So, my goal is to be able to render a 3-D sphere(sorry for the redundancy) by using recursive subdivision, here is the image the textbook gives as an example:
Sphere approximations using subdivision
The textbook is not very helpful overall, with anything really, I did attempt to ask my professor for help with this and his response was “Google it”. So I did, and I managed to piece together what I thought would work, but sadly I cannot actually get anything to render, and I am completely lost as to why. I don’t know if I have just been staring at this for so long I am missing something completely obvious or what, but I would really appreciate any help anyone could offer.
<!doctype html>
<html>
<body>
<canvas width = "600" height = "600" style="border:1px solid #000000" id="sphere_canvas"></canvas>
<script>
var gl1;
function initgl1(canvas) {
try {
gl1 = canvas.getContext("experimental--webgl1");
gl1.viewportWidth = canvas.width;
gl1.viewportHeight = canvas.height;
} catch (e) {
}
if (!gl1) {
alert("we Couldnt initialise Webgl1 , sorry :-(");
}
}
function getShader(gl1, 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 = gl1.createShader(gl1.FRAGMENT_SHADER);
} else if (shaderScript.type == "x- shader/x-vertex") {
shader = gl1.createShader(gl1.VERTEX_SHADER);
} else {
return null;
}
gl1.shaderSource(shader, str);
gl1.compileShader(shader);
if (!gl1.getShaderParameter(shader, gl1.COMPILE_STATUS)) {
alert(gl1.getShaderInfoLog(shader));
return null;
}
return shader;
}
var shaderProgram;
function initShaders() {
var fragmentShader = getShader(gl1, "shader-fs");
var vertexShader = getShader(gl1, "shader-vs");
shaderProgram = gl1.createProgram();
gl1.attachShader(shaderProgram, vertexShader);
gl1.attachShader(shaderProgram, fragmentShader);
gl1.linkProgram(shaderProgram);
if (!gl1.getProgramParameter(shaderProgram, gl1.LINK_STATUS)) {
alert("Could not initialise shaders");
}
gl1.useProgram(shaderProgram);
shaderProgram.vertexPositionAttribute = gl1.getAttribLocation(shaderProgram, "aVertexPosition");
gl1.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);
shaderProgram.vertexColorAttribute = gl1.getAttribLocation(shaderProgram, "aVertexColor");
gl1.enableVertexAttribArray(shaderProgram.vertexColorAttribute);
shaderProgram.pMatrixUniform = gl1.getUniformLocation(shaderProgram, "uPMatrix");
shaderProgram.mvMatrixUniform = gl1.getUniformLocation(shaderProgram, "uMVMatrix");
}
var mvMatrix = mat4.create();
var mvMatrixStack = [];
var pMatrix = mat4.create();
function mvPushMatrix() {
var copy = mat4.create();
mat4.copy(copy, mvMatrix);
mvMatrixStack.push(copy);
}
function mvPopMatrix() {
if (mvMatrixStack.length == 0) {
throw "Invalid popMatrix!";
}
mvMatrix = mvMatrixStack.pop();
}
function setMatrixUniforms() {
gl1.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, pMatrix);
gl1.uniformMatrix4fv(shaderProgram.mvMatrixUniform, false, mvMatrix);
}
function degToRad(degrees) {
return degrees * Math.PI / 180;
}
var sphereVertexPositionBuffer;
var sphereVertexColorBuffer;
var sphereVertexIndexBuffer;
function initBuffers() {
var latitudeBands = 10;
var longitudeBands = 10;
var radius = 2;
sphereVertexPositionBuffer = gl1.createBuffer();
gl1.bindBuffer(gl1.ARRAY_BUFFER, sphereVertexPositionBuffer);
