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<!DOCTYPE html>
<head>
<meta charset="utf-8"/>
<title>Колело на цветовете</title>
<script src="webgl-fmi.js"></script>
<script id="vshader" type="x-shader/x-vertex">
attribute vec2 aXY;
attribute vec3 aRGB;
varying vec3 vRGB;
void main ()
{
gl_Position = vec4(aXY,0,1);
gl_PointSize = 4.0;
vRGB = aRGB;
}
</script>
<script id="fshader" type="x-shader/x-fragment">
precision mediump float;
varying vec3 vRGB;
void main( )
{
gl_FragColor = vec4(vRGB,1);
}
</script>
<script>
function start( )
{
gl = getContext("picasso");
glprog = getProgram("vshader","fshader");
aXY = gl.getAttribLocation(glprog,"aXY");
aRGB = gl.getAttribLocation(glprog,"aRGB");
gl.clearColor(1,1,1,1);
gl.clear(gl.COLOR_BUFFER_BIT);
// брой сегменти n
var n = 60;
var points = [];
const aspectRatio = 600 / 400;
const r = 0.8;
points.push(0, 0, 1, 1, 1);
const step = 360 / n;
// https://en.wikipedia.org/wiki/HSL_and_HSV#HSV_to_RGB_alternative
function hueToRgbf(n, H) {
var k = (n + H / 60) % 6;
return 1 - Math.max(0, Math.min(k, 4-k, 1));
}
const offset = 90;
for (var i = 0; i < 361; i += step) {
points.push(Math.sin(2 * Math.PI * (i + offset) / 360) * r / aspectRatio, Math.cos(2 * Math.PI * (i + offset) / 360) * r, hueToRgbf(5, i), hueToRgbf(3, i), hueToRgbf(1, i));
}
var buf = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, buf);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(points), gl.STATIC_DRAW);
gl.vertexAttribPointer(aXY, 2, gl.FLOAT, false, 5 * FLOATS, 0);
gl.vertexAttribPointer(aRGB, 3, gl.FLOAT, false, 5 * FLOATS, 2 * FLOATS);
gl.enableVertexAttribArray(aXY);
gl.enableVertexAttribArray(aRGB);
gl.drawArrays(gl.TRIANGLE_FAN, 0, n + 2);
}
</script>
</head>
<body onload="start()">
<h2>Колело на цветовете</h2>
<noscript>
Искаме JavaScript, но няма!
</noscript>
<canvas id="picasso" width="600" height="400" style="border: solid;">
Искаме canvas, но няма!
</canvas>
</body>
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