Interesting blog

I found an interesting blog over at http://benryves.com. It belongs to a guy that seems to share my passion for low end systems. He's working on a 2.5D engine for the TI-83 and has a bunch of different hardware and software projects.

GBA 3D Rendering

I've finally put all the pieces together, and it turned out pretty good imo. The video shows a rotating torus with a rotating directional light. I'd love to do point lights, but the inverse square root needed for normalization is extremely expensive in terms of CPU time needed.

Fixed point division

Found an interesting article about fast fixed point division and multiplication on ARM processors over at Henry Thomas consulting. Originally I claimed that it didn't work for the GBA, but that was a lie. Some minor tweaks and now it runs like a charm. Fixed point division used to be a major bottleneck in my attempt at 3D rendering on the GBA, and now it's not a problem at all.

Refreshing my memory (3d math)

So.. it's been a while since the last time I did all the 3D calculations myself. Nowadays I just use libraries since every decent graphics API have it build in, but that isn't the case for the GBA. I started implementing the functions needed for matrix transformations and quickly concluded with that I suspected before starting: a naive implementation will be way too slow. You still need the background information to start optimizing though. The following is a good starting point at least: Egon Rath's Notes: Basic 3D Math: Matrices.

GBA: Useful links

Here are some useful links when developing for the GBA:

GBA

• GBATEK - Gameboy Advance / Nintendo DS - Technical Info
• gbadev.org
• devKitPro
• TONC Tutorials
• Gamedev.net - GBA Development From the Ground Up
• Gamasutra - Gameboy Advance Resource Management
• Maxmod - Music And Sound Solution
• Sound on the GBA
• Realtime 3D on the GBA
• Gameboy Advance Resources
• Dev'rs GBA Dev FAQs

ARM

• The ARM instruction set
• GBA ASM Tutorial
• ARM Assembler Intro
• Coranac: Bit-tricks and other nifty little snippets

Math

• Another fast fixed-point sine approximation
• ARM Square Root
• Fixed Point Square Root (pdf)
• By a Desolate Stream - Square Root
• ARM code inverse square root routines

GBA: Place functions/variables in iwram

Placing functions and variables in iwram will *seriously* speed up your program. You only have limited amounts on the other hand (32K). I made the following defines based on The Dev'rs GBA Dev FAQs.

Defines:

#define IWRAM_FUNCTION __attribute__((section (".iwram"), long_call))
#define IWRAM_VARIABLE __attribute__((section (".iwram")))

Usage:

const int somearray[] IWRAM_VARIABLE = { ... }
void IWRAM_FUNCTION SomeFunction( ... ) { ... }

I figured out that there's some more info on this over at tonc after I posted.

One of my many 2d sprite projects

This is a test of a 2d engine with custom physics I worked on a while ago. Art credits goes to Zelda :)