compositeSourceIn: Multiplicative Alpha Masking

Source Visibility Through Destination Alpha Control

The source in composite operation performs multiplicative masking where source color visibility is directly controlled by destination alpha values through multiplication.

$$\text{sourceIn} = src \times \alpha_{dst}$$

ライブエディター

const fragment = () => {
      const center = vec2(0.5, 0.5)
      const dist = uv.distance(center)
      const dstAlpha = smoothstep(0.4, 0.1, dist)
      const srcColor = vec3(1, 0.4, 0.1)
      const src = vec4(srcColor, 1)
      const dst = vec4(vec3(0), dstAlpha)
      return compositeSourceInVec4(src, dst)
}