webglSamples/msaa.html at master · JiaoJianing/webglSamples · GitHub

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<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="utf-8" />
		<title>OffScreen MSAA</title>
		<style>
		</style>
	</head>

	<body onload="main()">
		<canvas id="webgl", width="1920", height="900">
			Please use a browser that supports "canvas"
		</canvas>
		<script src="./lib/webgl-utils.js"></script>
		<script src="./lib/webgl-debug.js"></script>
		<script src="./lib/cuon-utils.js"></script>
		<script src="./lib/cuon-matrix.js"></script>
		<script>
			var VSHADER_SOURCE =
				'attribute vec4 a_Position;'+
				'void main()'+
				'{'+
				'	gl_Position = a_Position;'+
				'}';

			var FSHADER_SOURCE =
				'precision mediump float;'+
				'void main()'+
				'{'+
				'	gl_FragColor = vec4(1.0, 1.0, 0.0, 0.5);'+
				'}';

			function main() {
				var canvas = document.getElementById('webgl');
				if (!canvas){
					console.log('Failed to retrieve the <canvas> element');
					return;
				}

				var gl = getWebGLContext(canvas, {antialias: false});
				if (!gl){
					console.log('Failed to get the rendering context for WebGL');
					return;
				}

				var program = initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE);
				if (!program){
					console.log('Failed to initialize shaders.');
					return;
				}

				//准备多采样的 msFbo
				var msFbo = gl.createFramebuffer();
				var colorRenderbuffer = gl.createRenderbuffer();
				gl.bindRenderbuffer(gl.RENDERBUFFER, colorRenderbuffer);
				gl.renderbufferStorageMultisample(gl.RENDERBUFFER, 8, gl.RGBA8, canvas.width, canvas.height);

				gl.bindFramebuffer(gl.FRAMEBUFFER, msFbo);
				gl.framebufferRenderbuffer(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.RENDERBUFFER, colorRenderbuffer);

				var status = gl.checkFramebufferStatus(gl.FRAMEBUFFER);
				if (status !== gl.FRAMEBUFFER_COMPLETE) {
					console.log("The created frame buffer is invalid: " + status.toString());
				}

				gl.bindFramebuffer(gl.FRAMEBUFFER, null);

				//准备中转的tempFbo
				var tempFbo = gl.createFramebuffer();
				var quadTexture = gl.createTexture();
				gl.bindTexture(gl.TEXTURE_2D, quadTexture);
				gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
				gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
				gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, canvas.width, canvas.height, 0, gl.RGBA, gl.UNSIGNED_BYTE, null);
				gl.bindTexture(gl.TEXTURE_2D, null);

				gl.bindFramebuffer(gl.FRAMEBUFFER, tempFbo);
				gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, quadTexture, 0);
				status = gl.checkFramebufferStatus(gl.FRAMEBUFFER);
				if (status !== gl.FRAMEBUFFER_COMPLETE) {
					console.log("The created frame buffer is invalid: " + status.toString());
				}
				gl.bindFramebuffer(gl.FRAMEBUFFER, null);

				//准备三角形网格顶点数据
				var vertices = new Float32Array([-0.5, -0.5, 0.5, -0.5, 0.0, 1.0]);
				var vertexBuffer = gl.createBuffer();
				if (!vertexBuffer)
				{
					console.log('Failed to create vertex buffer');
					return;
				}

				gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
				gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);

				var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
				if (a_Position < 0)
				{
					console.log('Failed to get the storage location of a_Position');
					return;
				}

				gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);
				gl.enableVertexAttribArray(a_Position);

				var draw = function() {
					gl.bindFramebuffer(gl.FRAMEBUFFER, msFbo);
					gl.clearColor(0, 0, 0, 1);
					gl.clear(gl.COLOR_BUFFER_BIT);

					gl.drawArrays(gl.TRIANGLES, 0, 3);

					gl.bindFramebuffer(gl.READ_FRAMEBUFFER, msFbo);
					gl.bindFramebuffer(gl.DRAW_FRAMEBUFFER, null);
					gl.blitFramebuffer(0, 0, canvas.width, canvas.height,
						0, 0, canvas.width, canvas.height, gl.COLOR_BUFFER_BIT, gl.NEAREST);
				}

				var tick = function() {
					gl.useProgram(program);
					gl.enable(gl.BLEND);
					gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);
					draw();

					requestAnimationFrame(tick);
				}

				tick();
			}
		</script>
	</body>
</html>