3D Fundamentals Tutorial 7

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Textures. Put purdy pictures onto your triangles. Lot of interpolation and stuff.


The tutorial video is on YouTube here.

  • What is texture mapping and why do we want it? 0:14
  • Mapping a picture onto a geometry (triangles)
  • Basically, to create real life imagery with high fidelity
  • How to approach texture mapping 2:45
  • How NOT to do it: sccaling and rotating points of a sprite
  • Right way: Generate a mapping of vertices of our geometry to points in our texture
  • This requires:
- Transform the vertices to screen space
- Rasterize (using scanlines)
- Interpolate from the geometry's screen coordinates (x,y) to coordinates of the texture (u,v)
- Use the texture's color at (u,v) to draw the pixel on the screen at (x,y)
  • Interpolating between three vertices 5:33
  • Pre-stepping 7:20
  • This is done based on the positions of the center of the starting pixel & the scanline
  • Implementing these concepts into code 8:42
  • The TexVertex class
  • Incorporating data & methods in Cube.h
  • Implementing DrawTriangleTex(...) triangle drawing with textures in Graphics.h and Graphics.cpp 10:55
  • Texture mapping code 13:50
  • Texture coordinates pre-stepping 15:23
  • The scanline loop 17:26
  • The PutPixel call with tex.GetPixel(...) 17:26
- We define the texture in normalized space / normalized coordinates, this has clear advantages
- We apply texture clamping to make the code robust
  • Demonstration on screen 23:00
  • We observe limitations. Main one: because we map base vertices, we cannot texturize all surfaces
  • Improving the interpolation algorithm 26:32
  • Smarter interpolation: no slope calculations, unifying screen & texture coordinate interpolation
  • Introduction of the TexVertex class
  • Consolidating flat top & flat bottom triangle drawing routines 31:15
  • Put common routingen in a single function, create wrappers for distinct parts for flat top/bottom
  • This ceates cleaner code (no duplication), important for maintainability
  • Adding features: texture clamping and texture wrapping 33:15
  • For clamping, we use std::max
  • For wrapping, we use std::fmod (floating point modulus)
  • Fixing texture mapping of top & bottom: unfolding the geometry of the cube 36:00
  • We "break the weld" (/sharing) of vertices of the cube's different faces
  • The number of vertices required depends on the level of flexibility/independence: we can move from 8->14->24 vertices
  • Implementing unfolding & full surface mapping in the code 38:40
  • Creating a skin for a cube 39:56
  • Advantages of using normalized texture coordinates 41:30
  • Improving texture image quality: bilinear filtering, (isotropic) mip mapping, normal mapping 43:25
  • Recap: you are now master of texture mapping, reverse lookup & interpolation 45:30


The GitHub repository for the tutorial code is here.

See also