Additive vs Alpha Blending
Two ways particles combine with the scene
Also known as: Additive blending · Alpha blend particles · Additive particles · Premultiplied alpha · Translucent vs additive · Additive vs translucent
Definition
Additive and alpha blending are the two main ways particles are combined with what is behind them. Additive adds the particle's color to the image, so it can only brighten, which suits fire, sparks, lasers, glows and magic, and the result does not depend on the drawing order. Alpha blending mixes the particle with the background by opacity, so it can also darken, which suits smoke, dust, mist and clouds, but it needs correct sorting and costs overdraw.
In production
Choose additive for light-emitting effects, where the black parts of the texture disappear, and alpha for effects with solid, dark or opaque-looking parts. Many fires use both: an alpha blended smoke layer under an additive flame layer. Premultiplied alpha lets a single texture do both, which some pipelines use for smoke that glows. In bright scenes additive effects lose contrast and may need alpha instead.
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Tools that use Additive vs Alpha Blending
See also
Blend Mode
How a material combines with what is behind it
Overdraw
Redrawing same pixels
Particles Render in the Wrong Order
Effects pop in front or behind each other
Alpha Channel
Fourth channel that stores transparency or a mask
Bloom
Soft glow around bright pixels
Particle System
Spawns and animates many small elements