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 ddf542eec62fea98c362ba726d3b942bb0b61fa7..7ca895a15f6b56b8dfee4e53a0f013610097d0de 100644 (file)
--- a/blur_effect.cpp
+++ b/blur_effect.cpp
@@ -22,22 +22,34 @@ void BlurEffect::set_uniforms(GLuint glsl_program_num, const std::string &prefix
 {
        Effect::set_uniforms(glsl_program_num, prefix, sampler_num);
 
-       //glActiveTexture(GL_TEXTURE0);
-       //glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 3);
-       //check_error();
-
-       set_uniform_float(glsl_program_num, prefix, "pixel_offset", 1.0f / 1280.0f);  // FIXME
+       // 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) / radius;
+               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\n", weight[i]);
+               printf("%f ", weight[i]);
        }
        printf("\n");
        set_uniform_float_array(glsl_program_num, prefix, "weight", weight, 15);