/**
 * scale a canvas to a fixed dpi or window.devicePixelRatio
 * adapted from https://github.com/mhkeller/layercake/blob/main/src/lib/scaleCanvas.js
 * and https://github.com/observablehq/stdlib/blob/main/src/dom/context2d.js
 * @param {HTMLCanvasElement} canvas
 * @param {number} width
 * @param {number} height
 * @param {undefined | number} dpi
 * @returns {{ width: number, height: number }}
 */
export function scale_canvas(canvas: HTMLCanvasElement, width: number, height: number, dpi: undefined | number): {
    width: number;
    height: number;
};