WebGL Quick Introduction
Dr Anton Gerdelan gerdela@scss.tcd.ie

About Me

  • Working on Knoholem smart buildings with Dave and Kris
  • Lectured in Karlskrona, Sweden. 3d, games, visualisation
  • Did most of PhD with GV2. Vehicle simulation, AI, graphics.

http://antongerdelan.net/3dmodelviewer/

Some Examples

"Deferred Irradiance Volumes" http://codeflow.org/webgl/deferred-irradiance-volumes/www/

Some Examples

HTML5 Canvas: "Where" to Draw

  • regular HTML page
  • can use HTML+jQuery user interface
  • can give dimensions

Start GL with JavaScript

Include some JS at end of web page

<script src="webgl-utils.js"></script> // Google's helper file
<script src="main.js"></script> // our JS file

Start GL Context and Hook Up to Canvas

// get canvas using DOM
var canvas = document.getElementById ("mycanvas");

// hook up WebGL to the canvas
gl = WebGLUtils.setupWebGL (canvas);

// make background red when cleared
gl.clearColor (0.5, 0.2, 0.0, 1.0);

Vertex Buffers: "What" to Draw

// create empty vertex buffer object in GL
var vbo_index = gl.createBuffer ();

// enable the VBO in GL state machine
gl.bindBuffer (gl.ARRAY_BUFFER, vbo_index);

// copy points into currently enabled buffer
gl.bufferData (gl.ARRAY_BUFFER, new Float32Array (points), gl.STATIC_DRAW);

Shader Programmes: "How" to Draw

Vertex Shader

attribute vec3 vp;
void main () {
  gl_Position = vec4 (vp, 1.0);
}

Fragment Shader

attribute vec3 vp;
precision mediump float;
void main () {
  gl_FragColor = vec4 (0.0, 0.0, 1.0, 1.0);
}

Render

// draw with shaders and vertex buffers
function render () {
  // wipe canvas to background colour
  gl.clear (gl.COLOR_BUFFER_BIT);
  
  // "use" shader for drawing all subsequent geometry
  gl.useProgram (shader_programme_index);
  // enable the first attribute in the vertex shader
  gl.enableVertexAttribArray (0);
  
  // set our vertex buffer as the one to be drawn
  gl.bindBuffer (gl.ARRAY_BUFFER, vbo_index);
  // map the buffer to shader attribute 0 (as enabled above)
  gl.vertexAttribPointer (0, 3, gl.FLOAT, false, 0, 0);
  
  // draw
  var number_of_points = 3;
  gl.drawArrays (gl.TRIANGLES, 0, number_of_points);
}
Result: index.html

Moving Things

JavaScript

  • get handle to "M" variable in shader gl.getUniformLocation()
  • "use" (enable) the shader programme gl.useProgram()
  • update value of variable in shader gl.uniformMatrix4fv()
  • Result: index.html

Vertex Shader Again

attribute vec3 vp;
uniform mat4 M;
void main () {
  gl_Position = M * vec4 (vp, 1.0);
}

GPU Parallelism

Summary

Advantages

Limitations

These slides/code

http://antongerdelan.net/teaching/webgl_intro/

Going Further

Quiz