square.html
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<html>
<head>
<title>First very simple WebGL example...</title>
<script src="./gl-matrix-min.js" type="text/javascript"></script>
<script type="text/javascript">
var projectionMatrix, modelViewMatrix;
var shaderProgram, shaderVertexPositionAttribute;
var shaderProjectionMatrixUniform, shaderModelViewMatrixUniform;
function initWebGL(canvas) {
var gl = null;
var msg = "Your browser does not support WebGL, " +
"or it is not enabled by default.";
try {
gl = canvas.getContext("experimental-webgl");
}
catch (e) {
msg = "Error creating WebGL Context!: " + e.toString();
}
if (!gl) {
alert(msg);
throw new Error(msg);
}
return gl;
}
function initViewport(gl, canvas) {
gl.viewport(0, 0, canvas.width, canvas.height);
}
// Create the vertex data for a square to be drawn
function createSquare(gl) {
var vertexBuffer;
vertexBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
var verts = [
.5, .5, 0.0,
-.5, .5, 0.0,
.5, -.5, 0.0,
-.5, -.5, 0.0
];
gl.bufferData(
gl.ARRAY_BUFFER,
new Float32Array(verts),
gl.STATIC_DRAW);
var square = {
buffer:vertexBuffer,
vertSize:3,
nVerts:4,
primtype:gl.TRIANGLE_STRIP};
return square;
}
function initMatrices(canvas) {
// Create a model view matrix with camera at 0, 0, −3.333
modelViewMatrix = mat4.create();
mat4.translate(
modelViewMatrix, modelViewMatrix, [0, 0, -3.333]);
// Create a project matrix with 45 degree field of view
projectionMatrix = mat4.create();
mat4.perspective(projectionMatrix, Math.PI / 4,
canvas.width / canvas.height, 1, 10000);
}
function createShader(gl, id, type) {
var shader;
var str = document.getElementById(id).text;
if (type == "fragment") {
shader = gl.createShader(gl.FRAGMENT_SHADER);
} else if (type == "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;
}
function initShader(gl, vertex, fragment) {
// load and compile the fragment and vertex shader
var fragmentShader = createShader(gl, fragment, "fragment");
var vertexShader = createShader(gl, vertex, "vertex");
// link them together into a new program
shaderProgram = gl.createProgram();
gl.attachShader(shaderProgram, vertexShader);
gl.attachShader(shaderProgram, fragmentShader);
gl.linkProgram(shaderProgram);
// get pointers to the shader params
shaderVertexPositionAttribute = gl.getAttribLocation(
shaderProgram, "vertexPos");
gl.enableVertexAttribArray(shaderVertexPositionAttribute);
shaderProjectionMatrixUniform = gl.getUniformLocation(
shaderProgram, "projectionMatrix");
shaderModelViewMatrixUniform = gl.getUniformLocation(
shaderProgram, "modelViewMatrix");
if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
alert("Could not initialise shaders");
}
}
function draw(gl, obj) {
// clear the background (with black)
gl.clearColor(0.0, 0.0, 0.0, 1.0);
gl.clear(gl.COLOR_BUFFER_BIT);
// set the vertex buffer to be drawn
gl.bindBuffer(gl.ARRAY_BUFFER, obj.buffer);
// set the shader to use
gl.useProgram(shaderProgram);
// connect up the shader parameters: vertex position and
// projection/model matrices
gl.vertexAttribPointer(
shaderVertexPositionAttribute,
obj.vertSize,
gl.FLOAT, false, 0, 0);
gl.uniformMatrix4fv(
shaderProjectionMatrixUniform,
false, projectionMatrix);
gl.uniformMatrix4fv(
shaderModelViewMatrixUniform, false, modelViewMatrix);
// draw the object
gl.drawArrays(obj.primtype, 0, obj.nVerts);
}
function startGl() {
// Get A WebGL context
var canvas = document.getElementById("square");
var gl = initWebGL(canvas);
var obj = createSquare(gl);
initViewport(gl, canvas);
initMatrices(canvas);
initShader(
gl,
"square-vertex-shader",
"square-fragment-shader");
draw(gl, obj);
}
</script>
<script id="square-vertex-shader" type="x-shader/x-vertex">
attribute vec3 vertexPos;
uniform mat4 modelViewMatrix;
uniform mat4 projectionMatrix;
void main(void) {
// Return the transformed and projected vertex value
gl_Position =
projectionMatrix * modelViewMatrix * vec4(vertexPos, 1.0);
}
</script>
<script id="square-fragment-shader" type="x-shader/x-fragment">
void main(void) {
// Return the pixel color: always output white
gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
}
</script>
</head>
<body onLoad="startGl()">
<canvas id="square" width="200" height="200"></canvas>
</body>
</html>
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