Flesh out the blur code a little. It actually blurs now, although it is not as pretty...
authorSteinar H. Gunderson <sgunderson@bigfoot.com>
Wed, 3 Oct 2012 14:30:34 +0000 (16:30 +0200)
committerSteinar H. Gunderson <sgunderson@bigfoot.com>
Wed, 3 Oct 2012 14:30:34 +0000 (16:30 +0200)
blur_effect.cpp
blur_effect.frag

index 17044f1..fd81aa8 100644 (file)
@@ -8,6 +8,9 @@
 #include "blur_effect.h"
 #include "util.h"
 
+// Must match blur_effect.frag.
+#define NUM_TAPS 16
+
 BlurEffect::BlurEffect()
        : radius(3.0f),
          direction(HORIZONTAL)
@@ -25,16 +28,27 @@ void BlurEffect::set_uniforms(GLuint glsl_program_num, const std::string &prefix
 {
        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.
+       int base_texture_size, texture_size;
+       if (direction == HORIZONTAL) {
+               base_texture_size = texture_size = 1280;  // FIXME
+       } else if (direction == VERTICAL) {
+               base_texture_size = texture_size = 720;  // FIXME
+       } else {
+               assert(false);
+       }
+
+       // We only have 16 taps to work with on each side, 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.
+       //
+       // FIXME: we really need to pick the same mipmap level for both horizontal and vertical!
        unsigned base_mipmap_level = 0;
        float adjusted_radius = radius;
-       float pixel_size = 1.0f;
-       while (adjusted_radius * 2.5f > 7.0f) {
+       while (texture_size > 1 && adjusted_radius * 2.5f > NUM_TAPS / 2) {
                ++base_mipmap_level;
-               adjusted_radius *= 0.5f;
-               pixel_size *= 2.0f;
-       }       
+               texture_size /= 2;  // Rounding down.
+               adjusted_radius = radius * float(texture_size) / float(base_texture_size);
+       }
 
        // In the second pass, we do the same, but don't sample from a mipmap;
        // that would re-blur the other direction in an ugly fashion, and we already
@@ -47,32 +61,121 @@ void BlurEffect::set_uniforms(GLuint glsl_program_num, const std::string &prefix
        }
 
        glActiveTexture(GL_TEXTURE0);
+       check_error();
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, base_mipmap_level);
        check_error();
+       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, base_mipmap_level);
+       check_error();
 
-       // FIXME
-       if (direction == HORIZONTAL) {
-               float ps[] = { pixel_size / 1280.0f, 0.0f };
-               set_uniform_vec2(glsl_program_num, prefix, "pixel_offset", ps);
-       } else if (direction == VERTICAL) {
-               float ps[] = { 0.0f, pixel_size / 720.0f };
-               set_uniform_vec2(glsl_program_num, prefix, "pixel_offset", ps);
+       // Compute the weights; they will be symmetrical, so we only compute
+       // the right side.
+       float weight[NUM_TAPS + 1];
+       if (radius < 1e-3) {
+               weight[0] = 1.0f;
+               for (unsigned i = 1; i < NUM_TAPS + 1; ++i) {
+                       weight[i] = 0.0f;
+               }
        } else {
-               assert(false);
+               float sum = 0.0f;
+               for (unsigned i = 0; i < NUM_TAPS + 1; ++i) {
+                       float z = i / adjusted_radius;
+
+                       // 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.
+                       weight[i] = 1.0f / (cosh(z) * cosh(z));
+
+                       if (i == 0) {
+                               sum += weight[i];
+                       } else {
+                               sum += 2.0f * weight[i];
+                       }
+               }
+               for (unsigned i = 0; i < NUM_TAPS + 1; ++i) {
+                       weight[i] /= sum;
+               }
        }
 
