From c62391987241f1482a99b6f6417fbec1d0ef2344 Mon Sep 17 00:00:00 2001 From: "Steinar H. Gunderson" Date: Sat, 21 Feb 2015 18:54:56 +0100 Subject: [PATCH] Make ResampleEffect fall back to fp32 as needed. This should kill all precision issues when zooming. There are still a few tricks we can do to improve fp16, but that's primarily a performance issue. --- resample_effect.cpp | 167 ++++++++++++++++++++++++++++++--------- resample_effect_test.cpp | 2 +- 2 files changed, 130 insertions(+), 39 deletions(-) diff --git a/resample_effect.cpp b/resample_effect.cpp index 9838cd4..f4808c4 100644 --- a/resample_effect.cpp +++ b/resample_effect.cpp @@ -11,6 +11,7 @@ #include "effect_chain.h" #include "effect_util.h" #include "fp16.h" +#include "init.h" #include "resample_effect.h" #include "util.h" @@ -56,7 +57,7 @@ unsigned gcd(unsigned a, unsigned b) } template -unsigned combine_samples(Tap *src, Tap *dst, unsigned src_size, unsigned num_src_samples, unsigned max_samples_saved) +unsigned combine_samples(const Tap *src, Tap *dst, unsigned src_size, unsigned num_src_samples, unsigned max_samples_saved) { unsigned num_samples_saved = 0; for (unsigned i = 0, j = 0; i < num_src_samples; ++i, ++j) { @@ -96,7 +97,7 @@ unsigned combine_samples(Tap *src, Tap *dst, unsigned src_size // but since the artifacts are not really random, they can get quite // visible. On the other hand, going to 0.25f, I can see no change at // all with 8-bit output, so it would not seem to be worth it.) - if (sum_sq_error > 0.5f / (256.0f * 256.0f)) { + if (sum_sq_error > 0.5f / (255.0f * 255.0f)) { continue; } @@ -112,6 +113,109 @@ unsigned combine_samples(Tap *src, Tap *dst, unsigned src_size return num_samples_saved; } +// 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 +// figure out the maximum number of samples. Then, we downconvert all the weights to +// that number -- we could have gone for a variable-length system, but this is simpler, +// and the gains would probably be offset by the extra cost of checking when to stop. +// +// The greedy strategy for combining samples is optimal. +template +unsigned combine_many_samples(const Tap *weights, unsigned src_size, unsigned src_samples, unsigned dst_samples, Tap **bilinear_weights) +{ + int src_bilinear_samples = 0; + for (unsigned y = 0; y < dst_samples; ++y) { + unsigned num_samples_saved = combine_samples(weights + y * src_samples, NULL, src_size, src_samples, UINT_MAX); + src_bilinear_samples = max(src_bilinear_samples, src_samples - num_samples_saved); + } + + // Now that we know the right width, actually combine the samples. + *bilinear_weights = new Tap[dst_samples * src_bilinear_samples]; + for (unsigned y = 0; y < dst_samples; ++y) { + Tap *bilinear_weights_ptr = *bilinear_weights + y * src_bilinear_samples; + unsigned num_samples_saved = combine_samples( + weights + y * src_samples, + bilinear_weights_ptr, + src_size, + src_samples, + src_samples - src_bilinear_samples); + assert(int(src_samples) - int(num_samples_saved) == src_bilinear_samples); + + // Normalize so that the sum becomes one. Note that we do it twice; + // this sometimes helps a tiny little bit when we have many samples. + for (int normalize_pass = 0; normalize_pass < 2; ++normalize_pass) { + double sum = 0.0; + for (int i = 0; i < src_bilinear_samples; ++i) { + sum += to_fp64(bilinear_weights_ptr[i].weight); + } + for (int i = 0; i < src_bilinear_samples; ++i) { + bilinear_weights_ptr[i].weight = from_fp64( + to_fp64(bilinear_weights_ptr[i].weight) / sum); + } + } + } + return src_bilinear_samples; +} + +// Compute the sum of squared errors between the ideal weights (which are +// assumed to fall exactly on pixel centers) and the weights that result +// from sampling at . The primary reason for the difference +// is inaccuracy in the sampling positions, both due to limited precision +// in storing them (already inherent in sending them in as fp16_int_t) +// and in subtexel sampling precision (which we calculate in this function). +template +double compute_sum_sq_error(const Tap* weights, unsigned num_weights, + const Tap* bilinear_weights, unsigned num_bilinear_weights, + unsigned size) +{ + // 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_fp64(bilinear_weights[0].pos) * size - 0.5)); + int upper_pos = int(ceil(to_fp64(bilinear_weights[num_bilinear_weights - 1].pos) * size - 0.5)) + 2; + lower_pos = min(lower_pos, lrintf(weights[0].pos * size - 0.5)); + upper_pos = max(upper_pos, lrintf(weights[num_weights - 1].pos * size - 0.5)); + + float* effective_weights = new float[upper_pos - lower_pos]; + for (int i = 0; i < upper_pos - lower_pos; ++i) { + effective_weights[i] = 0.0f; + } + + // Now find the effective weights that result from this sampling. + for (unsigned i = 0; i < num_bilinear_weights; ++i) { + const float pixel_pos = to_fp64(bilinear_weights[i].pos) * size - 0.5f; + const int x0 = int(floor(pixel_pos)) - lower_pos; + const int x1 = x0 + 1; + const float f = lrintf((pixel_pos - (x0 + lower_pos)) / movit_texel_subpixel_precision) * movit_texel_subpixel_precision; + + assert(x0 >= 0); + assert(x1 >= 0); + assert(x0 < upper_pos - lower_pos); + assert(x1 < upper_pos - lower_pos); + + effective_weights[x0] += to_fp64(bilinear_weights[i].weight) * (1.0 - f); + effective_weights[x1] += to_fp64(bilinear_weights[i].weight) * f; + } + + // Subtract the desired weights to get the error. + for (unsigned i = 0; i < num_weights; ++i) { + const int x = lrintf(weights[i].pos * size - 0.5f) - lower_pos; + assert(x >= 0); + assert(x < upper_pos - lower_pos); + + effective_weights[x] -= weights[i].weight; + } + + double sum_sq_error = 0.0; + for (unsigned i = 0; i < num_weights; ++i) { + sum_sq_error += effective_weights[i] * effective_weights[i]; + } + + delete[] effective_weights; + return sum_sq_error; +} + } // namespace ResampleEffect::ResampleEffect() @@ -397,43 +501,25 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const str } // Now 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 - // figure out the maximum number of samples. Then, we downconvert all the weights to - // that number -- we could have gone for a variable-length system, but this is simpler, - // and the gains would probably be offset by the extra cost of checking when to stop. - // - // The greedy strategy for combining samples is optimal. - src_bilinear_samples = 0; + // we need to make. Try fp16 first; if it's not accurate enough, we go to fp32. + Tap *bilinear_weights_fp16; + src_bilinear_samples = combine_many_samples(weights, src_size, src_samples, dst_samples, &bilinear_weights_fp16); + Tap *bilinear_weights_fp32 = NULL; + bool fallback_to_fp32 = false; + double max_sum_sq_error_fp16 = 0.0; for (unsigned y = 0; y < dst_samples; ++y) { - unsigned num_samples_saved = combine_samples(weights + y * src_samples, NULL, src_size, src_samples, UINT_MAX); - src_bilinear_samples = max(src_bilinear_samples, src_samples - num_samples_saved); + double sum_sq_error_fp16 = compute_sum_sq_error( + weights + y * src_samples, src_samples, + bilinear_weights_fp16 + 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); } - // Now that we know the right width, actually combine the samples. - Tap *bilinear_weights = new Tap[dst_samples * src_bilinear_samples]; - for (unsigned y = 0; y < dst_samples; ++y) { - Tap *bilinear_weights_ptr = bilinear_weights + y * src_bilinear_samples; - unsigned num_samples_saved = combine_samples( - weights + y * src_samples, - bilinear_weights_ptr, - src_size, - src_samples, - src_samples - src_bilinear_samples); - assert(int(src_samples) - int(num_samples_saved) == src_bilinear_samples); - - // Normalize so that the sum becomes one. Note that we do it twice; - // this sometimes helps a tiny little bit when we have many samples. - for (int normalize_pass = 0; normalize_pass < 2; ++normalize_pass) { - double sum = 0.0; - for (int i = 0; i < src_bilinear_samples; ++i) { - sum += fp16_to_fp64(bilinear_weights_ptr[i].weight); - } - for (int i = 0; i < src_bilinear_samples; ++i) { - bilinear_weights_ptr[i].weight = fp64_to_fp16( - fp16_to_fp64(bilinear_weights_ptr[i].weight) / sum); - } - } + // 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. + if (max_sum_sq_error_fp16 > 2.0f / (255.0f * 255.0f)) { + fallback_to_fp32 = true; + src_bilinear_samples = combine_many_samples(weights, src_size, src_samples, dst_samples, &bilinear_weights_fp32); } // Encode as a two-component texture. Note the GL_REPEAT. @@ -447,11 +533,16 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const str check_error(); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT); check_error(); - glTexImage2D(GL_TEXTURE_2D, 0, GL_RG16F, src_bilinear_samples, dst_samples, 0, GL_RG, GL_HALF_FLOAT, bilinear_weights); + if (fallback_to_fp32) { + glTexImage2D(GL_TEXTURE_2D, 0, GL_RG32F, src_bilinear_samples, dst_samples, 0, GL_RG, GL_FLOAT, bilinear_weights_fp32); + } else { + glTexImage2D(GL_TEXTURE_2D, 0, GL_RG16F, src_bilinear_samples, dst_samples, 0, GL_RG, GL_HALF_FLOAT, bilinear_weights_fp16); + } check_error(); delete[] weights; - delete[] bilinear_weights; + delete[] bilinear_weights_fp16; + delete[] bilinear_weights_fp32; } void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const string &prefix, unsigned *sampler_num) diff --git a/resample_effect_test.cpp b/resample_effect_test.cpp index 5b620fd..353429e 100644 --- a/resample_effect_test.cpp +++ b/resample_effect_test.cpp @@ -402,7 +402,7 @@ TEST(ResampleEffectTest, VerticalZoomFromTop) { } TEST(ResampleEffectTest, Precision) { - const int size = 2048; + const int size = 1920; // Difficult non-power-of-two size. const int offset = 5; // Deliberately put the data of interest very close to the right, -- 2.39.2