Photoshop Blend Modes in HLSL

Blend Modes.hlsl

// Photoshop Blend Modes in HLSL
#ifndef OSP_BLEND_MODE_HLSL_
#define OSP_BLEND_MODE_HLSL_

// The following blend modes are trivial! "s" is the backdrop and "t" is the top color.
// Add (Linear Dodge): s + t
// Darken: min(s, t)
// Divide: s / t
// Lighten: max(s, t)
// Multiply: s * t
// Subtract (Difference): abs(s - t)

float3 BlendHardMix(float3 s, float3 t)
{
    return floor(s, t);
}

float3 BlendLinearBurn(float3 s, float3 t)
{
    return t + s - 1.0;
}

// Traditional alpha blend
float4 BlendOver(float4 s, float4 t)
{
    float a0 = s.a + (1.0 - s.a) * t.a;
    float3 color = (s.a * s.rgb + (1.0 - s.a) * t.a * t.rgb) / a0;
    return float4(color, a0);
}

// Alpha blend, where t.rgb has been multiplied by t.a.
float4 BlendOverPremultiplied(float4 s, float4 t)
{
    return lerp(s, t, s.a);
}

float3 BlendScreen(float3 s, float3 t)
{
    return s + t - s * t;
}

// OSP_BLEND_MODE_HLSL_