backend/libs/three/renderers/webgl/WebGLIndexedBufferRenderer.js

function WebGLIndexedBufferRenderer(gl, extensions, info, capabilities) {
	const isWebGL2 = capabilities.isWebGL2;

	let mode;

	function setMode(value) {
		mode = value;
	}

	let type, bytesPerElement;

	function setIndex(value) {
		type = value.type;
		bytesPerElement = value.bytesPerElement;
	}

	function render(start, count) {
		gl.drawElements(mode, count, type, start * bytesPerElement);

		info.update(count, mode, 1);
	}

	function renderInstances(start, count, primcount) {
		if (primcount === 0) return;

		let extension, methodName;

		if (isWebGL2) {
			extension = gl;
			methodName = 'drawElementsInstanced';
		} else {
			extension = extensions.get('ANGLE_instanced_arrays');
			methodName = 'drawElementsInstancedANGLE';

			if (extension === null) {
				console.error(
					'THREE.WebGLIndexedBufferRenderer: using THREE.InstancedBufferGeometry but hardware does not support extension ANGLE_instanced_arrays.'
				);
				return;
			}
		}

		extension[methodName](mode, count, type, start * bytesPerElement, primcount);

		info.update(count, mode, primcount);
	}

	//

	this.setMode = setMode;
	this.setIndex = setIndex;
	this.render = render;
	this.renderInstances = renderInstances;
}

export { WebGLIndexedBufferRenderer };