unique_ptr<Tap<float>[]> weights(new Tap<float>[dst_samples * src_samples]);
        float subpixel_offset = offset - lrintf(offset);  // The part not covered by whole_pixel_offset.
        assert(subpixel_offset >= -0.5f && subpixel_offset <= 0.5f);
+       float inv_scaling_factor = 1.0f / scaling_factor;
        for (unsigned y = 0; y < dst_samples; ++y) {
                // Find the point around which we want to sample the source image,
                // compensating for differing pixel centers as the scale changes.
-               float center_src_y = (y + 0.5f) scaling_factor - 0.5f;
+               float center_src_y = (y + 0.5f) * inv_scaling_factor - 0.5f;
                int base_src_y = lrintf(center_src_y);
 
                // Now sample <int_radius> pixels on each side around that point.
+               float inv_src_size = 1.0 / float(src_size);
                for (int i = 0; i < src_samples; ++i) {
                        int src_y = base_src_y + i - int_radius;
                        float weight = lanczos_weight_cached(radius_scaling_factor * (src_y - center_src_y - subpixel_offset));
                        weights[y * src_samples + i].weight = weight * radius_scaling_factor;
-                       weights[y * src_samples + i].pos = (src_y + 0.5) / float(src_size);
+                       weights[y * src_samples + i].pos = (src_y + 0.5f) * inv_src_size;
                }
        }
 
+       ScalingWeights ret;
+       ret.src_bilinear_samples = src_samples;
+       ret.dst_samples = dst_samples;
+       ret.int_radius = int_radius;
+       ret.scaling_factor = scaling_factor;
+       ret.num_loops = num_loops;
+       ret.bilinear_weights_fp16 = nullptr;
+       ret.bilinear_weights_fp32 = move(weights);
+       ret.raw_weights = nullptr;
+       return ret;
+}
+
+}  // namespace
+
+ScalingWeights calculate_bilinear_scaling_weights(unsigned src_size, unsigned dst_size, float zoom, float offset, BilinearFormatConstraints constraints)
+{
+       ScalingWeights ret = calculate_scaling_weights(src_size, dst_size, zoom, offset);
+       unique_ptr<Tap<float>[]> weights = move(ret.bilinear_weights_fp32);
+       const int src_samples = ret.src_bilinear_samples;
+
        // Now make use of the bilinear filtering in the GPU to reduce the number of samples
        // we need to make. Try fp16 first; if it's not accurate enough, we go to fp32.
        // Our tolerance level for total error is a bit higher than the one for invididual
        // samples, since one would assume overall errors in the shape don't matter as much.
        const float max_error = 2.0f / (255.0f * 255.0f);
        unique_ptr<Tap<fp16_int_t>[]> bilinear_weights_fp16;
-       int src_bilinear_samples = combine_many_samples(weights.get(), src_size, src_samples, dst_samples, &bilinear_weights_fp16);
-       unique_ptr<Tap<float>[]> bilinear_weights_fp32 = NULL;
+       unique_ptr<Tap<float>[]> bilinear_weights_fp32;
        double max_sum_sq_error_fp16 = 0.0;
-       for (unsigned y = 0; y < dst_samples; ++y) {
-               double sum_sq_error_fp16 = compute_sum_sq_error(
-                       weights.get() + y * src_samples, src_samples,
-                       bilinear_weights_fp16.get() + y * src_bilinear_samples, src_bilinear_samples,
-                       src_size);
-               max_sum_sq_error_fp16 = std::max(max_sum_sq_error_fp16, sum_sq_error_fp16);
-               if (max_sum_sq_error_fp16 > max_error) {
-                       break;
+       int src_bilinear_samples;
+       if (constraints == BilinearFormatConstraints::ALLOW_FP32_ONLY) {
+               max_sum_sq_error_fp16 = numeric_limits<double>::max();
+       } else {
+               assert(constraints == BilinearFormatConstraints::ALLOW_FP16_AND_FP32);
+               src_bilinear_samples = combine_many_samples(weights.get(), src_size, src_samples, ret.dst_samples, &bilinear_weights_fp16);
+               for (unsigned y = 0; y < ret.dst_samples; ++y) {
+                       double sum_sq_error_fp16 = compute_sum_sq_error(
+                               weights.get() + y * src_samples, src_samples,
+                               bilinear_weights_fp16.get() + y * src_bilinear_samples, src_bilinear_samples,
+                               src_size);
+                       max_sum_sq_error_fp16 = std::max(max_sum_sq_error_fp16, sum_sq_error_fp16);
+                       if (max_sum_sq_error_fp16 > max_error) {
+                               break;
+                       }
                }
        }
 
        if (max_sum_sq_error_fp16 > max_error) {
                bilinear_weights_fp16.reset();
-               src_bilinear_samples = combine_many_samples(weights.get(), src_size, src_samples, dst_samples, &bilinear_weights_fp32);
+               src_bilinear_samples = combine_many_samples(weights.get(), src_size, src_samples, ret.dst_samples, &bilinear_weights_fp32);
        }
 
-       ScalingWeights ret;
        ret.src_bilinear_samples = src_bilinear_samples;
-       ret.dst_samples = dst_samples;
-       ret.num_loops = num_loops;
        ret.bilinear_weights_fp16 = move(bilinear_weights_fp16);
        ret.bilinear_weights_fp32 = move(bilinear_weights_fp32);
        return ret;
 }
 
