Try to adjust the mip levels to get box blur for free as needed.

[movit] / blur_effect.cpp

diff --git a/blur_effect.cpp b/blur_effect.cpp
index e945295da641dd565c74b54684be93e158de0022..7ca895a15f6b56b8dfee4e53a0f013610097d0de 100644 (file)
--- a/blur_effect.cpp
+++ b/blur_effect.cpp
@@ -8,7 +8,7 @@
 #include "util.h"
 
 BlurEffect::BlurEffect()
-       : radius(0.3f)
+       : radius(3.0f)
 {
        register_float("radius", (float *)&radius);
 }
@@ -21,4 +21,36 @@ std::string BlurEffect::output_fragment_shader()
 void BlurEffect::set_uniforms(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num)
 {
        Effect::set_uniforms(glsl_program_num, prefix, sampler_num);
+
+       // We only have 15 taps to work with, and we want that to reach out to about 2.5*sigma.
+       // Bump up the mipmap levels (giving us box blurs) until we have what we need.
+       unsigned base_mipmap_level = 0;
+       float adjusted_radius = radius;
+       float pixel_size = 1.0f;
+       while (adjusted_radius * 2.5f > 7.0f) {
+               ++base_mipmap_level;
+               adjusted_radius *= 0.5f;
+               pixel_size *= 2.0f;
+       }       
+
+       glActiveTexture(GL_TEXTURE0);
+       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, base_mipmap_level);
+       check_error();
+
+       set_uniform_float(glsl_program_num, prefix, "pixel_offset", pixel_size / 1280.0f);  // FIXME
+
+       // Simple Gaussian weights for now.
+       float weight[15], total = 0.0f;
+       for (unsigned i = 0; i < 15; ++i) {
+               float z = (i - 7.0f) / adjusted_radius;
+               weight[i] = exp(-(z*z));
+               total += weight[i];
+       }
+       printf("[mip level %d] ", base_mipmap_level);
+       for (unsigned i = 0; i < 15; ++i) {
+               weight[i] /= total;
+               printf("%f ", weight[i]);
+       }
+       printf("\n");
+       set_uniform_float_array(glsl_program_num, prefix, "weight", weight, 15);
 }