blendAdd: Additive Color Blending

Mathematical Foundation of Brightness Accumulation

Additive blending increases image brightness by mathematically combining color values through addition. This operation simulates light emission where multiple light sources combine their intensities.

The mathematical definition is:

$$C_{result} = \min(C_{base} + C_{blend}, 1.0)$$

Where $C_{base}$ is the background color, $C_{blend}$ is the overlay color, and the $\min$ function prevents values from exceeding the maximum brightness threshold.

For opacity-controlled blending:

$$C_{result} = \text{blend}(C_{base}, C_{blend}) \times \alpha + C_{base} \times (1 - \alpha)$$

Color Mathematics Properties

Property	Description	Result
Identity	Adding zero preserves original color	$C + 0 = C$
Commutativity	Order independence in addition	$A + B = B + A$
Brightness Increase	Result never darker than base	$\text{brightness}(result) \geq \text{brightness}(base)$
Clamping Behavior	Values saturate at maximum brightness	$\max(result) = 1.0$

ライブエディター

const fragment = () => {
      const center = vec2(0.5)
      const dist = uv.sub(center).length()
      const baseCircle = float(0.35).smoothstep(0.3, dist)
      const blendCircle = float(0.25).smoothstep(0.2, uv.sub(vec2(0.65, 0.4)).length())
      const base = vec3(0.2, 0.4, 0.8).mul(baseCircle)
      const blend = vec3(0.9, 0.3, 0.1).mul(blendCircle)
      const result = blendAddVec3(base, blend)
      return vec4(result, 1)
}

結果

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