[#106] Add motion blur mirrored background reconstruction from Jimenez paper

projects/indirect_dispatch/resources/shaders/motionBlur.comp

@@ -175,21 +175,50 @@ void main(){
     // the sampleUV code expects an offset in range [-0.5, 0.5], so the dither is rescaled to a binary -0.25/0.25
     float random = dither(coord) * 0.5 - 0.25;
     
-    const int sampleCount = 15; 
+    const int sampleCountHalf = 8; 
     
-    for(int i = 0; i < sampleCount; i++){
-        vec2 sampleUV = mix(uvStart, uvEnd, (i + random + 1) / float(sampleCount + 1));
+    // two samples are processed at a time to allow for mirrored background reconstruction
+    for(int i = 0; i < sampleCountHalf; i++){
         
-        SampleData  samplePixel     = loadSampleData(sampleUV);
-        float       weightSample    = computeSampleWeigth(mainPixel, samplePixel);
+        vec2 sampleUV1 = mix(uv, uvEnd,     (i + random + 1) / float(sampleCountHalf + 1));
+        vec2 sampleUV2 = mix(uv, uvStart,   (i + random + 1) / float(sampleCountHalf + 1));
         
-        weightSum   += weightSample;
-        color       += samplePixel.color * weightSample;
+        SampleData sample1 = loadSampleData(sampleUV1);
+        SampleData sample2 = loadSampleData(sampleUV2);
+        
+        float weight1 = computeSampleWeigth(mainPixel, sample1);
+        float weight2 = computeSampleWeigth(mainPixel, sample2);
+
+        bool mirroredBackgroundReconstruction = true;
+        if(mirroredBackgroundReconstruction){
+            // see Jimenez paper for details and comparison
+            // problem is that in the foreground the background is reconstructed, which is blurry
+            // in the background the background is obviously known, so it is sharper
+            // at the border between fore- and background this causes a discontinuity
+            // to fix this the weights are mirrored on this border, effectively reconstructing the background, even though it is known
+            
+            // these bools check if sample1 is an affected background pixel (further away and slower moving than sample2)
+            bool inBackground = sample1.depthLinear     > sample2.depthLinear;
+            bool blurredOver  = sample1.velocityPixels  < sample2.velocityPixels;
+            
+            // this mirrors the weights depending on the results:
+            // if both conditions are true,   then weight2 is mirrored to weight1
+            // if both conditions are false,  then weight1 is mirrored to weight2, as sample2 is an affected background pixel
+            // if only one condition is true, then the weights are kept as is
+            weight1 = inBackground && blurredOver ? weight2 : weight1;
+            weight2 = inBackground || blurredOver ? weight2 : weight1;
+        }
+        
+        weightSum   += weight1;
+        weightSum   += weight2;
+        
+        color       += sample1.color * weight1;
+        color       += sample2.color * weight2;
     }
     
     // normalize color and weight
-    weightSum   /= sampleCount;
-    color       /= sampleCount;
+    weightSum   /= sampleCountHalf * 2;
+    color       /= sampleCountHalf * 2;
     
     // the main color is considered the background
     // the weight sum can be interpreted as the alpha of the combined samples, see Jimenez paper