Compute shader frustum culling and lod selection example (wip)

data/shaders/computecullandlod/cull.comp

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+#version 450
+
+#extension GL_ARB_separate_shader_objects : enable
+#extension GL_ARB_shading_language_420pack : enable
+
+layout (constant_id = 0) const int MAX_LOD_LEVEL = 5;
+
+struct InstanceData 
+{
+	vec4 pos;
+	vec4 rot;
+};
+
+// Binding 0: Instance input data for culling
+layout (binding = 0, std140) buffer Instances 
+{
+   InstanceData instances[ ];
+};
+
+// Same layout as VkDrawIndexedIndirectCommand
+struct IndexedIndirectCommand 
+{
+	uint indexCount;
+	uint instanceCount;
+	uint firstIndex;
+	uint vertexOffset;
+	uint firstInstance;
+};
+
+// Binding 1: Multi draw output
+layout (binding = 1, std430) writeonly buffer IndirectDraws
+{
+	IndexedIndirectCommand indirectDraws[ ];
+};
+
+// Binding 2: Uniform block object with matrices
+layout (binding = 2) uniform UBO 
+{
+	mat4 projection;
+	mat4 modelview;
+	vec4 cameraPos;
+	vec4 frustumPlanes[6];
+} ubo;
+
+// Binding 3: Indirect draw stats
+layout (binding = 3) buffer UBOOut
+{
+	uint drawCount;
+	uint lodCount[MAX_LOD_LEVEL + 1];
+} uboOut;
+
+// Binding 4: level-of-detail information
+struct LOD
+{
+	uint firstIndex;
+	uint indexCount;
+	float distance;
+	float _pad0;
+};
+layout (binding = 4) readonly buffer LODs
+{
+	LOD lods[ ];
+};
+
+layout (local_size_x = 16) in;
+
+bool frustumCheck(vec4 pos, float radius)
+{
+	// Check sphere against frustum planes
+	for (int i = 0; i < 6; i++) 
+	{
+		if (dot(pos, ubo.frustumPlanes[i]) + radius < 0.0)
+		{
+			return false;
+		}
+	}
+	return true;
+}
+
+layout (local_size_x = 16) in;
+
+void main()
+{
+	uint idx = gl_GlobalInvocationID.x + gl_GlobalInvocationID.y * gl_NumWorkGroups.x * gl_WorkGroupSize.x;
+
+	// Clear stats on first invocation
+	if (idx == 0)
+	{
+		atomicExchange(uboOut.drawCount, 0);
+		for (uint i = 0; i < MAX_LOD_LEVEL + 1; i++)
+		{
+			atomicExchange(uboOut.lodCount[i], 0);
+		}
+	}
+
+	vec4 pos = vec4(instances[idx].pos.xyz, 1.0);
+
+	// Check if object is within current viewing frustum
+	if (frustumCheck(pos, 1.0))
+	{
+		indirectDraws[idx].instanceCount = 1;
+		
+		// Increase number of indirect draw counts
+		atomicAdd(uboOut.drawCount, 1);
+
+		// Select appropriate LOD level based on distance to camera
+		uint lodLevel = MAX_LOD_LEVEL;
+		for (uint i = 0; i < MAX_LOD_LEVEL; i++)
+		{
+			if (distance(instances[idx].pos.xyz, ubo.cameraPos.xyz) < lods[i].distance) 
+			{
+				lodLevel = i;
+				break;
+			}
+		}
+		indirectDraws[idx].firstIndex = lods[lodLevel].firstIndex;
+		indirectDraws[idx].indexCount = lods[lodLevel].indexCount;
+		// Update stats
+		atomicAdd(uboOut.lodCount[lodLevel], 1);
+	}
+	else
+	{
+		indirectDraws[idx].instanceCount = 0;
+	}
+}

data/shaders/computecullandlod/indirectdraw.frag

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+#version 450
+
+#extension GL_ARB_separate_shader_objects : enable
+#extension GL_ARB_shading_language_420pack : enable
+
+layout (location = 0) in vec3 inNormal;
+layout (location = 1) in vec3 inColor;
+layout (location = 2) in vec3 inUV;
+layout (location = 3) in vec3 inViewVec;
+layout (location = 4) in vec3 inLightVec;
+
+layout (location = 0) out vec4 outFragColor;
+
+void main()
+{
+	vec3 N = normalize(inNormal);
+	vec3 L = normalize(inLightVec);
+	vec3 ambient = vec3(0.25);
+	vec3 diffuse = vec3(max(dot(N, L), 0.0));
+	outFragColor = vec4((ambient + diffuse) * inColor, 1.0);
+}

data/shaders/computecullandlod/indirectdraw.vert

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+#version 450
+
+#extension GL_ARB_separate_shader_objects : enable
+#extension GL_ARB_shading_language_420pack : enable
+
+// Vertex attributes
+layout (location = 0) in vec4 inPos;
+layout (location = 1) in vec3 inNormal;
+layout (location = 2) in vec2 inUV;
+layout (location = 3) in vec3 inColor;
+
+// Instanced attributes
+layout (location = 4) in vec3 instancePos;
+layout (location = 5) in vec3 instanceRot;
+layout (location = 6) in float instanceScale;
+layout (location = 7) in float instanceTexIndex;
+
+layout (binding = 0) uniform UBO 
+{
+	mat4 projection;
+	mat4 modelview;
+} ubo;
+
+layout (location = 0) out vec3 outNormal;
+layout (location = 1) out vec3 outColor;
+layout (location = 2) out vec3 outUV;
+layout (location = 3) out vec3 outViewVec;
+layout (location = 4) out vec3 outLightVec;
+
+out gl_PerVertex
+{
+	vec4 gl_Position;
+};
+
+void main() 
+{
+	outColor = inColor;
+	outUV = vec3(inUV, instanceTexIndex);
+	outUV.t = 1.0 - outUV.t;
+		
+	outNormal = inNormal;// * mat3(rotMat);
+	
+	vec4 pos = vec4((inPos.xyz * instanceScale) + instancePos, 1.0)/* rotMat*/;
+
+	gl_Position = ubo.projection * ubo.modelview * pos;
+	
+	vec4 wPos = ubo.modelview * vec4(pos.xyz, 1.0); 
+	vec4 lPos = vec4(0.0, 10.0, 50.0, 1.0);
+	outLightVec = lPos.xyz - pos.xyz;
+	outViewVec = -pos.xyz;	
+}