SpaceBalls

Primarily a tech demo where I played around with pre-rendering 3D views and managing 3D transforms on the GBC.

Pursue and attack the enemy ship while dodging its laser fire.

Controls:

LEFT / RIGHT: Roll

UP / DOWN: Pitch

A: Fire lasers

B: Cycle Shield Configurations

B + UP/DOWN: Increase/decrease engine speed

There were a lot of technical challenges involved in getting this to run at 60Hz, so a lot of ideas are only partially developed, or left on the cutting room floor. For example, I just began working on the enemy AI this morning :P

Some points of interest:

• Pay attention to the location of the Sun when you are flying around. I chroma key the highlight color of the cockpit based on the Sun position, to give a lighting effect

•  While working on this project, I became convinced that there is a lot more possible in 3D with pre-rendering. Here, I am leveraging the rotational symmetry of spheres to reduce the amount of ROM usage. With clever design of model geometry and some restrictions, I think certain polygonal models are viable. 
  • The limiting factor is getting pixels into VRAM. I wanted to explore pre-fetching, since we should be able to predict adjacent views (or build a graph) with high-confidence but didn't have time to play with it. 
  • I messed with using hblank_copy for updating the render buffers within a single frame, but ultimately decided on a simple lazy-update scheme for moving tiles to VRAM, i.e. upload "x" tiles per frame, and flip buffers when the upload is complete.

•  Other tricks for reducing load are to design object motion and gameplay around the constraints of the system. 

• Setting this in space means that I can define the player as origin and cut out a transform, as well as approximating an arbitrarily large playfield. Also, I am dropping precision in the 3D calculations like crazy, with the expectation that player and enemy movement will dominate that precision loss.

• There is a lot of headroom left for general math improvements and optimizations. I didn't touch assembly for this project, or even use log tables for multiplication/division!

• Carefully choosing the for precision of each calculation is critical for balancing performance against numerical stability. I mostly just played it by feel because of time constraints, but there is a lot more benefit to be had.

Rendering 

Brief overview of the rendering procedure

• Offline, I generated evenly distributed views of the enemy ship for each scale, from 2px diameter to 32px.
• Select scale from view distance. Pre-calculated a table for this.
• From the set of tables for the selected render scale, select a view by normalizing the gaze vector and picking from the xyz values from the table.
  • object has rotational symmetry around the gaze vector, so can get away with 3DOF for this step
• Put the tile ids onto a work queue
• Each frame, load 4 tiles into the back buffer in VRAM
• When the tiles are completely loaded, swap buffers and display our new view

Glitches

• We've got 'em!