Add shaders re-implemented in HLSL

These were written against the shaders at revision eddd724e7.
There have been changes made since then, which will need to be mirrored.

See `data/hlsl/README.md` for the current status of each sample.

data/hlsl/computecullandlod/cull.comp

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+// Copyright 2020 Google LLC
+
+#define MAX_LOD_LEVEL_COUNT 6
+[[vk::constant_id(0)]] const int MAX_LOD_LEVEL = 5;
+
+struct InstanceData
+{
+	float3 pos;
+	float scale;
+};
+
+StructuredBuffer<InstanceData> instances : register(t0);
+
+// Same layout as VkDrawIndexedIndirectCommand
+struct IndexedIndirectCommand
+{
+	uint indexCount;
+	uint instanceCount;
+	uint firstIndex;
+	uint vertexOffset;
+	uint firstInstance;
+};
+
+RWStructuredBuffer<IndexedIndirectCommand> indirectDraws : register(u1);
+
+// Binding 2: Uniform block object with matrices
+struct UBO
+{
+	float4x4 projection;
+	float4x4 modelview;
+	float4 cameraPos;
+	float4 frustumPlanes[6];
+};
+
+cbuffer ubo : register(b2) { UBO ubo; }
+
+// Binding 3: Indirect draw stats
+struct UBOOut
+{
+	uint drawCount;
+	uint lodCount[MAX_LOD_LEVEL_COUNT];
+};
+RWStructuredBuffer<UBOOut> uboOut : register(u3);
+
+// Binding 4: level-of-detail information
+struct LOD
+{
+	uint firstIndex;
+	uint indexCount;
+	float distance;
+	float _pad0;
+};
+
+StructuredBuffer<LOD> lods : register(t4);
+
+[numthreads(16, 1, 1)]
+bool frustumCheck(float4 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;
+}
+
+[numthreads(16, 1, 1)]
+void main(uint3 GlobalInvocationID : SV_DispatchThreadID )
+{
+	uint idx = GlobalInvocationID.x;
+	uint temp;
+
+	// Clear stats on first invocation
+	if (idx == 0)
+	{
+		InterlockedExchange(uboOut[0].drawCount, 0, temp);
+		for (uint i = 0; i < MAX_LOD_LEVEL + 1; i++)
+		{
+			InterlockedExchange(uboOut[0].lodCount[i], 0, temp);
+		}
+	}
+
+	float4 pos = float4(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
+		InterlockedAdd(uboOut[0].drawCount, 1, temp);
+
+		// 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
+		InterlockedAdd(uboOut[0].lodCount[lodLevel], 1, temp);
+	}
+	else
+	{
+		indirectDraws[idx].instanceCount = 0;
+	}
+}

data/hlsl/computecullandlod/indirectdraw.frag

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+// Copyright 2020 Google LLC
+
+struct VSOutput
+{
+[[vk::location(0)]] float3 Normal : NORMAL0;
+[[vk::location(1)]] float3 Color : COLOR0;
+[[vk::location(2)]] float3 ViewVec : TEXCOORD1;
+[[vk::location(3)]] float3 LightVec : TEXCOORD2;
+};
+
+float4 main(VSOutput input) : SV_TARGET
+{
+	float3 N = normalize(input.Normal);
+	float3 L = normalize(input.LightVec);
+	float3 ambient = float3(0.25, 0.25, 0.25);
+	float3 diffuse = max(dot(N, L), 0.0).xxx;
+	return float4((ambient + diffuse) * input.Color, 1.0);
+}

data/hlsl/computecullandlod/indirectdraw.vert

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+// Copyright 2020 Google LLC
+
+struct VSInput
+{
+[[vk::location(0)]] float4 Pos : POSITION0;
+[[vk::location(1)]] float3 Normal : NORMAL0;
+[[vk::location(2)]] float3 Color : COLOR0;
+// Instanced attributes
+[[vk::location(4)]] float3 instancePos : TEXCOORD0;
+[[vk::location(5)]] float instanceScale : TEXCOORD1;
+};
+
+struct UBO
+{
+	float4x4 projection;
+	float4x4 modelview;
+};
+
+cbuffer ubo : register(b0) { UBO ubo; }
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] float3 Normal : NORMAL0;
+[[vk::location(1)]] float3 Color : COLOR0;
+[[vk::location(2)]] float3 ViewVec : TEXCOORD1;
+[[vk::location(3)]] float3 LightVec : TEXCOORD2;
+};
+
+VSOutput main(VSInput input)
+{
+	VSOutput output = (VSOutput)0;
+	output.Color = input.Color;
+
+	output.Normal = input.Normal;
+
+	float4 pos = float4((input.Pos.xyz * input.instanceScale) + input.instancePos, 1.0);
+
+	output.Pos = mul(ubo.projection, mul(ubo.modelview, pos));
+
+	float4 wPos = mul(ubo.modelview, float4(pos.xyz, 1.0));
+	float4 lPos = float4(0.0, 10.0, 50.0, 1.0);
+	output.LightVec = lPos.xyz - pos.xyz;
+	output.ViewVec = -pos.xyz;
+	return output;
+}