ThreeJS WebGLBufferRenderer DrawCall 源码

function WebGLBufferRenderer( gl, extensions, info, capabilities ) {
	const isWebGL2 = capabilities.isWebGL2;
	let mode;
	function setMode( value ) {
		mode = value;
	}
	//调用 WebGLBufferRenderer#render() 方法进行渲染。如下，就是进行最后的 drawArrays() 调用，将上层创建的 geometry 以及 material(组合起来就叫做 mesh) 渲染到 3D 场景的 canvas 中。
	function render( start, count ) {
		gl.drawArrays( mode, start, count ); 
		info.update( count, mode, 1 );
	}
	function renderInstances( start, count, primcount ) {
		if ( primcount === 0 ) return;
		let extension, methodName;
		if ( isWebGL2 ) {
			extension = gl;
			methodName = 'drawArraysInstanced';
		} else {
			extension = extensions.get( 'ANGLE_instanced_arrays' );
			methodName = 'drawArraysInstancedANGLE';
			if ( extension === null ) {
				console.error(
					'THREE.WebGLBufferRenderer: using THREE.InstancedBufferGeometry but hardware does not support extension ANGLE_instanced_arrays.'
				);
				return;
			}
		}
		extension[ methodName ]( mode, start, count, primcount );
		info.update( count, mode, primcount );
	}
	//
	this.setMode = setMode;
	this.render = render;
	this.renderInstances = renderInstances;
}
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