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webgl-2d-rectangle.html
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<!-- Licensed under a BSD license. See license.html for license -->
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
<title>WebGL - 2D Rectangle</title>
<link type="text/css" href="resources/webgl-tutorials.css" rel="stylesheet" />
</head>
<body>
<canvas id="c"></canvas>
</body>
<!--
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="resources/webgl-utils.js"></script>
<!-- vertex shader -->
<script id="vertex-shader-2d" type="notjs">
attribute vec4 a_position;
uniform vec2 u_resolution;
void main() {
// convert the position from pixels to 0.0 to 1.0
vec2 zeroToOne = a_position.xy / u_resolution;
// convert from 0->1 to 0->2
vec2 zeroToTwo = zeroToOne * 2.0;
// convert from 0->2 to -1->+1 (clipspace)
vec2 clipSpace = zeroToTwo - 1.0;
gl_Position = vec4(clipSpace, 0, 1);
}
</script>
<!-- fragment shader -->
<script id="fragment-shader-2d" type="notjs">
precision mediump float;
void main() {
gl_FragColor = vec4(1, 0, 0.5, 1); // return redish-purple
}
</script>
<script>
"use strict";
function main() {
// Get A WebGL context
var canvas = document.querySelector("#c");
var gl = canvas.getContext("webgl");
if (!gl) {
return;
}
// Use our boilerplate utils to compile the shaders and link into a program
var program = webglUtils.createProgramFromScripts(gl, ["vertex-shader-2d", "fragment-shader-2d"]);
// look up where the vertex data needs to go.
var positionAttributeLocation = gl.getAttribLocation(program, "a_position");
// look up uniform locations
var resolutionUniformLocation = gl.getUniformLocation(program, "u_resolution");
// Create a buffer to put three 2d clip space points in
var positionBuffer = gl.createBuffer();
// Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
var positions = [
10, 20,
80, 20,
10, 30,
10, 30,
80, 20,
80, 30,
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);
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);
// set the resolution
gl.uniform2f(resolutionUniformLocation, gl.canvas.width, gl.canvas.height);
// draw
var primitiveType = gl.TRIANGLES;
var offset = 0;
var count = 6;
gl.drawArrays(primitiveType, offset, count);
}
main();
</script>
</html>