I'm trying to do alpha blending manually because I only want to apply alpha blending on certain pixels. Underlying is the texture I'm writing to. This is what I got so far, but it doesn't give the same result as when AlphaBlendEnable = TRUE
What formula does default alpha blend in HLSL use?
matrix WorldViewProjection; texture2D OverlyingShadingMap; sampler2D OverlyingShadingMapSampler = sampler_state { texture = <OverlyingShadingMap>; }; texture2D UnderlyingShadingMap; sampler2D UnderlyingShadingMapSampler = sampler_state { texture = <UnderlyingShadingMap>; }; struct VertexShaderOutput { float4 Position : SV_POSITION; float4 Color : COLOR0; float2 TextureCoordinates : TEXCOORD0; }; VertexShaderOutput SpriteVertexShader(float4 position : POSITION0, float4 color : COLOR0, float2 texCoord : TEXCOORD0) { VertexShaderOutput output; output.Position = mul(position, WorldViewProjection); output.Color = color; output.TextureCoordinates = texCoord; return output; } float4 SpritePixelShader(VertexShaderOutput input) : COLOR { float4 overlying = tex2D(OverlyingShadingMapSampler, input.TextureCoordinates); clip(overlying.a - 0.001); float4 underlying = tex2D(UnderlyingShadingMapSampler, input.TextureCoordinates); // Alphablending float3 rgb = overlying.rgb * overlying.a + (1 - overlying.a) * underlying.a * underlying.rgb; float alpha = underlying.a + (1 - underlying.a) * overlying.a; return float4(rgb, alpha); } technique SpriteDrawing { pass P0 { AlphaBlendEnable = FALSE; VertexShader = compile vs_2_0 SpriteVertexShader(); PixelShader = compile ps_2_0 SpritePixelShader(); } }; 