给顶点着色器传 可变变量, 可以给 片段着色器传值, 颜色值会插值.
<style>
body {
margin: 0;
}
canvas {
width: 100vw;
height: 100vh;
display: block;
}
</style>
<canvas id="c"></canvas>
<script id="vertex-shader-2d" type="notjs">
// an attribute will receive data from a buffer
attribute vec4 a_position;
// all shaders have a main function
void main() {
// gl_Position is a special variable a vertex shader
// is responsible for setting
gl_Position = a_position;
}
</script>
<script id="fragment-shader-2d" type="notjs">
// fragment shaders don't have a default precision so we need
// to pick one. mediump is a good default
precision mediump float;
void main() {
// gl_FragColor is a special variable a fragment shader
// is responsible for setting
gl_FragColor = vec4(1, 0, 0.5, 1); // return redish-purple
}
</script><!--
for most samples webgl-utils only provides shader compiling/linking and
canvas resizing because why clutter the examples with code that's the same in every sample.
See https://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and https://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<script src="https://webglfundamentals.org/webgl/resources/webgl-utils.js"></script>
/* eslint no-console:0 consistent-return:0 */
"use strict";
function createShader(gl, type, source) {
var shader = gl.createShader(type);
gl.shaderSource(shader, source);
gl.compileShader(shader);
var success = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
if (success) {
return shader;
}
console.log(gl.getShaderInfoLog(shader));
gl.deleteShader(shader);
}
function createProgram(gl, vertexShader, fragmentShader) {
var program = gl.createProgram();
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);
var success = gl.getProgramParameter(program, gl.LINK_STATUS);
if (success) {
return program;
}
console.log(gl.getProgramInfoLog(program));
gl.deleteProgram(program);
}
function main() {
// Get A WebGL context
var canvas = document.querySelector("#c");
var gl = canvas.getContext("webgl");
if (!gl) {
return;
}
// Get the strings for our GLSL shaders
var vertexShaderSource = document.querySelector("#vertex-shader-2d").text;
var fragmentShaderSource = document.querySelector("#fragment-shader-2d").text;
// create GLSL shaders, upload the GLSL source, compile the shaders
var vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
var fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);
// Link the two shaders into a program
var program = createProgram(gl, vertexShader, fragmentShader);
// look up where the vertex data needs to go.
var positionAttributeLocation = gl.getAttribLocation(program, "a_position");
// Create a buffer and put three 2d clip space points in it
var positionBuffer = gl.createBuffer();
// Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
var positions = [
0, 0,
0, 0.5,
0.7, 0,
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);
// code above this line is initialization code.
// code below this line is rendering code.
webglUtils.resizeCanvasToDisplaySize(gl.canvas);
// Tell WebGL how to convert from clip space to pixels
gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
// Clear the canvas
gl.clearColor(0, 0, 0, 0);
gl.clear(gl.COLOR_BUFFER_BIT);
// Tell it to use our program (pair of shaders)
gl.useProgram(program);
// Turn on the attribute
gl.enableVertexAttribArray(positionAttributeLocation);
// Bind the position buffer.
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
// Tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER)
var size = 2; // 2 components per iteration
var type = gl.FLOAT; // the data is 32bit floats
var normalize = false; // don't normalize the data
var stride = 0; // 0 = move forward size * sizeof(type) each iteration to get the next position
var offset = 0; // start at the beginning of the buffer
gl.vertexAttribPointer(
positionAttributeLocation, size, type, normalize, stride, offset);
// draw
var primitiveType = gl.TRIANGLES;
var offset = 0;
var count = 3;
gl.drawArrays(primitiveType, offset, count);
}
main();
可以一直画 (画50个矩形)
var colorUniformLocation = gl.getUniformLocation(program, "u_color");
...
// 绘制50个随机颜色矩形
for (var ii = 0; ii < 50; ++ii) {
// 创建一个随机矩形
// 并将写入位置缓冲
// 因为位置缓冲是我们绑定在
// `ARRAY_BUFFER`绑定点上的最后一个缓冲
setRectangle(
gl, randomInt(300), randomInt(300), randomInt(300), randomInt(300));
// 设置一个随机颜色
gl.uniform4f(colorUniformLocation, Math.random(), Math.random(), Math.random(), 1);
// 绘制矩形
gl.drawArrays(gl.TRIANGLES, 0, 6);
}
}
// 返回 0 到 range 范围内的随机整数
function randomInt(range) {
return Math.floor(Math.random() * range);
}
// 用参数生成矩形顶点并写进缓冲
function setRectangle(gl, x, y, width, height) {
var x1 = x;
var x2 = x + width;
var y1 = y;
var y2 = y + height;
// 注意: gl.bufferData(gl.ARRAY_BUFFER, ...) 将会影响到
// 当前绑定点`ARRAY_BUFFER`的绑定缓冲
// 目前我们只有一个缓冲,如果我们有多个缓冲
// 我们需要先将所需缓冲绑定到`ARRAY_BUFFER`
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
x1, y1,
x2, y1,
x1, y2,
x1, y2,
x2, y1,
x2, y2]), gl.STATIC_DRAW);
}
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