POM

Texture2D g_TextureMap : register(t0);
SamplerState g_TextureSampler : register(s0);

Texture2D g_HeightMap : register(t1);
SamplerState g_HeightSampler : register(s1);

cbuffer cb_POM : register(b0)
{
    matrix g_WorldViewProj;
    float g_HeightScale;
    float g_NumLayers;
    float2 g_UVOffset;
}

struct VS_INPUT
{
    float4 Position : POSITION;
    float2 TexCoord : TEXCOORD0;
};

struct PS_INPUT
{
    float4 Position : SV_POSITION;
    float2 TexCoord : TEXCOORD0;
};

PS_INPUT VSMain(VS_INPUT input)
{
    PS_INPUT output = (PS_INPUT)0;
    output.Position = mul(input.Position, g_WorldViewProj);
    output.TexCoord = input.TexCoord;
    return output;
}

float2 POMOffset(float2 texCoord, float2 viewDir, float height)
{
    float2 offset = height * viewDir.xy / viewDir.z;
    float2 newTexCoord = texCoord - offset * g_UVOffset;
    return lerp(texCoord, newTexCoord, step(0.0, height));
}

float POMHeight(float2 texCoord, float2 viewDir, float maxHeight)
{
    float2 offset = viewDir.xy / viewDir.z * g_UVOffset;
    float height = 0.0;
    float layerDepth = maxHeight / g_NumLayers;
    float currentDepth = 0.0;
    float2 currentTexCoord = texCoord;
    for (int i = 0; i < g_NumLayers; i++)
    {
        height = texture(g_HeightMap, currentTexCoord).r * g_HeightScale;
        height = lerp(currentDepth, height, step(currentDepth, height));
        if (height > 0.0)
        {
            currentTexCoord = POMOffset(currentTexCoord, viewDir, height);
            currentDepth += layerDepth;
        }
        else
        {
            break;
        }
    }
    return currentDepth;
}

float4 PSMain(PS_INPUT input) : SV_Target
{
    float3 viewDir = normalize(float3(input.TexCoord - 0.5, 1.0));
    float height = POMHeight(input.TexCoord, viewDir.xy, 1.0);
    float2 texCoord = POMOffset(input.TexCoord, viewDir.xy, height);
    float4 color = texture(g_TextureMap, texCoord);
    return color;
}