Yeti3D GBA

Yeti3D
General
Author	Derek Evans
Type	Game engine
Version	2 Demo
License	Mixed
Last Updated	2003/08/13
Links
Download
Website
Source

This is the second public release of the Yeti 3D Engine. The Yeti engine is a fully featured 3d engine designed for low cost portable devices, namely the GameBoy Advanced, mobile phones and Palm units. It should therefore run on just about anything.

User guide

These are design notes for the Yeti engine. Other engines use very different algorithms.

• The current viewport is 120x80 pixels, 15bit.
• All textures are 64x64 8bit.
• Textures are converted to 15bit via a pre-calculated lighting LUT.
• Polygons can be any convex shape. Only squares are currently used.
• Each vertex is described as X, Y, Z, U, V and brightness.
• The renderer uses 24:8 fixed point maths.
• Polygons are clipped in 3D space using 45 degree planes. Distance to plane calculations therefore use only additions and subtractions.
• Polygon edges are clipped using one divide and 6 multiplies.
• 4 clipping planes are used. No front plane is required. No back plane is used.
• No per-span clipping is used. Fixed point errors are hidden offscreen.
• Ray-casting is used to build a visablity list and valid polygon rendering order.
• Models are merged into the VIS without sorting.
• No Z-buffers are used. Rendering is back-to-front (painters algorithm).
• The is an acceptable level of overdraw. Complete polygons are culled. Polygon edges are drawn faster than using a per span clipper.
• Lighting is pre-calculated on startup. Lighting can be moved at runtime.
• Lighting is expanded per vertex and interpolated along polygon edges.
• A reciprocal table is used to eliminate all divides from the DDA texture mapper.
• The affine texture loop is unrolled and renders blocks of 32 pixels.

Media

Yeti 3D GBA Engine Tech DEMO (Jaroslav Dolejší)

External links

• Author's website - http://theteahouse.com.au/gba/ (archived)