@ygjack 看著像是裸 webgl
```
let canvas = document.createElement("canvas");
this.canvas = canvas;
let gl = canvas.getContext('experimental-webgl', { antialias: true });

gl.getExtension('OES_element_index_uint');
gl.getExtension('OES_standard_derivatives');

let ext = gl.getExtension('ANGLE_instanced_arrays');
......
this.begin = function (width, height) {

width *= scale;
height *= scale;
if (width != prev_width || height != prev_height) {
canvas.width = width;
canvas.height = height;
prev_width = width;
prev_height = height;
}

gl.viewport(0, 0, width, height);

gl.disable(gl.BLEND);
gl.depthMask(true);
gl.depthFunc(gl.LEQUAL);
gl.clearColor(0.0, 0.0, 0.0, 0.0);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

// gl.enable(gl.CULL_FACE);
// gl.cullFace(gl.BACK);
gl.enable(gl.DEPTH_TEST);
gl.blendFunc(gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
```