webgl-lessons

<html>

<head>

<title>Learning WebGL — Mandelbrot shader example</title>

precision mediump float;

varying vec2 vPosition;

void main(void) {

float cx = vPosition.x;

float cy = vPosition.y;

float hue;

float saturation;

float value;

float hueRound;

int hueIndex;

float f;

float p;

float q;

float t;

float x = 0.0;

float y = 0.0;

float tempX = 0.0;

int i = 0;

int runaway = 0;

for (int i=0; i < 100; i++) {

tempX = x * x - y * y + float(cx);

y = 2.0 * x * y + float(cy);

x = tempX;

if (runaway == 0 && x * x + y * y > 100.0) {

runaway = i;

}

if (runaway != 0) {

hue = float(runaway) / 200.0;

saturation = 0.6;

value = 1.0;

hueRound = hue * 6.0;

hueIndex = int(mod(float(int(hueRound)), 6.0));

f = fract(hueRound);

p = value * (1.0 - saturation);

q = value * (1.0 - f * saturation);

t = value * (1.0 - (1.0 - f) * saturation);

if (hueIndex == 0)

gl_FragColor = vec4(value, t, p, 1.0);

else if (hueIndex == 1)

gl_FragColor = vec4(q, value, p, 1.0);

else if (hueIndex == 2)

gl_FragColor = vec4(p, value, t, 1.0);

else if (hueIndex == 3)

gl_FragColor = vec4(p, q, value, 1.0);

else if (hueIndex == 4)

gl_FragColor = vec4(t, p, value, 1.0);

else if (hueIndex == 5)

gl_FragColor = vec4(value, p, q, 1.0);

} else {

gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0);

}

</script>

attribute vec2 aVertexPosition;

attribute vec2 aPlotPosition;

varying vec2 vPosition;

void main(void) {

gl_Position = vec4(aVertexPosition, 1.0, 1.0);

vPosition = aPlotPosition;

}

</script>

var gl;

function initGL(canvas) {

try {

gl = canvas.getContext("experimental-webgl");

gl.viewportWidth = canvas.width;

gl.viewportHeight = canvas.height;

} catch(e) {

}

if (!gl) {

alert("Could not initialise WebGL, sorry :-(");

}

function getShader(gl, id) {

var shaderScript = document.getElementById(id);

if (!shaderScript) {

return null;

}

var str = "";

var k = shaderScript.firstChild;

while (k) {

if (k.nodeType == 3) {

str += k.textContent;

}

k = k.nextSibling;

}

var shader;

if (shaderScript.type == "x-shader/x-fragment") {

shader = gl.createShader(gl.FRAGMENT_SHADER);

} else if (shaderScript.type == "x-shader/x-vertex") {

shader = gl.createShader(gl.VERTEX_SHADER);

} else {

return null;

}

gl.shaderSource(shader, str);

gl.compileShader(shader);

if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {

alert(gl.getShaderInfoLog(shader));

return null;

}

return shader;

}

var shaderProgram;

var aVertexPosition;

function initShaders() {

var fragmentShader = getShader(gl, "shader-fs");

var vertexShader = getShader(gl, "shader-vs");

shaderProgram = gl.createProgram();

gl.attachShader(shaderProgram, vertexShader);

gl.attachShader(shaderProgram, fragmentShader);

gl.linkProgram(shaderProgram);

if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {

alert("Could not initialise shaders");

}

gl.useProgram(shaderProgram);

aVertexPosition = gl.getAttribLocation(shaderProgram, "aVertexPosition");

gl.enableVertexAttribArray(aVertexPosition);

aPlotPosition = gl.getAttribLocation(shaderProgram, "aPlotPosition");

gl.enableVertexAttribArray(aPlotPosition);

}

var centerOffsetX = 0;

var centerOffsetY = 0;

var zoom;

var zoomCenterX;

var zoomCenterY;

var vertexPositionBuffer;

function initBuffers() {

vertexPositionBuffer = gl.createBuffer();

gl.bindBuffer(gl.ARRAY_BUFFER, vertexPositionBuffer);

var vertices = [

1.0, 1.0,

-1.0, 1.0,

1.0, -1.0,

-1.0, -1.0,

];

gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);

vertexPositionBuffer.itemSize = 2;

vertexPositionBuffer.numItems = 4;

}

var baseCorners = [

[ 0.7, 1.2],

[-2.2, 1.2],

[ 0.7, -1.2],

[-2.2, -1.2],

];

function drawScene() {

gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);

gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

gl.bindBuffer(gl.ARRAY_BUFFER, vertexPositionBuffer);

    gl.vertexAttribPointer(aVertexPosition, vertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);

var plotPositionBuffer = gl.createBuffer();

gl.bindBuffer(gl.ARRAY_BUFFER, plotPositionBuffer);

var cornerIx;

corners = [];

for (cornerIx in baseCorners) {

x = baseCorners[cornerIx][0];

y = baseCorners[cornerIx][1];

corners.push(x / zoom + centerOffsetX);

corners.push(y / zoom + centerOffsetY);

}

gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(corners), gl.STATIC_DRAW);

gl.vertexAttribPointer(aPlotPosition, 2, gl.FLOAT, false, 0, 0);

gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);

gl.deleteBuffer(plotPositionBuffer)

zoom *= 1.02;

document.getElementById("zoomOutput").value = zoom;

if (centerOffsetX != zoomCenterX) {

centerOffsetX += (zoomCenterX - centerOffsetX) / 20;

}

document.getElementById("centerOffsetXOutput").value = centerOffsetX;

if (centerOffsetY != zoomCenterY) {

centerOffsetY += (zoomCenterY - centerOffsetY) / 20;

}

document.getElementById("centerOffsetYOutput").value = centerOffsetY;

}

function resetZoom() {

zoom = 1.0;

zoomCenterX = parseFloat(document.getElementById("zoomCenterXInput").value);

zoomCenterY = parseFloat(document.getElementById("zoomCenterYInput").value);

}

function webGLStart() {

resetZoom();

var canvas = document.getElementById("example01-canvas");

initGL(canvas);

initShaders()

initBuffers();

gl.clearColor(0.0, 0.0, 0.0, 1.0);

setInterval(drawScene, 15);

}

</script>

</head>

  <canvas id="example01-canvas" style="border: none;" width="425" height="330"></canvas>

<h2>Inputs</h2>

<p>

Zoom target: <br />

X <input type="text" id="zoomCenterXInput" value="0.28693186889504513" />

Y <input type="text" id="zoomCenterYInput" value="0.014286693904085048" />

<p>

</form>

<h2>Current state (read-only)</h2>

<p>

Current center: <br />

  X <input type="text" id="centerOffsetXOutput" /> Y <input type="text" id="centerOffsetYOutput" />

<p>

Zoom: <input type="text" id="zoomOutput" />

</form>

<br/>

</body>

</html>

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