先上例子
<!doctype html>
<html>
<head>
<meta charset="utf-8" />
<title>Basic Draw Blend</title>
<script id="shader-vs" type="x-shader/x-vertex">
attribute vec3 aPos;
void main(void){
gl_Position = vec4(aPos, 1);
}
</script>
<script id="shader-fs" type="x-shader/x-fragment">
void main(void) {
gl_FragColor = vec4(1.0, 1.0, 1.0, 0.5);
}
</script>
</head>
<body>
<canvas id="canvas" width="400" height="400" ></canvas>
<script>
var gl;
var canvas = document.getElementById('canvas');
var glProgram = null; function getGLContext() {
var glContextNames = ['webgl', 'experimental-webgl'];
for (var i = 0; i < glContextNames.length; i ++) {
try {
gl = canvas.getContext(glContextNames[i]);
} catch (e) {}
if (gl) {
gl.clearColor(74 / 255, 115 / 255, 94 / 255, 1.0);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.viewport(0, 0, canvas.width, canvas.height);
gl.enable(gl.BLEND);
break;
}
}
} function initShaders() {
//get shader source
var vs_source = document.getElementById('shader-vs').innerHTML,
fs_source = document.getElementById('shader-fs').innerHTML; //compile shaders
vertexShader = makeShader(vs_source, gl.VERTEX_SHADER);
fragmentShader = makeShader(fs_source, gl.FRAGMENT_SHADER); //create program
glProgram = gl.createProgram(); //attach and link shaders to the program
gl.attachShader(glProgram, vertexShader);
gl.attachShader(glProgram, fragmentShader);
gl.linkProgram(glProgram); if (!gl.getProgramParameter(glProgram, gl.LINK_STATUS)) {
alert("Unable to initialize the shader program.");
} //use program
gl.useProgram(glProgram);
} function makeShader(src, type) {
//compile the vertex shader
var shader = gl.createShader(type);
gl.shaderSource(shader, src);
gl.compileShader(shader); if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
alert("Error compiling shader: " + gl.getShaderInfoLog(shader));
}
return shader;
} function setupBuffer(){
// vertex representing the triangle
var vertex = [
-.5, -.3, 0,
.5, -.3, 0,
.5, .3, 0,
-.5, -.3, 0,
.5, .3, 0,
-.5, .3, 0
];
var vertexBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertex), gl.STATIC_DRAW); var aVertexPosition = gl.getAttribLocation(glProgram, 'aPos');
// point the attribute to the currently bound vertex buffer.
gl.vertexAttribPointer(aVertexPosition, 3, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(aVertexPosition);
} function draw(){
gl.drawArrays(gl.TRIANGLES, 0, 6);
} window.onload = function(){
getGLContext();
initShaders();
gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);
// gl.blendFunc(gl.ONE_MINUS_SRC_COLOR, gl.DST_ALPHA);
setupBuffer();
draw();
}
</script>
</body>
</html>