Added green screen

shaders/greenscreen-key/shader.slang

@@ -0,0 +1,40 @@
+float3 safeNormalize(float3 value)
+{
+	float len = max(length(value), 0.0001);
+	return value / len;
+}
+
+float luma709(float3 color)
+{
+	return dot(color, float3(0.2126, 0.7152, 0.0722));
+}
+
+float4 shadeVideo(ShaderContext context)
+{
+	float4 src = context.sourceColor;
+	float3 color = saturate(src.rgb);
+
+	float3 keyColor = safeNormalize(max(screenColor.rgb, float3(0.0001, 0.0001, 0.0001)));
+	float3 sampleColor = safeNormalize(max(color, float3(0.0001, 0.0001, 0.0001)));
+
+	float chromaDistance = length(sampleColor - keyColor);
+	float matteCenter = threshold - erodeDilate;
+	float matteFeather = max(softness + edgeSoftness, 0.0005);
+	float alpha = smoothstep(matteCenter - matteFeather, matteCenter + matteFeather, chromaDistance);
+
+	alpha = saturate((alpha - clipBlack) / max(clipWhite - clipBlack, 0.0001));
+	alpha = saturate(alpha + edgeBoost);
+
+	float greenExcess = max(0.0, color.g - max(color.r, color.b));
+	float spillReduction = greenExcess * despill;
+
+	float3 despilled = color;
+	despilled.g = max(0.0, despilled.g - spillReduction);
+
+	float neutral = luma709(despilled);
+	despilled.rb += spillReduction * 0.25;
+	despilled = lerp(float3(neutral, neutral, neutral), despilled, 0.92);
+
+	float3 premultiplied = saturate(despilled) * alpha;
+	return float4(premultiplied, alpha);
+}