Hi,
I am trying to build a circle in webgl but I feel hopeless because I fail to build it. Can you help me to find out the mistake in my coding?
<script id=“shader-fs” type=“x-shader/x-fragment”>
#ifdef GL_ES
precision highp float;
#endif
varying vec4 vColor;
void main(void) {
gl_FragColor = vColor;
}
</script>
<script id=“shader-vs” type=“x-shader/x-vertex”>
attribute vec3 aVertexPosition;
attribute vec4 aVertexColor;
uniform mat4 uMVMatrix;
uniform mat4 uPMatrix;
varying vec4 vColor;
void main(void) {
gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);
vColor = aVertexColor;
}
</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(“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;
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);
shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);
shaderProgram.vertexColorAttribute = gl.getAttribLocation(shaderProgram, "aVertexColor");
gl.enableVertexAttribArray(shaderProgram.vertexColorAttribute);
shaderProgram.pMatrixUniform = gl.getUniformLocation(shaderProgram, "uPMatrix");
shaderProgram.mvMatrixUniform = gl.getUniformLocation(shaderProgram, "uMVMatrix");
}
var mvMatrix;
var mvMatrixStack = [];
function mvPushMatrix(m) {
if (m) {
mvMatrixStack.push(m.dup());
mvMatrix = m.dup();
} else {
mvMatrixStack.push(mvMatrix.dup());
}
}
function mvPopMatrix() {
if (mvMatrixStack.length == 0) {
throw “Invalid popMatrix!”;
}
mvMatrix = mvMatrixStack.pop();
return mvMatrix;
}
function loadIdentity() {
mvMatrix = Matrix.I(4);
}
function multMatrix(m) {
mvMatrix = mvMatrix.x(m);
}
function mvTranslate(v) {
var m = Matrix.Translation($V([v[0], v[1], v[2]])).ensure4x4();
multMatrix(m);
}
function createRotationMatrix(angle, v) {
var arad = angle * Math.PI / 180.0;
return Matrix.Rotation(arad, $V([v[0], v[1], v[2]])).ensure4x4();
}
function mvRotate(ang, v) {
var arad = ang * Math.PI / 180.0;
var m = Matrix.Rotation(arad, $V([v[0], v[1], v[2]])).ensure4x4();
multMatrix(m);
}
var pMatrix;
function perspective(fovy, aspect, znear, zfar) {
pMatrix = makePerspective(fovy, aspect, znear, zfar);
}
function setMatrixUniforms() {
gl.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, new Float32Array(pMatrix.flatten()));
gl.uniformMatrix4fv(shaderProgram.mvMatrixUniform, false, new Float32Array(mvMatrix.flatten()));
}
var z = -7.0;
var cubeVertexPositionBuffer;
var cubeVertexNormalBuffer;
var cubeVertexColorBuffer;
var cubeVertexIndexBuffer;
var unpackedColors;
var vectices;
var normalData;
function initBuffers() {
cubeVertexPositionBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);
var n = 4
var twoPi = 2.0 * 3.14159;
vertices = [0, 0, 0];
normalData = [0, 0, 1];
unpackedColors = [1, 0, 0, 1];
for (var j = 0; j <= n; j++) {
vertices = vertices.concat([Math.cos(j * twoPi / n), Math.sin(j * twoPi / n), 0.0]);
normalData = normalData.concat([0, 0, 1]);
unpackedColors = unpackedColors.concat([1, 0, 0, 1]);
}
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
cubeVertexPositionBuffer.itemSize = 3;
cubeVertexPositionBuffer.numItems = cubeVertexPositionBuffer.length / cubeVertexPositionBuffer.itemSize;
cubeVertexColorBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexColorBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(unpackedColors), gl.STATIC_DRAW);
cubeVertexColorBuffer.itemSize = 4;
cubeVertexColorBuffer.numItems = 6;
cubeVertexNormalBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexNormalBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(normalData), gl.STATIC_DRAW);
cubeVertexNormalBuffer.itemSize = 3;
cubeVertexNormalBuffer.numItems = cubeVertexNormalBuffer.length / cubeVertexNormalBuffer.itemSize;
cubeVertexIndexBuffer = gl.createBuffer();
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);
var cubeVertexIndices = [
0, 1, 2,
0, 2, 3,
0, 3, 4,
0, 4, 5,
0, 5, 6,
0, 6, 1
]
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(cubeVertexIndices), gl.STATIC_DRAW);
cubeVertexIndexBuffer.itemSize = 1;
cubeVertexIndexBuffer.numItems = 18;
}
function drawScene() {
gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
perspective(45, gl.viewportWidth / gl.viewportHeight, 0.1, 100.0);
loadIdentity();
mvTranslate([0, 0.0, z]);
multMatrix(rotationMatrix);
mvPushMatrix();
mvTranslate([-1, -1, 0]);
gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);
gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, cubeVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexColorBuffer);
gl.vertexAttribPointer(shaderProgram.vertexColorAttribute, cubeVertexColorBuffer.itemSize, gl.FLOAT, false, 0, 0);
gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexNormalBuffer);
gl.vertexAttribPointer(shaderProgram.vertexNormalAttribute, cubeVertexNormalBuffer.itemSize, gl.FLOAT, false, 0, 0);
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);
setMatrixUniforms();
gl.drawElements(gl.TRIANGLES, cubeVertexIndexBuffer.numItems, gl.UNSIGNED_SHORT, 0);
mvPopMatrix();
}
var mouseDown = false;
var lastMouseX = null;
var lastMouseY = null;
var rotationMatrix = Matrix.I(4);
function handleMouseDown(event) {
mouseDown = true;
lastMouseX = event.clientX;
lastMouseY = event.clientY;
}
function handleMouseUp(event) {
mouseDown = false;
}
function handleMouseMove(event) {
if (!mouseDown) {
return;
}
var newX = event.clientX;
var newY = event.clientY;
var deltaX = (newX - lastMouseX) / 2;
var deltaY = (newY - lastMouseY) / 2;
var newRotationMatrix = createRotationMatrix(deltaX, [0, 1, 0]);
newRotationMatrix = newRotationMatrix.x(createRotationMatrix(deltaY, [1, 0, 0]));
rotationMatrix = newRotationMatrix.x(rotationMatrix);
lastMouseX = newX
lastMouseY = newY;
}
function tick() {
drawScene();
}
function webGLStart() {
var canvas = document.getElementById(“lesson01-canvas”);
initGL(canvas);
initShaders();
initBuffers();
gl.clearColor(0.0, 0.0, 0.0, 1.0);
gl.clearDepth(1.0);
gl.enable(gl.DEPTH_TEST);
gl.depthFunc(gl.LEQUAL);
canvas.onmousedown = handleMouseDown;
document.onmouseup = handleMouseUp;
document.onmousemove = handleMouseMove;
setInterval(tick, 15);
}
Thanks your help.