Topics for the Week of Nov 3, 2008
CS 445: Computer Graphics

• Labs - Tues
  • Look at a Lab 4: Lighting, Normals and Color Ramps.
  • Begin Lab 5: A Walk Through a Museum.
• Textures -
  • Where do they fall in the pipeline
  • Scanline Fill Algorithm
  • Anti-aliasing
  • Mapping Textures and texture coordinates in OpenGL
  • Generating Textures: Procedural Textures, Generating Noise
  • Texturing Process in OpenGL
    1. Read in your images and, for Java, store in ByteBuffer. For OpenGL 2.0 and greater, the image doesn't have to have sizes that are powers of 2.
    2. Obtain unused texture identifiers - glGenTextures
    3. Set current texture ID using glBindTexture
    4. Set texture object state parameters - glTexParameter - e.g. how textures are filtered when texels are different size from pixels.
    5. Set texture environment parameters - glTexEnvi - e.g. how texture interacts with lighting
    6. Load into texture memory - glTextImage2D or glBuild2DMipmaps
    7. Before rendering - set the current texture using glBindTexture
    8. Before rendering - enable texturing glEnable(GL.GL_TEXTURE_2D)
    9. Render - Send geometry to OpenGL making sure to set texture coordinates
       • Done manually with glTextCoord
       • Can be done automatically - glEnable(GL_TEXTURE_GEN_S) etc Must specify how,e.g. eye_linear, sphere_map etc
    10. Disable texturing if subsequent rendering does not use texturing - glDisable(GL.GL_TEXTURE_2D)
  • Look at openGL examples
    • TextureCube (code on enfuzion). It shows
      • How to load an image into Java.
      • How to procedurally generate an image texture.
      • How to convert an image into a ByteBuffer.
      • How to use multiple textures.
      • How to assign texture coordinates to geometry.
    • TextureParamExample - Orthographic view of square. It shows
      • How to load an image into Java.
      • How to convert an image into a ByteBuffer.
      • How to use multiple textures.
      • How to assign texture coordinates to geometry.
      • The effect of changing the mode (decal cs modulate). This affects the interaction of texturing and lighting.
      • The effect of changing the wrap (clamp vs repeat)
    • EarthTexture - Displays the planets from our solar system. It shows
      • How to use multiple textures.
    • AlgebraicWithTexture - Displays the algebraic surface (Steiner). It shows
      • How to generate texture coordinates to a non-rectangular surface.
    • SeaShellTexture - Displays the shell-like or horn-like algebraic surface. It shows
      • The effect of changing the texture mode, e.g. gl_decal, gl_modulate, etc so that texturing, environment effects, and lighting can all interact.

  • Environment Mapping - Cube maps in OpenGL, or Reflection Mapping, e.g. teapot