blendSoftLight: Adaptive Illumination Blend Mode

Dynamic Light Modulation Through Threshold-Based Composite Function

The soft light blend mode applies illumination effects through a conditional function that switches between two mathematical regions. For blend values below 0.5, it applies a multiply-like darkening operation. For blend values above 0.5, it performs a screen-like brightening operation using square root transformation.

The mathematical definition involves a threshold function:

$$\text{softLight}(base, blend) = \begin{cases} 2 \cdot base \cdot blend + base^2 \cdot (1 - 2 \cdot blend) & \text{if } blend < 0.5 \\ \sqrt{base} \cdot (2 \cdot blend - 1) + 2 \cdot base \cdot (1 - blend) & \text{if } blend \geq 0.5 \end{cases}$$

The lower region combines linear multiplication with quadratic base enhancement, while the upper region employs square root luminance extraction for gentle brightening transitions.

ライブエディター

const fragment = () => {
      const baseGrad = vec3(uv.x, uv.y, uv.x.mul(uv.y))
      const blendValue = iTime.mul(0.3).sin().mul(0.5).add(0.5)
      const blendVec = vec3(blendValue)
      const boundary = float(0.5).step(uv.y)
      const original = baseGrad.mix(vec3(0.2, 0.4, 0.8), boundary)
      const processed = blendSoftLightVec3(original, blendVec)
      const splitScreen = uv.x.lessThan(0.5).toFloat()
      return vec4(original.mix(processed, splitScreen), 1)
}