Fix a bug where the first black pass of SOR would read junk data.

[nageru] / sor.frag

diff --git a/sor.frag b/sor.frag
index ef431d3346d96be4e0270ddd6ad4c9ebd1664a63..b072839a2b3b86bc510f260bbb30ae3a93c5bb60 100644 (file)
--- a/sor.frag
+++ b/sor.frag
@@ -9,7 +9,7 @@ uniform sampler2D diff_flow_tex, diffusivity_tex;
 uniform usampler2D equation_red_tex, equation_black_tex;
 uniform int phase;
 
-uniform bool zero_diff_flow;
+uniform int num_nonzero_phases;
 
 // See pack_floats_shared() in equations.frag.
 vec2 unpack_floats_shared(uint c)
@@ -70,7 +70,7 @@ void main()
 
        const float omega = 1.8;  // Marginally better than 1.6, it seems.
 
-       if (zero_diff_flow) {
+       if (num_nonzero_phases == 0) {
                // Simplified version of the code below, assuming diff_flow == 0.0f everywhere.
                diff_flow.x = omega * b.x * inv_A11;
                diff_flow.y = omega * b.y * inv_A22;
@@ -87,7 +87,12 @@ void main()
                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;
-               diff_flow = texture(diff_flow_tex, tc).xy;
+
+               if (num_nonzero_phases == 1) {
+                       diff_flow = vec2(0.0f);
+               } else {
+                       diff_flow = texture(diff_flow_tex, tc).xy;
+               }
 
                // From https://en.wikipedia.org/wiki/Successive_over-relaxation.
                float sigma_u = A12 * diff_flow.y;