Even out the fog cells with their neighbours and stagger the points next to lamps

shaders/fog_integrate.comp

@@ -1,7 +1,9 @@
 // the fog volume of the main view, second pass: the light and extinction of the cells (fog_inject.comp) added up along the rays
 // of the view, front to back, into what the fog adds and lets through from the camera to the far side of every slice
 // (apply_fog.glsl). the light of a cell is integrated over its length as Hillaire (2015) does it, so it doesn't grow with
-// the size of the cell
+// the size of the cell. the light of the cells is taken with the light of their neighbours across the view, a 3x3 tent filter
+// (four fetches of the linear filter): every cell is sampled at a point of its own in a frame, and what is left of that after
+// the blending over frames differs from cell to cell, which the filter evens out. the history keeps the cells unfiltered
 
 #include <common>
 
@@ -35,6 +37,12 @@ void main()
 		float span = (back - front) * stretch;
 		front = back;
 		vec4 cell = texelFetch(fog_scattering, ivec3(column, slice), 0);
+		float depthcoord = (float(slice) + 0.5) / float(grid.z);
+		vec2 texel = 1.0 / vec2(grid.xy);
+		cell.rgb = 0.25 * (textureLod(fog_scattering, vec3(coords + vec2(-0.5, -0.5) * texel, depthcoord), 0.0).rgb
+		                 + textureLod(fog_scattering, vec3(coords + vec2(0.5, -0.5) * texel, depthcoord), 0.0).rgb
+		                 + textureLod(fog_scattering, vec3(coords + vec2(-0.5, 0.5) * texel, depthcoord), 0.0).rgb
+		                 + textureLod(fog_scattering, vec3(coords + vec2(0.5, 0.5) * texel, depthcoord), 0.0).rgb);
 		float extinction = max(cell.a, 1e-7);
 		float through = exp(-extinction * span);
 		light += transmittance * cell.rgb * ((1.0 - through) / extinction);