Function ComputeLayoutAndAllocationSize

src/video_frame.ts:743–850

(
	parsedRect: DOMRectInit,
	format: VideoPixelFormat,
	layout?: PlaneLayout[],
)

};

const ComputeLayoutAndAllocationSize = (
	parsedRect: DOMRectInit,
	format: VideoPixelFormat,
	layout?: PlaneLayout[],
): CombinedBufferLayout => {
	const info = getPixelFormatInfo(format);
	if (!info) throw new TypeError('Unknown format');

	// 1. Let numPlanes be the number of planes as defined by format.
	const numPlanes = info.planes.length;

	// 2. If layout is not undefined and its length does not equal numPlanes, throw a TypeError.
	if (layout !== undefined && layout.length !== numPlanes) {
		throw new TypeError(`Layout must have ${numPlanes} planes`);
	}

	// 3. Let minAllocationSize be 0.
	let minAllocationSize = 0;

	// 4. Let computedLayouts be a new list.
	const computedLayouts: ComputedPlaneLayout[] = [];

	// 5. Let endOffsets be a new list.
	const endOffsets: number[] = [];

	// 6. Let planeIndex be 0.
	// 7. While planeIndex < numPlanes:
	for (let planeIndex = 0; planeIndex < numPlanes; planeIndex++) {
		const plane = info.planes[planeIndex];
		const sampleBytes = plane.bytesPerSample;
		const sampleWidth = plane.sampleWidth;
		const sampleHeight = plane.sampleHeight;

		// Let computedLayout be a new computed plane layout.
		const computedLayout: ComputedPlaneLayout = {
			destinationOffset: 0,
			destinationStride: 0,
			sourceTop: 0,
			sourceHeight: 0,
			sourceLeftBytes: 0,
			sourceWidthBytes: 0,
		};

		// Set computedLayout’s sourceTop...
		computedLayout.sourceTop = Math.ceil(Math.trunc(parsedRect.y || 0) / sampleHeight);
		// Set computedLayout’s sourceHeight...
		computedLayout.sourceHeight = Math.ceil(Math.trunc(parsedRect.height || 0) / sampleHeight);
		// Set computedLayout’s sourceLeftBytes...
		computedLayout.sourceLeftBytes = Math.floor(Math.trunc(parsedRect.x || 0) / sampleWidth) * sampleBytes;
		// Set computedLayout’s sourceWidthBytes...
		computedLayout.sourceWidthBytes = Math.floor(Math.trunc(parsedRect.width || 0) / sampleWidth) * sampleBytes;

		// If layout is not undefined:
		if (layout !== undefined) {
			const planeLayout = layout[planeIndex];
			// If planeLayout.stride is less than computedLayout’s sourceWidthBytes, return a TypeError.
			if (planeLayout.stride < computedLayout.sourceWidthBytes) {
				throw new TypeError(`Stride for plane ${planeIndex} is too small`);