/**
 * Canvas text never triggers a font download by itself: `ctx.font` silently
 * falls back to a system face while the @font-face is still being fetched, so a
 * chart that switches to a not-yet-loaded family draws — and measures — with the
 * wrong one. Every family the options mention is therefore requested explicitly,
 * and the chart lays out again once the real faces arrive: text metrics decide
 * the geometry of axes, legend and labels.
 */
export interface FontsOptions {
    /**
     * Redraw the chart once a web font it uses has finished loading (on by
     * default). Turning it off keeps the very first frame as the only one — the
     * chart then draws with whatever face the browser has at that moment and
     * never asks for the missing ones, since canvas text loads no fonts on its own.
     */
    autoReload?: boolean;
}
interface FontUsage {
    families: Set<string>;
    weights: Set<string>;
}
/**
 * Watches the faces a chart draws with: `request` pulls in the fonts declared
 * when the options were applied, `recheck` catches the ones the document
 * declares later on.
 */
export declare class FontWatcher {
    /** Families the current options draw with, normalized for comparison. */
    private families;
    /** Faces already accounted for — every other loaded face is news. */
    private seen;
    /**
     * Asks the browser for every font family the options mention and resolves when
     * they are in. `true` means a face actually arrived, i.e. the chart has to be
     * laid out and drawn again.
     */
    request(options: unknown, ...extraFamilies: string[]): Promise<boolean>;
    /**
     * `true` when a face of one of our families has finished loading since the last
     * look — a font the page declared after the chart was built.
     */
    recheck(): boolean;
    /** Marks every loaded face as seen; `true` if one of ours was new. */
    private absorbLoaded;
}
/**
 * Calls `onLoadingDone` every time the document finishes loading a batch of
 * fonts; returns the unsubscribe.
 */
export declare function watchDocumentFonts(onLoadingDone: () => void): () => void;
/** Every `fontFamily`/`fontWeight` reachable in the options tree. */
export declare function collectFontUsage(value: unknown, depth?: number, usage?: FontUsage): FontUsage;
export {};