Texture Mapping

• Definition
  A scheme for altering on a sample-by-sample basis (e.g., per-pixel or per-fragment) one or more attributes of – and hence the color displayed for – a primitive.
• Implementation approaches:
  • Purely procedural (recall twoTriangles_V2 in Sample Program Set 1)
  • Image-Based Texture Mapping in which image data is used
• In interactive APIs like OpenGL, texture mapping is typically performed in the fragment shader.

A wall that is 8 x 15 feet

The actual texture image

• In the following, we will focus exclusively on Image-Based Texture Mapping and, in particular, on two key aspects:
  • Color Generation Mode which relates to the specifics of whether and how a texture is used
  • Mapping which relates to how "texture space" relates to "MC space"

    While the basics of the "mapping" part are straightforward, acceptable results require that the mapping produce realistic results. This requires attention be paid to what the size of a texture should be in relation to the size of the object on which it is mapped. This is very important!

• Example code extracts
  • CPU ModelView subclass
    • SceneElement.c++
  • Portions of the vertex shader
  • Some fragment shader pseudocode
• Mipmapping
• glTexParameter*
  • This routine allows the OpenGL programmer to specify several important aspects related to how the built-in GLSL function texture works.
  • Common glTexParameter calls

Advanced Texture Mapping

• Multitexturing allows multiple textures to be used on a single polygon.
• Cube maps are used to assign textures to the six faces of a cube. While this can be used simply for that purpose, cube maps are most commonly used to implement a technique known as "environment mapping".