-       // 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];
+#if 0
+       // NOTE: This is currently broken.
+
+       // 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.
+       float samples[4 * (NUM_TAPS / 2 + 1)];
+
+       // Center sample.
+       samples[4 * 0 + 0] = 0.0f;
+       samples[4 * 0 + 1] = 0.0f;
+       samples[4 * 0 + 2] = weight[0];
+       samples[4 * 0 + 3] = 0.0f;
+
+       // All other samples.
+       for (unsigned 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 offset, total_weight;
+               if (w1 + w2 < 1e-6) {
+                       offset = 0.5f;
+                       total_weight = 0.0f;
+               } else {
+                       offset = w2 / (w1 + w2);
+                       total_weight = w1 + w2;
+               }
+#if 0
+               // hack for easier visualization
+               offset = 0.5f;
+               total_weight = 8.0f;
+#endif
+               float x = 0.0f, y = 0.0f;
+
+               if (direction == HORIZONTAL) {
+                       x = (base_pos + offset) / (float)texture_size;
+               } else if (direction == VERTICAL) {
+                       y = (base_pos + offset) / (float)texture_size;
+               } else {
+                       assert(false);
+               }
+
+               samples[4 * i + 0] = x;
+               samples[4 * i + 1] = y;
+               samples[4 * i + 2] = total_weight;
+               samples[4 * i + 3] = 0.0f;
        }
-       printf("[mip level %d] ", base_mipmap_level);
-       for (unsigned i = 0; i < 15; ++i) {
-               weight[i] /= total;
-               printf("%f ", weight[i]);
+
+       set_uniform_vec4_array(glsl_program_num, prefix, "samples", samples, NUM_TAPS / 2 + 1);
+#else
+       // Boring, at-whole-pixels sampling.
+       float samples[4 * NUM_TAPS];
+
+       // All other samples.
+       for (unsigned i = 0; i < NUM_TAPS + 1; ++i) {
+               float x = 0.0f, y = 0.0f;
+
+               if (direction == HORIZONTAL) {
+                       x = i / (float)texture_size;
+               } else if (direction == VERTICAL) {
+                       y = i / (float)texture_size;
+               } else {
+                       assert(false);
+               }
+
+               samples[4 * i + 0] = x;
+               samples[4 * i + 1] = y;
+               samples[4 * i + 2] = weight[i];
+               samples[4 * i + 3] = 0.0f;
        }
-       printf("\n");
-       set_uniform_float_array(glsl_program_num, prefix, "weight", weight, 15);
+
+       set_uniform_vec4_array(glsl_program_num, prefix, "samples", samples, NUM_TAPS + 1);
+#endif
 }
index 8c0a01d..7e5a424 100644 (file)
@@ -1,24 +1,14 @@
 // A simple unidirectional blur.
 
-uniform vec2 PREFIX(pixel_offset);
-uniform float PREFIX(weight)[15];
+#define NUM_TAPS 16
+
+uniform vec4 PREFIX(samples)[NUM_TAPS + 1];
 
 vec4 FUNCNAME(vec2 tc) {
-       vec4 x = LAST_INPUT(tc);
-       return
-               vec4(PREFIX(weight)[ 0]) * LAST_INPUT(tc - 7.0 * PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[ 1]) * LAST_INPUT(tc - 6.0 * PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[ 2]) * LAST_INPUT(tc - 5.0 * PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[ 3]) * LAST_INPUT(tc - 4.0 * PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[ 4]) * LAST_INPUT(tc - 3.0 * PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[ 5]) * LAST_INPUT(tc - 2.0 * PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[ 6]) * LAST_INPUT(tc -       PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[ 7]) * LAST_INPUT(tc) +
-               vec4(PREFIX(weight)[ 8]) * LAST_INPUT(tc +       PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[ 9]) * LAST_INPUT(tc + 2.0 * PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[10]) * LAST_INPUT(tc + 3.0 * PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[11]) * LAST_INPUT(tc + 4.0 * PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[12]) * LAST_INPUT(tc + 5.0 * PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[13]) * LAST_INPUT(tc + 6.0 * PREFIX(pixel_offset)) +
-               vec4(PREFIX(weight)[14]) * LAST_INPUT(tc + 7.0 * PREFIX(pixel_offset));
+       vec4 sum = vec4(PREFIX(samples)[0].z) * LAST_INPUT(tc);
+       for (int i = 1; i < NUM_TAPS + 1; ++i) {
+               vec4 sample = PREFIX(samples)[i];
+               sum += vec4(sample.z) * (LAST_INPUT(tc - sample.xy) + LAST_INPUT(tc + sample.xy));
+       }
+       return sum;
 }