/** Every mode this can evaluate, which is every one canvas has. */
export declare const BLEND_MODES: readonly string[];
/**
 * The source over the destination with a blend applied, computed rather than
 * left to fixed function factors.
 *
 * Canvas composites a blended mark as `as*(1-ab)*Cs + as*ab*B(Cb,Cs) +
 * (1-as)*ab*Cb`. One set of factors reaches the destination or weights the
 * source by its own alpha, not both, so multiply and screen come out exact only
 * because their algebra happens to fold, and min and max have no term to
 * interpolate with at all: darken and lighten are wrong wherever the source is
 * not fully opaque, which includes every antialiased edge.
 *
 * The mark is drawn into a layer of its own instead, the frame is copied out
 * beneath it, and this evaluates the formula on the two and replaces the pixel.
 */
export declare const blendCompositeShader: (blend: string) => string;