Realtime Compositor: Implement blur node

This patch implements the blur node for the realtime compositor. The patch is
still missing the Variable Size option because it depends on the Erode/Dilate
node, which is yet to be implemented. Furthermore, there are a number of
optimizations that can be implemented, the most important of which is the IIR
implementation of the Fast Gaussian filter, as well as the use of hardware
filtering and thread local memory. The latter of which was attempted but was
not robust enough, so it will be submitted as separate patch.

Differential Revision: https://developer.blender.org/D15663

Reviewed By: Clement Foucault

1 files changed, 32 insertions, 0 deletions

diff --git a/source/blender/gpu/shaders/compositor/library/gpu_shader_compositor_blur_common.glsl b/source/blender/gpu/shaders/compositor/library/gpu_shader_compositor_blur_common.glsl
new file mode 100644
index 00000000000..e404c03bbb0
--- /dev/null
+++ b/source/blender/gpu/shaders/compositor/library/gpu_shader_compositor_blur_common.glsl
@@ -0,0 +1,32 @@
+/* Preprocess the input of the blur filter by squaring it in its alpha straight form, assuming the
+ * given color is alpha premultiplied. */
+vec4 gamma_correct_blur_input(vec4 color)
+{
+  /* Unpremultiply alpha. */
+  color.rgb /= color.a > 0.0 ? color.a : 1.0;
+
+  /* Square color channel if it is positive, otherwise zero it. */
+  color.rgb *= mix(color.rgb, vec3(0.0), lessThan(color.rgb, vec3(0.0)));
+
+  /* Premultiply alpha to undo previous alpha unpremultiplication. */
+  color.rgb *= color.a > 0.0 ? color.a : 1.0;
+
+  return color;
+}
+
+/* Postprocess the output of the blur filter by taking its square root it in its alpha straight
+ * form, assuming the given color is alpha premultiplied. This essential undoes the processing done
+ * by the gamma_correct_blur_input function. */
+vec4 gamma_uncorrect_blur_output(vec4 color)
+{
+  /* Unpremultiply alpha. */
+  color.rgb /= color.a > 0.0 ? color.a : 1.0;
+
+  /* Take the square root of the color channel if it is positive, otherwise zero it. */
+  color.rgb = mix(sqrt(color.rgb), vec3(0.0), lessThan(color.rgb, vec3(0.0)));
+
+  /* Premultiply alpha to undo previous alpha unpremultiplication. */
+  color.rgb *= color.a > 0.0 ? color.a : 1.0;
+
+  return color;
+}