From: Steinar H. Gunderson Date: Sun, 28 Oct 2012 17:14:36 +0000 (+0100) Subject: Add the weight combining back, now that we have proper control over the interpolation... X-Git-Tag: 1.0~219 X-Git-Url: https://git.sesse.net/?p=movit;a=commitdiff_plain;h=17195eb5da34f03778cde297eb77c486fa0c51bc Add the weight combining back, now that we have proper control over the interpolation error. --- diff --git a/resample_effect.cpp b/resample_effect.cpp index 5b01686..c0afe0b 100644 --- a/resample_effect.cpp +++ b/resample_effect.cpp @@ -40,6 +40,58 @@ unsigned gcd(unsigned a, unsigned b) return a; } +unsigned combine_samples(float *src, float *dst, 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) { + // Copy the sample directly; it will be overwritten later if we can combine. + if (dst != NULL) { + dst[j * 2 + 0] = src[i * 2 + 0]; + dst[j * 2 + 1] = src[i * 2 + 1]; + } + + if (i == num_src_samples - 1) { + // Last sample; cannot combine. + continue; + } + assert(num_samples_saved <= max_samples_saved); + if (num_samples_saved == max_samples_saved) { + // We could maybe save more here, but other rows can't, so don't bother. + continue; + } + + float w1 = src[i * 2 + 0]; + float w2 = src[(i + 1) * 2 + 0]; + if (w1 * w2 < 0.0f) { + // Differing signs; cannot combine. + continue; + } + + float pos1 = src[i * 2 + 1]; + float pos2 = src[(i + 1) * 2 + 1]; + assert(pos2 > pos1); + + float offset, total_weight, sum_sq_error; + combine_two_samples(w1, w2, &offset, &total_weight, &sum_sq_error); + + // If the interpolation error is larger than that of one level + // at 8-bit precision, don't combine. + if (sum_sq_error > 1.0f / (256.0f * 256.0f)) { + continue; + } + + // OK, we can combine this and the next sample. + if (dst != NULL) { + dst[j * 2 + 0] = total_weight; + dst[j * 2 + 1] = pos1 + offset * (pos2 - pos1); + } + + ++i; // Skip the next sample. + ++num_samples_saved; + } + return num_samples_saved; +} + } // namespace ResampleEffect::ResampleEffect() @@ -153,8 +205,6 @@ std::string SingleResamplePassEffect::output_fragment_shader() // // For horizontal scaling, we fill in the exact same texture; // the shader just interprets is differently. -// -// TODO: Support optimization using free linear sampling, like in BlurEffect. void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num) { unsigned src_size, dst_size; @@ -231,7 +281,7 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const std // Thus, the kernel width will vary with how much we scale. float radius_scaling_factor = std::min(float(dst_size) / float(src_size), 1.0f); int int_radius = lrintf(LANCZOS_RADIUS / radius_scaling_factor); - src_samples = int_radius * 2 + 1; + int src_samples = int_radius * 2 + 1; float *weights = new float[dst_samples * src_samples * 2]; for (unsigned y = 0; y < dst_samples; ++y) { // Find the point around which we want to sample the source image, @@ -248,6 +298,31 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const std } } + // 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; + for (unsigned y = 0; y < dst_samples; ++y) { + unsigned num_samples_saved = combine_samples(weights + (y * src_samples) * 2, NULL, src_samples, UINT_MAX); + src_bilinear_samples = std::max(src_bilinear_samples, src_samples - num_samples_saved); + } + + // Now that we know the right width, actually combine the samples. + float *bilinear_weights = new float[dst_samples * src_bilinear_samples * 2]; + for (unsigned y = 0; y < dst_samples; ++y) { + unsigned num_samples_saved = combine_samples( + weights + (y * src_samples) * 2, + bilinear_weights + (y * src_bilinear_samples) * 2, + src_samples, + src_samples - src_bilinear_samples); + assert(int(src_samples) - int(num_samples_saved) == src_bilinear_samples); + } + // Encode as a two-component texture. Note the GL_REPEAT. glActiveTexture(GL_TEXTURE0 + *sampler_num); check_error(); @@ -259,10 +334,11 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const std check_error(); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT); check_error(); - glTexImage2D(GL_TEXTURE_2D, 0, GL_RG16F, src_samples, dst_samples, 0, GL_RG, GL_FLOAT, weights); + glTexImage2D(GL_TEXTURE_2D, 0, GL_RG16F, src_bilinear_samples, dst_samples, 0, GL_RG, GL_FLOAT, bilinear_weights); check_error(); delete[] weights; + delete[] bilinear_weights; } void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num) @@ -287,13 +363,13 @@ void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const std:: set_uniform_int(glsl_program_num, prefix, "sample_tex", *sampler_num); ++sampler_num; - set_uniform_int(glsl_program_num, prefix, "num_samples", src_samples); + set_uniform_int(glsl_program_num, prefix, "num_samples", src_bilinear_samples); set_uniform_float(glsl_program_num, prefix, "num_loops", num_loops); set_uniform_float(glsl_program_num, prefix, "slice_height", slice_height); // Instructions for how to convert integer sample numbers to positions in the weight texture. - set_uniform_float(glsl_program_num, prefix, "sample_x_scale", 1.0f / src_samples); - set_uniform_float(glsl_program_num, prefix, "sample_x_offset", 0.5f / src_samples); + set_uniform_float(glsl_program_num, prefix, "sample_x_scale", 1.0f / src_bilinear_samples); + set_uniform_float(glsl_program_num, prefix, "sample_x_offset", 0.5f / src_bilinear_samples); // We specifically do not want mipmaps on the input texture; // they break minification. diff --git a/resample_effect.h b/resample_effect.h index 1424bbf..5867f25 100644 --- a/resample_effect.h +++ b/resample_effect.h @@ -87,7 +87,7 @@ private: GLuint texnum; int input_width, input_height, output_width, output_height; int last_input_width, last_input_height, last_output_width, last_output_height; - int src_samples, num_loops; + int src_bilinear_samples, num_loops; float slice_height; };