+// Unlike calculate_bilinear_scaling_weights(), this just converts the weights,
+// without any combining trickery. Thus, it is also much faster.
+ScalingWeights calculate_raw_scaling_weights(unsigned src_size, unsigned dst_size, float zoom, float offset)
+{
+       ScalingWeights ret = calculate_scaling_weights(src_size, dst_size, zoom, offset);
+       unique_ptr<Tap<float>[]> weights = move(ret.bilinear_weights_fp32);
+       const int src_samples = ret.src_bilinear_samples;
+
+       // Convert to fp16 (without any positions, as they are calculated implicitly
+       // by the compute shader) and normalize.
+       unique_ptr<fp16_int_t[]> raw_weights(new fp16_int_t[ret.dst_samples * src_samples]);
+       for (unsigned y = 0; y < ret.dst_samples; ++y) {
+               for (int i = 0; i < src_samples; ++i) {
+                       raw_weights[y * src_samples + i] = fp32_to_fp16(weights[y * src_samples + i].weight);
+               }
+               normalize_sum(raw_weights.get() + y * src_samples, src_samples);
+       }
+
+       ret.raw_weights = move(raw_weights);
+       return ret;
+}
+
 void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const string &prefix, unsigned *sampler_num)
 {
        Effect::set_gl_state(glsl_program_num, prefix, sampler_num);
@@ -706,7 +874,7 @@ void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const strin
 
        glActiveTexture(GL_TEXTURE0 + *sampler_num);
        check_error();
-       glBindTexture(GL_TEXTURE_2D, texnum);
+       glBindTexture(GL_TEXTURE_2D, tex.get_texnum());
        check_error();
 
        uniform_sample_tex = *sampler_num;
@@ -724,16 +892,107 @@ void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const strin
        } else {
                uniform_whole_pixel_offset = lrintf(offset) / float(input_width);
        }
+}
 
-       // We specifically do not want mipmaps on the input texture;
-       // they break minification.
-       Node *self = chain->find_node_for_effect(this);
-       if (chain->has_input_sampler(self, 0)) {
-               glActiveTexture(chain->get_input_sampler(self, 0));
+Support2DTexture::Support2DTexture()
+{
+       glGenTextures(1, &texnum);
+       check_error();
+       glBindTexture(GL_TEXTURE_2D, texnum);
+       check_error();
+       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+       check_error();
+       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
+       check_error();
+       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
+       check_error();
+}
+
+Support2DTexture::~Support2DTexture()
+{
+       glDeleteTextures(1, &texnum);
+       check_error();
+}
+
+void Support2DTexture::update(GLint width, GLint height, GLenum internal_format, GLenum format, GLenum type, const GLvoid * data)
+{
+       glBindTexture(GL_TEXTURE_2D, texnum);
+       check_error();
+       if (width == last_texture_width &&
+           height == last_texture_height &&
+           internal_format == last_texture_internal_format) {
+               // Texture dimensions and type are unchanged; it is more efficient
+               // to just update it rather than making an entirely new texture.
+               glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, width, height, format, type, data);
                check_error();
-               glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+       } else {
+               glTexImage2D(GL_TEXTURE_2D, 0, internal_format, width, height, 0, format, type, data);
                check_error();
+               last_texture_width = width;
+               last_texture_height = height;
+               last_texture_internal_format = internal_format;
+       }
+}
+
+void ResampleComputeEffect::get_compute_dimensions(unsigned output_width, unsigned output_height,
+                                                   unsigned *x, unsigned *y, unsigned *z) const
+{
+       *x = output_width;
+       *y = (output_height + uniform_output_samples_per_block - 1) / uniform_output_samples_per_block;
+       *z = 1;
+}
+
+void ResampleComputeEffect::set_gl_state(GLuint glsl_program_num, const string &prefix, unsigned *sampler_num)
+{
+       Effect::set_gl_state(glsl_program_num, prefix, sampler_num);
+
+       assert(input_width > 0);
+       assert(input_height > 0);
+       assert(output_width > 0);
+       assert(output_height > 0);
+
+       if (input_width != last_input_width ||
+           input_height != last_input_height ||
+           output_width != last_output_width ||
+           output_height != last_output_height ||
+           offset_x != last_offset_x ||
+           offset_y != last_offset_y ||
+           zoom_x != last_zoom_x ||
+           zoom_x != last_zoom_y) {
+               update_texture(glsl_program_num, prefix, sampler_num);
+               last_input_width = input_width;
+               last_input_height = input_height;
+               last_output_width = output_width;
+               last_output_height = output_height;
+               last_offset_x = offset_x;
+               last_offset_y = offset_y;
+               last_zoom_x = zoom_x;
+               last_zoom_y = zoom_y;
        }
+
+       glActiveTexture(GL_TEXTURE0 + *sampler_num);
+       check_error();
+       glBindTexture(GL_TEXTURE_2D, tex_horiz.get_texnum());
+       check_error();
+       uniform_sample_tex_horizontal = *sampler_num;
+       ++*sampler_num;
+
+       glActiveTexture(GL_TEXTURE0 + *sampler_num);
+       check_error();
+       glBindTexture(GL_TEXTURE_2D, tex_vert.get_texnum());
+       check_error();
+       uniform_sample_tex_vertical = *sampler_num;
+       ++*sampler_num;
+
+       uniform_num_horizontal_samples = src_horizontal_bilinear_samples;
+       uniform_num_vertical_samples = src_vertical_samples;
+       uniform_slice_height = slice_height;
+
+       uniform_horizontal_whole_pixel_offset = lrintf(offset_x) / float(input_width);
+       uniform_vertical_whole_pixel_offset = lrintf(offset_y);
+
+       uniform_inv_input_height = 1.0f / float(input_height);
+       uniform_input_texcoord_y_adjust = 0.5f / float(input_height);
 }
 
 }  // namespace movit