An Overview of WebGL

• We are skipping the next three chapters for now.
  • We may be back, but I just calculated that we have about 20 classes left this semester.
  • We will pick up parts of chapter 3 and 4 as we go along.
• We will not cover OpenGL
• We will cover some of WebGL
• These have a common base but they are not the same.
• OpenGL has gone through many generations
  • (Khronos group)
  • Version 1.x behaved much like the html canvas, but 3d.
  • Version 4.x is radically different.
• The Khronos Group
  • An open, non-profit consortium creating royalty-free interoperability standards for many different areas.
• There is a family of OpenGL products
  • (Khronos group)
  • OpenGL is the workstation library.
  • GL|ES is for phones (iOS and Android)
  • OpenMAX provides a cross-platform API for streaming media
  • OpenCL cross platform parallel programming language
  • WebGL what we are interestd in.
• WebGL
  • WebGL at Khronos.org
  • Cross platform open web standard low-level 3D graphics API based on OpenGL ES.
  • Used with the HTML5 canvas.
  • A free reference card is here
• WebGL consists of several parts
  • An API in javascript.
  • A shader programming language (GLSL)
• WebGL works as follows
  • (Packt )
  • A shader is a program that runs on the GPU
    • The vertex shader is executed once for each vertex.
    • The fragment shader is executed once for each fragment.
      • A fragment is a collection of values produced by the rasterizer. (reference.)
      • Multiple fragments can be produced per pixel depending on settings.
    • These are programmed in a c like language called GLSL
      • reference
  • A Vertex Buffer Object
    • Reference
    • Vertex data that has been stored on the GPU
    • These are the things you are going to draw.
  • When the drawing starts, vertexes, along with color, normals, ... are sent to the vertex shader as attributes.
  • Other data that is used to render the object is set by the CPU program as
    Uniforms
    • This is information such as transformation matrices.
  • The vertex shader can pass information to the fragment shader that is interpolated.
    • These are called varyings.
  • The fragment shader receives fragmets, the output of rasterization, and determines color values (among other things) for these fragments.
  • These are then sent to the framebuffer.