+
+SingleBlurPassEffect::~SingleBlurPassEffect()
+{
+ delete[] uniform_samples;
+}
+
+string SingleBlurPassEffect::output_fragment_shader()
+{
+ char buf[256];
+ sprintf(buf, "#define DIRECTION_VERTICAL %d\n#define NUM_TAPS %d\n",
+ (direction == VERTICAL), num_taps);
+ uniform_samples = new float[2 * (num_taps / 2 + 1)];
+ register_uniform_vec2_array("samples", uniform_samples, num_taps / 2 + 1);
+ return buf + read_file("blur_effect.frag");
+}
+
+void SingleBlurPassEffect::set_gl_state(GLuint glsl_program_num, const string &prefix, unsigned *sampler_num)
+{
+ Effect::set_gl_state(glsl_program_num, prefix, sampler_num);
+
+ // Compute the weights; they will be symmetrical, so we only compute
+ // the right side.
+ float* weight = new float[num_taps + 1];
+ if (radius < 1e-3) {
+ weight[0] = 1.0f;
+ for (int i = 1; i < num_taps + 1; ++i) {
+ weight[i] = 0.0f;
+ }
+ } else {
+ float sum = 0.0f;
+ for (int i = 0; i < num_taps + 1; ++i) {
+ // Gaussian blur is a common, but maybe not the prettiest choice;
+ // it can feel a bit too blurry in the fine detail and too little
+ // long-tail. This is a simple logistic distribution, which has
+ // a narrower peak but longer tails.
+ //
+ // We interpret the radius as sigma, similar to Gaussian blur.
+ // Wikipedia says that sigma² = pi² s² / 3, which yields:
+ const float s = (sqrt(3.0) / M_PI) * radius;
+ float z = i / (2.0 * s);
+
+ weight[i] = 1.0f / (cosh(z) * cosh(z));
+
+ if (i == 0) {
+ sum += weight[i];
+ } else {
+ sum += 2.0f * weight[i];
+ }
+ }
+ for (int i = 0; i < num_taps + 1; ++i) {
+ weight[i] /= sum;
+ }
+ }
+
+ // Since the GPU gives us bilinear sampling for free, we can get two
+ // samples for the price of one (for every but the center sample,
+ // in which case this trick doesn't buy us anything). Simply sample
+ // between the two pixel centers, and we can do with fewer weights.
+ // (This is right even in the vertical pass where we don't actually
+ // sample between the pixels, because we have linear interpolation
+ // there too.)
+ //
+ // We pack the parameters into a float4: The relative sample coordinates
+ // in (x,y), and the weight in z. w is unused.
+
+ // Center sample.
+ uniform_samples[2 * 0 + 0] = 0.0f;
+ uniform_samples[2 * 0 + 1] = weight[0];
+
+ int size;
+ if (direction == HORIZONTAL) {
+ size = width;
+ } else if (direction == VERTICAL) {
+ size = height;
+ } else {
+ assert(false);
+ }
+ float num_subtexels = size / movit_texel_subpixel_precision;
+ float inv_num_subtexels = movit_texel_subpixel_precision / size;
+
+ // All other samples.
+ for (int i = 1; i < num_taps / 2 + 1; ++i) {
+ unsigned base_pos = i * 2 - 1;
+ float w1 = weight[base_pos];
+ float w2 = weight[base_pos + 1];
+
+ float pos1 = base_pos / (float)size;
+ float pos2 = (base_pos + 1) / (float)size;
+ float pos, total_weight;
+ combine_two_samples(w1, w2, pos1, pos2, num_subtexels, inv_num_subtexels, &pos, &total_weight, NULL);
+
+ uniform_samples[2 * i + 0] = pos;
+ uniform_samples[2 * i + 1] = total_weight;
+ }
+
+ delete[] weight;
+}
+
+void SingleBlurPassEffect::clear_gl_state()
+{
+}
+
+} // namespace movit