Finally get SOR working.

[nageru] / sor.frag

diff --git a/sor.frag b/sor.frag
index f6ac2ee5adaf0780c67eb23783de58b45e17b222..fbcc2e4ca8b8532b829a7c653b88757310448fba 100644 (file)
--- a/sor.frag
+++ b/sor.frag
@@ -1,34 +1,63 @@
 #version 450 core
 
 in vec2 tc;
+in float element_sum_idx;
 out vec2 diff_flow;
 
 uniform sampler2D diff_flow_tex, smoothness_x_tex, smoothness_y_tex;
 uniform usampler2D equation_tex;
+uniform vec2 image_size;
+uniform int phase;
+
+// See pack_floats_shared() in equations.frag.
+vec2 unpack_floats_shared(uint c)
+{
+       // Recover the exponent, and multiply it in. Add one because
+       // we have denormalized mantissas, then another one because we
+       // already reduced the exponent by one. Then subtract 20, because
+       // we are going to shift up the number by 20 below to recover the sign bits.
+       float normalizer = uintBitsToFloat(((c >> 1) & 0x7f800000u) - (18 << 23));
+       normalizer *= (1.0 / 2047.0);
+
+       // Shift the values up so that we recover the sign bit, then normalize.
+       float a = int(uint(c & 0x000fffu) << 20) * normalizer;
+       float b = int(uint(c & 0xfff000u) << 8) * normalizer;
+
+       return vec2(a, b);
+}
 
 void main()
 {
+       // Red-black SOR: Every other pass, we update every other element in a
+       // checkerboard pattern. This is rather suboptimal for the GPU, as it
+       // just immediately throws away half of the warp, but it helps convergence
+       // a _lot_ (rough testing indicates that five iterations of SOR is as good
+       // as ~50 iterations of Jacobi). We could probably do better by reorganizing
+       // the data into two-values-per-pixel, so-called “twinning buffering”,
+       // but it makes for rather annoying code in the rest of the pipeline.
+       int color = int(round(element_sum_idx)) & 1;
+       if (color != phase) discard;
+
        uvec4 equation = texture(equation_tex, tc);
        float inv_A11 = uintBitsToFloat(equation.x);
        float A12 = uintBitsToFloat(equation.y);
        float inv_A22 = uintBitsToFloat(equation.z);
-       vec2 b = unpackHalf2x16(equation.w);
+       vec2 b = unpack_floats_shared(equation.w);
 
        // Subtract the missing terms from the right-hand side
        // (it couldn't be done earlier, because we didn't know
        // the values of the neighboring pixels; they change for
        // each SOR iteration).
-       // TODO: Multiply by some gamma.
        float smooth_l = textureOffset(smoothness_x_tex, tc, ivec2(-1,  0)).x;
        float smooth_r = texture(smoothness_x_tex, tc).x;
        float smooth_d = textureOffset(smoothness_y_tex, tc, ivec2( 0, -1)).x;
        float smooth_u = texture(smoothness_y_tex, tc).x;
-       b -= smooth_l * textureOffset(diff_flow_tex, tc, ivec2(-1,  0)).xy;
-       b -= smooth_r * textureOffset(diff_flow_tex, tc, ivec2( 1,  0)).xy;
-       b -= smooth_d * textureOffset(diff_flow_tex, tc, ivec2( 0, -1)).xy;
-       b -= smooth_u * textureOffset(diff_flow_tex, tc, ivec2( 0,  1)).xy;
+       b += smooth_l * textureOffset(diff_flow_tex, tc, ivec2(-1,  0)).xy;
+       b += smooth_r * textureOffset(diff_flow_tex, tc, ivec2( 1,  0)).xy;
+       b += smooth_d * textureOffset(diff_flow_tex, tc, ivec2( 0, -1)).xy;
+       b += smooth_u * textureOffset(diff_flow_tex, tc, ivec2( 0,  1)).xy;
 
-       const float omega = 1.6;
+       const float omega = 1.8;  // Marginally better than 1.6, it seems.
        diff_flow = texture(diff_flow_tex, tc).xy;
 
        // From https://en.wikipedia.org/wiki/Successive_over-relaxation.