Ciao a tutti,
ho un rettangolo fatto in webgl e un bottone che deve cambiare il suo colore.
Come la scrivo la funzione che lo cambia???
Questo è il codice del rettangolo:
<html>
<head>
<script id="shader-fs" type="x-shader/x-fragment">
#ifdef GL_ES
precision highp float;
#endif

void main(void) {
gl_FragColor = vec4(1.0,1.0,1.0,1.0);
}
</script>

<script id="shader-vs" type="x-shader/x-vertex">
attribute vec3 aVertexPosition;

uniform mat4 uMVMatrix;
uniform mat4 uPMatrix;

void main(void) {
gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);

}
</script>

<script type="text/javascript" src="Sylvester.js"></script>
<script type="text/javascript" src="glUtils.js"></script>
<script type="text/javascript" src="MatriUtilityFunc.js"></script>


<script type="text/javascript">

var gl;
function initGL(canvas) {
try {
gl = canvas.getContext("experimental-webgl");
gl.viewportWidth = canvas.width;
gl.viewportHeight = canvas.height;
} catch(e) {
}
if (!gl) {
alert("Impossibile Inizializzare WebGL.Devi avere un Browser con webgl abilitato per vedere qualcosa!");
}

gl.clearColor(0.0, 0.0, 0.0, 1.0);
gl.clearDepth(1.0);
gl.enable(gl.DEPTH_TEST);
gl.depthFunc(gl.LEQUAL);

}

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;

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("Non posso inizializzare gli shader");
}


gl.useProgram(shaderProgram);
shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
gl.enableVertexAttribArray(shaderProgram.vertexPos itionAttribute);
shaderProgram.pMatrixUniform = gl.getUniformLocation(shaderProgram, "uPMatrix");
shaderProgram.mvMatrixUniform = gl.getUniformLocation(shaderProgram, "uMVMatrix");
}

var squareVertexPositionBuffer;
function initBuffers() {
squareVertexPositionBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);

vertices = [

1.0, 0.05, 0.0,
-1.0, 0.05, 0.0,
1.0, -0.05, 0.0,
-1.0, -0.05, 0.0

];

gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
squareVertexPositionBuffer.itemSize = 3;
squareVertexPositionBuffer.numItems = 4;


}



function drawScene() {
gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight); //1
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT); //2
perspective(45, gl.viewportWidth / gl.viewportHeight, 0.1, 100.0); //3
loadIdentity(); //4
mvTranslate([0.0, 0.0, -3.0]); //5
gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer); //6
gl.vertexAttribPointer(shaderProgram.vertexPositio nAttribute, squareVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
setMatrixUniforms(); //8
gl.drawArrays(gl.TRIANGLE_STRIP, 0, squareVertexPositionBuffer.numItems); //9

}

function Start() {
var canvas = document.getElementById("Mycanvas");
initGL(canvas);
initShaders();
initBuffers();
setInterval(tick, 15);
}


function tick()
{
drawScene();
}
</script>



</head>

<body onload="setTimeout(Start,1000);">
<canvas id="Mycanvas" width="800" height="400"></canvas>


<input type="button" value="Cambia colore" onclick" ">


</body>
</html>