Function buildKTX2Buffer

packages/melonjs/tests/parseKTX2.node-test.js:31–122

* Build a minimal KTX2 binary file in memory.

({
	vkFormat = VK_FORMAT_BC1_RGB_UNORM_BLOCK,
	width = 8,
	height = 8,
	levelCount = 1,
	supercompressionScheme = 0,
	blockBytes = 8,
} = {})

 * Build a minimal KTX2 binary file in memory.
 */
function buildKTX2Buffer({
	vkFormat = VK_FORMAT_BC1_RGB_UNORM_BLOCK,
	width = 8,
	height = 8,
	levelCount = 1,
	supercompressionScheme = 0,
	blockBytes = 8,
} = {}) {
	// Layout:
	// [0..11]   identifier (12 bytes)
	// [12..79]  header (68 bytes) — we use a 68-byte header area
	// [80..]    level index (levelCount × 24 bytes)
	// then pixel data

	const levelIndexOffset = 80;
	const levelIndexSize = levelCount * 24;
	const pixelDataStart = levelIndexOffset + levelIndexSize;

	// calculate level sizes and total pixel data
	const levelSizes = [];
	let lw = width;
	let lh = height;
	for (let i = 0; i < levelCount; i++) {
		const size =
			Math.max(1, (lw + 3) >> 2) * Math.max(1, (lh + 3) >> 2) * blockBytes;
		levelSizes.push(size);
		lw = Math.max(1, lw >> 1);
		lh = Math.max(1, lh >> 1);
	}

	// In KTX2, level 0 in the index is the largest mip
	// Levels are stored in the file smallest-first, but byte offsets handle this
	let totalPixelSize = 0;
	for (const s of levelSizes) {
		totalPixelSize += s;
	}

	const totalSize = pixelDataStart + totalPixelSize;
	const buffer = new ArrayBuffer(totalSize);

	// write identifier
	const idView = new Uint8Array(buffer, 0, 12);
	for (let i = 0; i < 12; i++) {
		idView[i] = KTX2_IDENTIFIER[i];
	}

	// write header at offset 12 (68 bytes)
	const header = new DataView(buffer, 12, 68);
	header.setUint32(0, vkFormat, true); // vkFormat
	// typeSize at +4
	header.setUint32(4, 1, true);
	header.setUint32(8, width, true); // pixelWidth
	header.setUint32(12, height, true); // pixelHeight
	header.setUint32(16, 0, true); // pixelDepth
	header.setUint32(20, 0, true); // layerCount
	header.setUint32(24, 1, true); // faceCount
	header.setUint32(28, levelCount, true); // levelCount
	header.setUint32(32, supercompressionScheme, true);