Implement wrapping of the resampling parameter texture.

[movit] / resample_effect.cpp

diff --git a/resample_effect.cpp b/resample_effect.cpp
index c0e82f1cb7c757088e2036b78a8d2ea1a34637c2..5b016861fafac36d0c55c4133323f1a6315b1846 100644 (file)
--- a/resample_effect.cpp
+++ b/resample_effect.cpp
@@ -29,6 +29,17 @@ float lanczos_weight(float x, float a)
        }
 }
 
+// Euclid's algorithm, from Wikipedia.
+unsigned gcd(unsigned a, unsigned b)
+{
+       while (b != 0) {
+               unsigned t = b;
+               b = a % b;
+               a = t;
+       }
+       return a;
+}
+
 }  // namespace
 
 ResampleEffect::ResampleEffect()
@@ -143,7 +154,6 @@ 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 of wrapping the sample texture.
 // 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)
 {
@@ -160,6 +170,16 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const std
                assert(false);
        }
 
+
+       // 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
+       // the first such loop, and then ask the card to repeat the texture for us.
+       // This is both easier on the texture cache and lowers our CPU cost for
+       // generating the kernel somewhat.
+       num_loops = gcd(src_size, dst_size);
+       slice_height = 1.0f / num_loops;
+       unsigned dst_samples = dst_size / num_loops;
+
        // Sample the kernel in the right place. A diagram with a triangular kernel
        // (corresponding to linear filtering, and obviously with radius 1)
        // for easier ASCII art drawing:
@@ -212,8 +232,8 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const std
        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;
-       float *weights = new float[dst_size * src_samples * 2];
-       for (unsigned y = 0; y < dst_size; ++y) {
+       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,
                // compensating for differing pixel centers as the scale changes.
                float center_src_y = (y + 0.5f) * float(src_size) / float(dst_size) - 0.5f;
@@ -228,8 +248,7 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const std
                }
        }
 
-       // Encode as a two-component texture. Note the GL_REPEAT, which is not relevant
-       // right now, but will be later.
+       // Encode as a two-component texture. Note the GL_REPEAT.
        glActiveTexture(GL_TEXTURE0 + *sampler_num);
        check_error();
        glBindTexture(GL_TEXTURE_2D, texnum);
@@ -240,11 +259,10 @@ 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_size, 0, GL_RG, GL_FLOAT, weights);
+       glTexImage2D(GL_TEXTURE_2D, 0, GL_RG16F, src_samples, dst_samples, 0, GL_RG, GL_FLOAT, weights);
        check_error();
 
        delete[] weights;
-
 }
 
 void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num)
@@ -270,6 +288,8 @@ 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_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);