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/textoverlay/mesh.frag

@@ -0,0 +1,20 @@
+// Copyright 2020 Google LLC
+
+struct VSOutput
+{
+[[vk::location(0)]] float3 Normal : NORMAL0;
+[[vk::location(1)]] float2 UV : TEXCOORD0;
+[[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 V = normalize(input.ViewVec);
+	float3 R = reflect(-L, N);
+	float diffuse = max(dot(N, L), 0.0);
+	float specular = pow(max(dot(R, V), 0.0), 1.0);
+	return float4(((diffuse + specular) * 0.25).xxx, 1.0);
+}

data/hlsl/textoverlay/mesh.vert

@@ -0,0 +1,41 @@
+// Copyright 2020 Google LLC
+
+struct VSInput
+{
+[[vk::location(0)]] float3 Pos : POSITION0;
+[[vk::location(1)]] float3 Normal : NORMAL0;
+[[vk::location(2)]] float2 UV : TEXCOORD0;
+};
+
+struct UBO
+{
+	float4x4 projection;
+	float4x4 model;
+	float4 lightPos;
+};
+
+cbuffer ubo : register(b0) { UBO ubo; }
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] float3 Normal : NORMAL0;
+[[vk::location(1)]] float2 UV : TEXCOORD0;
+[[vk::location(2)]] float3 ViewVec : TEXCOORD1;
+[[vk::location(3)]] float3 LightVec : TEXCOORD2;
+};
+
+VSOutput main(VSInput input)
+{
+	VSOutput output = (VSOutput)0;
+	output.Normal = input.Normal;
+	output.UV = input.UV;
+	output.Pos = mul(ubo.projection, mul(ubo.model, float4(input.Pos.xyz, 1.0)));
+
+	float4 pos = mul(ubo.model, float4(input.Pos, 1.0));
+	output.Normal = mul((float3x3)ubo.model, normalize(input.Normal));
+	float3 lPos = mul((float3x3)ubo.model, ubo.lightPos.xyz);
+	output.LightVec = lPos - pos.xyz;
+	output.ViewVec = -pos.xyz;
+	return output;
+}

data/hlsl/textoverlay/text.frag

@@ -0,0 +1,10 @@
+// Copyright 2020 Google LLC
+
+Texture2D textureFont : register(t0);
+SamplerState samplerFont : register(s0);
+
+float4 main([[vk::location(0)]] float2 inUV : TEXCOORD0) : SV_TARGET
+{
+	float color = textureFont.Sample(samplerFont, inUV).r;
+	return color.xxxx;
+}

data/hlsl/textoverlay/text.vert

@@ -0,0 +1,21 @@
+// Copyright 2020 Google LLC
+
+struct VSInput
+{
+[[vk::location(0)]] float2 Pos : POSITION0;
+[[vk::location(1)]] float2 UV : TEXCOORD0;
+};
+
+struct VSOutput
+{
+	float4 Pos : SV_POSITION;
+[[vk::location(0)]] float2 UV : TEXCOORD0;
+};
+
+VSOutput main(VSInput input)
+{
+	VSOutput output = (VSOutput)0;
+	output.Pos = float4(input.Pos, 0.0, 1.0);
+	output.UV = input.UV;
+	return output;
+}