Function prepareGraph

packages/debug-plugin/src/graphs.js:11–23

* Resize a canvas backing store to match its CSS layout width, clear it, * and return a draw context. Returns `null` if the canvas has no layout * width yet (e.g. panel hidden, first frame). * @param {HTMLCanvasElement} canvas * @returns {{ ctx: CanvasRenderingContext2D, w: number, h: number, ba

(canvas)

 * @returns {{ ctx: CanvasRenderingContext2D, w: number, h: number, barW: number } | null}
 */
function prepareGraph(canvas) {
	const w = canvas.clientWidth;
	if (w === 0) {
		return null;
	}
	if (canvas.width !== w) {
		canvas.width = w;
	}
	const ctx = canvas.getContext("2d");
	const h = GRAPH_HEIGHT;
	ctx.clearRect(0, 0, w, h);
	return { ctx, w, h, barW: w / GRAPH_SAMPLES };
}

/**
 * Round a peak value up to the nearest multiple of 4, with a floor of 4.