fix32_orbit

Screenshot

A single 8×8 sprite orbits the screen centre, driven entirely by the lib's 16.16 fixed-point API (<snes/fixed32.h>). It's the simplest possible fixed32 fixture: one trig-driven motion equation, no input, no game logic — just the radius × cos / radius × sin pattern that every 2D game uses for orbits, aiming, and parallax-around-a-point.

Each frame the example advances a 16.16 angle accumulator, reads fix32Cos / fix32Sin for that angle, scales them by the radius with fix32Mul, and projects the result to integer screen coordinates centred at (128, 96).

SNES Concepts

• fixed32 (s32 16.16) — a 16.16 accumulator keeps the angle smooth across hundreds of frames without the rounding drift an 8.8 type would accumulate.
• fix32Sin / fix32Cos — the trig LUTs lifted to 16.16 (≈25 cycles each), enough fractional precision for sub-pixel animation.
• fix32Mul(radius, fix32Cos(angle)) — the canonical trig-driven motion term, reused in aim_target, likemario, and breakout.
• Minimal sprite setup — one 4bpp tile DMAed to VRAM $4000, a two-colour palette at the sprite CGRAM base, OBJSEL pointed at the tile base, then a single oamSet per frame.

What to Observe

The white dot traces a smooth circle around the screen centre — about one full revolution every ~3.9 s at 60 Hz (g_omega = FIX32(1), one LUT step per frame). The motion is continuous and sub-pixel-smooth because the angle lives in 16.16, not in screen pixels. The orbit state is exposed as globals (g_angle, g_radius, g_sx, g_sy) for easy inspection while debugging.

How to Build

make -C examples/basics/fix32_orbit

The ROM lands at examples/basics/fix32_orbit/fix32_orbit.sfc.

Modules Used

console, sprite, dma, background, fixed32, math.

See also

• docs/tutorials/math.md — the fixed-point math tutorial.
• lib/include/snes/fixed32.h — Doxygen reference for the 16.16 API.
• examples/basics/aim_target — the same trig primitives composed into live distance/angle/aiming readouts.