先思考个问题, 想实现遮罩怎么办?
<!doctype html>
<html>
<head>
<meta charset="utf-8" />
<title>Stencil Buffer</title>
<script id="shader-vs" type="x-shader/x-vertex">
precision highp float;
attribute vec3 aPos;
attribute vec4 aColor;
varying vec4 vColor;
void main(void){
gl_Position = vec4(aPos, 1);
vColor = aColor;
}
</script>
<script id="shader-fs" type="x-shader/x-fragment">
precision highp float;
varying vec4 vColor;
void main(void) {
gl_FragColor = vColor;
}
</script>
<script id="shader-vs-2" type="x-shader/x-vertex">
precision highp float;
attribute vec3 aPos;
attribute vec2 aTextureCoords;
varying vec2 vTextureCoord;
void main(void){
gl_Position = vec4(aPos, 1.0);
vTextureCoord = aTextureCoords;
}
</script>
<script id="shader-fs-2" type="x-shader/x-fragment">
precision highp float;
varying vec2 vTextureCoord;
uniform sampler2D uSampler;
void main(void) {
gl_FragColor = texture2D(uSampler, vec2(vTextureCoord.s, vTextureCoord.t));
if (gl_FragColor.a == 0.0) {
discard;
}
}
</script>
</head>
<body>
<canvas id="canvas" width="400" height="400" ></canvas>
<script>
var gl;
var canvas = document.getElementById(‘canvas‘);
var glProgram = null;
var glProgram2 = null;
var samplerUniform = null;
var maskTexture;
function getGLContext() {
var glContextNames = [‘webgl‘, ‘experimental-webgl‘];
for (var i = 0; i < glContextNames.length; i ++) {
try {
gl = canvas.getContext(glContextNames[i], {
stencil: true
});
} catch (e) {}
if (gl) {
gl.clearColor(74 / 255, 115 / 255, 94 / 255, 1.0);
gl.clear(gl.COLOR_BUFFER_BIT | gl.STENCIL_BUFFER_BIT);
gl.viewport(0, 0, canvas.width, canvas.height);
gl.enable(gl.STENCIL_TEST);
break;
}
}
}
function initShaders(vsShaderId, fsShaderId) {
//get shader source
var vs_source = document.getElementById(vsShaderId).innerHTML;
var fs_source = document.getElementById(fsShaderId).innerHTML;
//compile shaders
var vertexShader = makeShader(vs_source, gl.VERTEX_SHADER);
var fragmentShader = makeShader(fs_source, gl.FRAGMENT_SHADER);
//create program
var 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);
return 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;
}
// vertex representing the triangle
var vertex = [
-.5, -.2, 0,
.5, -.2, 0,
0, .6, 0
];
var stencilVertex = [
-.2, -.5, 0,
.4, -.5, 0,
.3, .6, 0
];
function setupBufferAndDraw(){
// draw the mask image as stencil
gl.useProgram(program2);
var maskVertex = [
-1, -1, 0,
1, -1, 0,
1, 1, 0,
-1, -1, 0,
1, 1, 0,
-1, 1, 0
];
var maskTexCoords = [
0, 0,
1, 0,
1, 1,
0, 0,
1, 1,
0, 1
];
var maskBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, maskBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(maskVertex), gl.STATIC_DRAW);
var aMaskVertexPosition = gl.getAttribLocation(program2, ‘aPos‘);
gl.vertexAttribPointer(aMaskVertexPosition, 3, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(aMaskVertexPosition);
// texture coordinate data
var maskTexCoordBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, maskTexCoordBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(maskTexCoords), gl.STATIC_DRAW);
var vertexTexCoordAttribute = gl.getAttribLocation(program2, "aTextureCoords");
gl.enableVertexAttribArray(vertexTexCoordAttribute);
gl.vertexAttribPointer(vertexTexCoordAttribute, 2, gl.FLOAT, false, 0, 0);
// Always pass test
gl.stencilFunc(gl.ALWAYS, 1, 0xff);
gl.stencilOp(gl.KEEP, gl.KEEP, gl.REPLACE);
gl.stencilMask(0xff);
gl.clear(gl.STENCIL_BUFFER_BIT);
// No need to display the triangle
gl.colorMask(0, 0, 0, 0);
gl.activeTexture(gl.TEXTURE0);
gl.bindTexture(gl.TEXTURE_2D, maskTexture);
gl.uniform1i(samplerUniform, 0);
gl.drawArrays(gl.TRIANGLES, 0, maskVertex.length / 3);
// return;
gl.useProgram(program);
// Pass test if stencil value is 1
gl.stencilFunc(gl.EQUAL, 1, 0xFF);
gl.stencilMask(0x00);
gl.colorMask(1, 1, 1, 1);
// draw the clipped triangle
var color = [
1, 0, 0, 1,
0, 1, 0, 1,
0, 0, 1, 1
];
var colorBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(color), gl.STATIC_DRAW);
var aColorPosition = gl.getAttribLocation(program, ‘aColor‘);
gl.vertexAttribPointer(aColorPosition, 4, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(aColorPosition);
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(program, ‘aPos‘);
gl.vertexAttribPointer(aVertexPosition, 3, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(aVertexPosition);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.drawArrays(gl.TRIANGLES, 0, vertex.length / 3);
}
function createTexture(source) {
var texture = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D, texture);
gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, true);
gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, source);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
gl.bindTexture(gl.TEXTURE_2D, null);
return texture;
}
window.onload = function () {
getGLContext();
program = initShaders(‘shader-vs‘, ‘shader-fs‘);
program2 = initShaders(‘shader-vs-2‘, ‘shader-fs-2‘);
samplerUniform = gl.getUniformLocation(program2, ‘uSampler‘);
var img = new Image();
img.onload = function () {
maskTexture = createTexture(this);
setupBufferAndDraw();
};
img.src = ‘../images/mask-png8.png‘;
}
</script>
</body>
</html>
原文地址：https://www.cnblogs.com/honghong87/p/9758929.html
时间： 2024-10-24 01:59:52