Checkerboard fixes and prep

This code was written on stream but was not committed; this will allow
easier experimentation with actual temporal reprojection.

src/niagara.cpp

@@ -1478,6 +1478,7 @@ int main(int argc, const char** argv)
 
 			// checkerboard rendering: we dispatch half as many columns and xform them to fill the screen
 			int shadowWidthCB = shadowCheckerboard ? (swapchain.width + 1) / 2 : swapchain.width;
+			int shadowCheckerboardF = shadowCheckerboard ? 1 + (frameIndex % 2) : 0;
 
 			vkCmdWriteTimestamp(commandBuffer, VK_PIPELINE_STAGE_ALL_COMMANDS_BIT, queryPoolTimestamp, timestamp + 0);
 
@@ -1500,7 +1501,7 @@ int main(int argc, const char** argv)
 				shadowData.sunJitter = shadowblurEnabled ? 1e-2f : 0;
 				shadowData.inverseViewProjection = inverse(projection * view);
 				shadowData.imageSize = vec2(float(swapchain.width), float(swapchain.height));
-				shadowData.checkerboard = shadowCheckerboard;
+				shadowData.checkerboard = shadowCheckerboardF;
 
 				dispatch(commandBuffer, shadowProgram, shadowWidthCB, swapchain.height, shadowData, descriptors);
 			}
@@ -1520,8 +1521,9 @@ int main(int argc, const char** argv)
 				DescriptorInfo descriptors[] = { { shadowTarget.imageView, VK_IMAGE_LAYOUT_GENERAL }, { readSampler, depthTarget.imageView, VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL } };
 
 				vec4 fillData = vec4(float(swapchain.width), float(swapchain.height), 0, 0);
+				memcpy(&fillData.z, &shadowCheckerboardF, sizeof(shadowCheckerboardF));
 
-				dispatch(commandBuffer, shadowProgram, shadowWidthCB, swapchain.height, fillData, descriptors);
+				dispatch(commandBuffer, shadowfillProgram, shadowWidthCB, swapchain.height, fillData, descriptors);
 			}
 
 			for (int pass = 0; pass < (shadowblurEnabled ? 2 : 0); ++pass)

src/shaders/shadow.comp.glsl

@@ -22,7 +22,7 @@ struct ShadowData
 	mat4 inverseViewProjection;
 
 	vec2 imageSize;
-	uint checkerboard;
+	int checkerboard;
 };
 
 layout(push_constant) uniform block
@@ -115,11 +115,11 @@ bool shadowTraceTransparent(vec3 wpos, vec3 dir, uint rayflags)
 
 void main()
 {
-	uvec2 pos = gl_GlobalInvocationID.xy;
+	ivec2 pos = ivec2(gl_GlobalInvocationID.xy);
 
 	if (shadowData.checkerboard > 0)
 	{
-		// checkerboard even
+		// checkerboard
 		pos.x *= 2;
 		pos.x += (pos.y ^ shadowData.checkerboard) & 1;
 	}
@@ -156,5 +156,5 @@ void main()
 
 	float shadow = shadowhit ? 0.0 : 1.0;
 
-	imageStore(outImage, ivec2(pos), vec4(shadow, 0, 0, 0));
+	imageStore(outImage, pos, vec4(shadow, 0, 0, 0));
 }

src/shaders/shadowfill.comp.glsl

@@ -7,6 +7,7 @@ layout(local_size_x = 8, local_size_y = 8, local_size_z = 1) in;
 layout(push_constant) uniform block
 {
 	vec2 imageSize;
+	int checkerboard;
 };
 
 layout(binding = 0, r8) uniform image2D shadowImage;
@@ -16,9 +17,9 @@ void main()
 {
 	ivec2 pos = ivec2(gl_GlobalInvocationID.xy);
 
-	// checkerboard odd
+	// checkerboard (opposite)
 	pos.x *= 2;
-	pos.x += pos.y & 1;
+	pos.x += ~(pos.y ^ checkerboard) & 1;
 
 	float depth = texelFetch(depthImage, pos, 0).r;