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quad.html
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<!-- vim: sw=4 ts=4 expandtab smartindent ft=javascript
-->
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>WebGL Demo</title>
<style> document, body { margin: 0px; padding: 0px; overflow: hidden; } </style>
</head>
<body>
<canvas id="glcanvas"></canvas>
<script>
function mat4_create() {
let out = new Float32Array(16);
out[0] = 1;
out[5] = 1;
out[10] = 1;
out[15] = 1;
return out;
}
function mat4_ortho(out, left, right, bottom, top, near, far) {
let lr = 1 / (left - right);
let bt = 1 / (bottom - top);
let nf = 1 / (near - far);
out[0] = -2 * lr;
out[1] = 0;
out[2] = 0;
out[3] = 0;
out[4] = 0;
out[5] = -2 * bt;
out[6] = 0;
out[7] = 0;
out[8] = 0;
out[9] = 0;
out[10] = 2 * nf;
out[11] = 0;
out[12] = (left + right) * lr;
out[13] = (top + bottom) * bt;
out[14] = (far + near) * nf;
out[15] = 1;
return out;
}
const pMatrix = mat4_create();
const canvas = document.getElementById('glcanvas');
const gl = canvas.getContext('webgl', {antialias: true});
if (!gl) { alert('Failed to initialize WebGL'); }
(window.onresize = () => {
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
/* account for e.g. high-retina macbook screens */
if (window.devicePixelRatio > 1) {
canvas.style.width = `${canvas.width}px`;
canvas.style.height = `${canvas.height}px`;
canvas.width *= window.devicePixelRatio;
canvas.height *= window.devicePixelRatio;
}
mat4_ortho(pMatrix, 0, gl.canvas.width, gl.canvas.height, 0, 1, -1);
gl.viewport(
0,
0,
canvas.width,
canvas.height
);
})();
const geo_vbuf_pos = gl.createBuffer();
const geo_vbuf_color = gl.createBuffer();
const geo_ibuf = gl.createBuffer();
let shaders;
/* compile shaders */
{
const vs_geo = `
attribute vec3 a_pos;
attribute vec4 a_color;
uniform mat4 u_matrix;
varying vec4 v_color;
void main() {
gl_Position = u_matrix * vec4(a_pos.xyz, 1);
v_color = a_color;
}`;
const fs_geo = `
precision mediump float;
varying vec4 v_color;
void main() {
gl_FragColor = v_color;
}`;
function createProgram(gl, vertexSource, fragmentSource) {
function createShader(gl, type, source) {
const shader = gl.createShader(type);
gl.shaderSource(shader, source);
gl.compileShader(shader);
if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
throw new Error(gl.getShaderInfoLog(shader));
}
return shader;
}
const program = gl.createProgram();
const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexSource);
const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentSource);
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);
if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
throw new Error(gl.getProgramInfoLog(program));
}
const wrapper = {program};
const numAttributes = gl.getProgramParameter(program, gl.ACTIVE_ATTRIBUTES);
for (let i = 0; i < numAttributes; i++) {
const attribute = gl.getActiveAttrib(program, i);
wrapper[attribute.name] = gl.getAttribLocation(program, attribute.name);
}
const numUniforms = gl.getProgramParameter(program, gl.ACTIVE_UNIFORMS);
for (let i = 0; i < numUniforms; i++) {
const uniform = gl.getActiveUniform(program, i);
wrapper[uniform.name] = gl.getUniformLocation(program, uniform.name);
}
return wrapper;
}
shaders = {
geo: createProgram(gl, vs_geo, fs_geo)
}
}
requestAnimationFrame(function frame(timestamp) {
requestAnimationFrame(frame);
const geo_idx = [];
const geo_pos = [];
const geo_color = [];
function drawSquare( min_x, min_y, max_x, max_y, z, color ) {
geo_color.push(
color[0], color[1], color[2], color[3],
color[0], color[1], color[2], color[3],
color[0], color[1], color[2], color[3],
color[0], color[1], color[2], color[3]
)
const vbuf_i = geo_pos.length / 3;
geo_pos.push(max_x, min_y, z);
geo_pos.push(min_x, min_y, z);
geo_pos.push(min_x, max_y, z);
geo_pos.push(max_x, max_y, z);
geo_idx.push(vbuf_i + 0, vbuf_i + 1, vbuf_i + 2, vbuf_i + 2, vbuf_i + 3, vbuf_i + 0);
}
{
const rainbow = [
/* red, */ [255, 0, 0, 255],
/* orange, */ [255, 100, 0, 255],
/* yellow, */ [255, 255, 0, 255],
/* green, */ [ 0, 255, 0, 255],
/* blue, */ [ 0, 0, 255, 255],
/* purple */ [255, 0, 255, 255]
];
/* desaturate */
for (const color of rainbow) {
color[0] = (color[0] + 255*2) * 0.33;
color[1] = (color[1] + 255*2) * 0.33;
color[2] = (color[2] + 255*2) * 0.33;
color[0] *= 0.8;
color[1] *= 0.8;
color[2] *= 0.8;
color[3] *= 0.8;
}
if (1) {
/* front to back */
for (let _i = 0; _i < rainbow.length; _i++) {
const i = rainbow.length - 1 - _i;
const min_x = 500 + i* 75;
const min_y = 500 + i* 75;
const max_x = min_x + 200;
const max_y = min_y + 200;
const z = (i/rainbow.length)*2 - 1;
drawSquare(min_x, min_y, max_x, max_y, z, rainbow[i]);
}
} else {
/* back to font */
for (let i = 0; i < rainbow.length; i++) {
const min_x = 500 + i* 75;
const min_y = 500 + i* 75;
const max_x = min_x + 200;
const max_y = min_y + 200;
const z = (1 - i/rainbow.length)*2 - 1;
drawSquare(min_x, min_y, max_x, max_y, z, rainbow[i]);
}
}
}
{
/* set up premultiplied alpha */
gl.blendFunc(gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
gl.enable(gl.BLEND);
gl.enable(gl.DEPTH_TEST);
gl.depthFunc(gl.LEQUAL);
/* clear all */
gl.clearColor(1, 1, 1, 1);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
/* geo pass */
{
gl.useProgram(shaders.geo.program);
gl.enableVertexAttribArray(shaders.geo.a_pos);
gl.enableVertexAttribArray(shaders.geo.a_color);
gl.uniformMatrix4fv(shaders.geo.u_matrix, false, pMatrix);
/* upload/bind geometry */
{
gl.bindBuffer(gl.ARRAY_BUFFER, geo_vbuf_pos);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(geo_pos), gl.STATIC_DRAW);
gl.vertexAttribPointer(shaders.geo.a_pos, 3, gl.FLOAT, false, 0, 0);
gl.bindBuffer(gl.ARRAY_BUFFER, geo_vbuf_color);
gl.bufferData(gl.ARRAY_BUFFER, new Uint8Array(geo_color), gl.STATIC_DRAW);
gl.vertexAttribPointer(shaders.geo.a_color, 4, gl.UNSIGNED_BYTE, true, 0, 0);
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, geo_ibuf);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(geo_idx), gl.STATIC_DRAW);
}
gl.drawElements(gl.TRIANGLES, geo_idx.length, gl.UNSIGNED_SHORT, 0);
}
}
})
</script>
</body>
</html>