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CSS Base

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HTML Settings

Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

              <canvas id="main" width="500" height="400" />

 * Part 2 Challenges:
 * - Change the gradient to be white
 *   to black, left-to-right only
 * - Make a checkerboard pattern (hint: https://www.opengl.org/sdk/docs/man/html/mod.xhtml)
 * - Make a checkerboard pattern without using conditions! (hint: https://www.opengl.org/sdk/docs/man/html/step.xhtml)

var canvas = document.getElementById("main");
var gl = canvas.getContext('webgl');

 * Shaders

// Utility to fail loudly on shader compilation failure
function compileShader(shaderSource, shaderType) {
    var shader = gl.createShader(shaderType);
    gl.shaderSource(shader, shaderSource);

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        throw "Shader compile failed with: " + gl.getShaderInfoLog(shader);

    return shader;

var vertexShader = compileShader('\n\
attribute vec2 position;\n\
void main() {\n\
    // position specifies only x and y.\n\
    // We set z to be 0.0, and w to be 1.0\n\
    gl_Position = vec4(position, 0.0, 1.0);\n\

var fragmentShader = compileShader('\n\
void main(){\n\
    gl_FragColor = vec4(gl_FragCoord.x/500.0, \n\
                        gl_FragCoord.y/400.0, \n\
                        0.0, 1.0);\n\

var program = gl.createProgram();
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);

 * Geometry setup

// Set up 4 vertices, which we'll draw as a rectangle
// via 2 triangles
//   A---C
//   |  /|
//   | / |
//   |/  |
//   B---D
// We order them like so, so that when we draw with
// gl.TRIANGLE_STRIP, we draw triangle ABC and BCD.
var vertexData = new Float32Array([
    -1.0,  1.0, // top left
    -1.0, -1.0, // bottom left
     1.0,  1.0, // top right
     1.0, -1.0, // bottom right
var vertexDataBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexDataBuffer);
gl.bufferData(gl.ARRAY_BUFFER, vertexData, gl.STATIC_DRAW);

 * Attribute setup

// Utility to complain loudly if we fail to find the attribute

function getAttribLocation(program, name) {
    var attributeLocation = gl.getAttribLocation(program, name);
    if (attributeLocation === -1) {
        throw 'Can not find attribute ' + name + '.';
    return attributeLocation;

// To make the geometry information available in the shader as attributes, we
// need to tell WebGL what the layout of our data in the vertex buffer is.
var positionHandle = getAttribLocation(program, 'position');
                       2, // position is a vec2
                       gl.FLOAT, // each component is a float
                       gl.FALSE, // don't normalize values
                       2 * 4, // two 4 byte float components per vertex
                       0 // offset into each span of vertex data

 * Draw

// Render the 4 vertices specified above (starting at index 0)
// in TRIANGLE_STRIP mode.
gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);

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