/**
 * True when the mode has to be evaluated in a shader against a copy of the
 * frame rather than left to the blend state.
 *
 * multiply and screen fold only against an opaque backdrop. The full formula
 * also carries the source over the part of the pixel the backdrop does not
 * cover, and factors that reach the destination cannot carry that as well: a
 * multiply over nothing came out black where canvas draws the source plainly.
 * A frame cleared opaque stays opaque wherever anything draws, since source
 * over leaves the alpha at one, so there the shortcut is exact.
 *
 * A mark that batches its items has to stop batching where this is true. The
 * copy is read once per draw, so two items sharing one would both blend with
 * what was there before either of them, and canvas composites item by item.
 */
export declare function needsBackdrop(key: string, opaqueBackdrop: boolean): boolean;
/** Replaces the pixel, for a composite that has already done the blending. */
export declare const REPLACE: GPUBlendState;
/**
 * The mode to build a pipeline with, given the one it was asked for. A mode the
 * blend state cannot express builds unblended, and `record` then ties the
 * pipeline back to what it stands in for so the queue can lift its draws into a
 * layer. Every pipeline that carries a blend goes through this.
 */
export declare function buildBlend(blend: string, opaqueBackdrop: boolean): {
    blend: string;
    record: (pipeline: GPURenderPipeline) => void;
};
/** The mode a pipeline's draws are composited with, or undefined for the frame. */
export declare function layerMode(pipeline: GPURenderPipeline): string | undefined;
/** Normalizes a mark's blend to one this renderer keys a pipeline by. */
export declare function blendKey(blend: string | null | undefined): string;
export declare function blendState(key: string): GPUBlendState;