sphereVertexColorBuffer = gl1.createBuffer();
gl1.bindBuffer(gl1.ARRAY_BUFFER, sphereVertexColorBuffer);
sphereVertexIndexBuffer = gl1.createBuffer();
gl1.bindBuffer(gl1.ELEMENT_ARRAY_BUFFER, sphereVertexIndexBuffer);
var vertexPositionData = [];
var colors = [];
var indexData = [];
for (var latNumber=0; latNumber < latitudeBands; latNumber++) {
var theta = latNumber * Math.PI / latitudeBands;
var sinTheta = Math.sin(theta);
var cosTheta = Math.cos(theta);
for (var longNumber=0; longNumber < longitudeBands; longNumber++) {
var phi = longNumber * 2 * Math.PI / longitudeBands;
var sinPhi = Math.sin(phi);
var cosPhi = Math.cos(phi);
var x = cosPhi * sinTheta;
var y = cosTheta;
var z = sinPhi * sinTheta;
colors = [[1.0, 1.0, 0.3, 1.0]];
vertexPositionData.push(radius * x);
vertexPositionData.push(radius * y);
vertexPositionData.push(radius * z);
var first = (latNumber * (longitudeBands + 1)) + longNumber;
var second = first + longitudeBands + 1;
indexData.push(first);
indexData.push(second);
indexData.push(first + 1);
indexData.push(second);
indexData.push(second + 1);
indexData.push(first + 1);
}
}
var unpackedColors = [];
for (var i in colors) {
var color = colors[i];
for (var j=0; j < 4; j++) {
unpackedColors = unpackedColors.concat(color);
}
}
gl1.bufferData(gl1.ARRAY_BUFFER, new Float32Array(vertexPositionData), gl1.STATIC_DRAW);
sphereVertexPositionBuffer.itemSize = 3;
sphereVertexPositionBuffer.numItems = vertexPositionData.length / 3;
gl1.bufferData(gl1.ARRAY_BUFFER, new Float32Array(unpackedColors), gl1.STATIC_DRAW);
sphereVertexColorBuffer.itemSize = 4;
sphereVertexColorBuffer.numItems = unpackedColors.length / 4;
gl1.bufferData(gl1.ELEMENT_ARRAY_BUFFER, new Uint16Array(indexData), gl1.STATIC_DRAW);
sphereVertexIndexBuffer.itemSize = 1;
sphereVertexIndexBuffer.numItems = indexData.length;
}
var rSphere = 0;
function drawScene() {
gl1.viewport(0, 0, gl1.viewportWidth, gl1.viewportHeight);
gl1.clear(gl1.COLOR_BUFFER_BIT | gl1.DEPTH_BUFFER_BIT);
mat4.perspective(pMatrix, 60, gl1.viewportWidth / gl1.viewportHeight, 0.1, 100.0);
mat4.identity(mvMatrix);
mat4.translate(mvMatrix, mvMatrix, [0.0, 0.0, -5.0]);
mvPushMatrix();
mat4.rotate(mvMatrix, mvMatrix, degToRad(rSphere), [1, 1, 1]);
gl1.bindBuffer(gl1.ARRAY_BUFFER, sphereVertexPositionBuffer);
gl1.vertexAttribPointer(shaderProgram.vertexPositionAttribute, sphereVertexPositionBuffer.itemSize, gl1.FLOAT, false, 0, 0);
gl1.bindBuffer(gl1.ARRAY_BUFFER, sphereVertexColorBuffer);
gl1.vertexAttribPointer(shaderProgram.vertexColorAttribute, sphereVertexColorBuffer.itemSize, gl1.FLOAT, false, 0, 0);
gl1.bindBuffer(gl1.ELEMENT_ARRAY_BUFFER, sphereVertexIndexBuffer);
setMatrixUniforms();
gl1.drawElements(gl1.TRIANgl1ES, sphereVertexIndexBuffer.numItems, gl1.UNSIGNED_SHORT, 0);
mvPopMatrix();
}
var lastTime = 0;
function animate() {
var timeNow = new Date().getTime();
if (lastTime != 0) {
var elapsed = timeNow - lastTime;
rSphere -= (75 * elapsed) / 1000.0;
}
lastTime = timeNow;
}
function tick() {
requestAnimFrame(tick);
drawScene();
animate();
}
function webgl1Start() {
var canvas = document.getElementById("sphere_canvas");
initgl1(canvas);
initShaders()
initBuffers();
gl1.clearColor(0.0, 0.0, 0.1, 1.0);
gl1.enable(gl1.DEPTH_TEST);
tick();
}
</script>
</body>
</html>
