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/shadowmapomni/scene.frag

@@ -0,0 +1,43 @@
+// Copyright 2020 Google LLC
+
+TextureCube shadowCubeMapTexture : register(t1);
+SamplerState shadowCubeMapSampler : register(s1);
+
+struct VSOutput
+{
+[[vk::location(0)]] float3 Normal : NORMAL0;
+[[vk::location(1)]] float3 Color : COLOR0;
+[[vk::location(2)]] float3 EyePos : POSITION0;
+[[vk::location(3)]] float3 LightVec : TEXCOORD2;
+[[vk::location(4)]] float3 WorldPos : POSITION1;
+[[vk::location(5)]] float3 LightPos : POSITION2;
+};
+
+#define EPSILON 0.15
+#define SHADOW_OPACITY 0.5
+
+float4 main(VSOutput input) : SV_TARGET
+{
+	// Lighting
+	float3 N = normalize(input.Normal);
+	float3 L = normalize(float3(1.0, 1.0, 1.0));
+
+	float3 Eye = normalize(-input.EyePos);
+	float3 Reflected = normalize(reflect(-input.LightVec, input.Normal));
+
+	float4 IAmbient = float4(float3(0.05, 0.05, 0.05), 1.0);
+	float4 IDiffuse = float4(1.0, 1.0, 1.0, 1.0) * max(dot(input.Normal, input.LightVec), 0.0);
+
+	float4 outFragColor = float4(IAmbient + IDiffuse * float4(input.Color, 1.0));
+
+	// Shadow
+	float3 lightVec = input.WorldPos - input.LightPos;
+    float sampledDist = shadowCubeMapTexture.Sample(shadowCubeMapSampler, lightVec).r;
+    float dist = length(lightVec);
+
+	// Check if fragment is in shadow
+    float shadow = (dist <= sampledDist + EPSILON) ? 1.0 : SHADOW_OPACITY;
+
+	outFragColor.rgb *= shadow;
+	return outFragColor;
+}