Screenshot
Live demonstration of the four math primitives a 2D action game leans on the most: sqrt16 (pixel distance), atan2_8 (8-bit angle to a target), and the fixCos / fixSin LUTs (project a velocity vector along that angle). Everything updates live as the user moves the target with the D-pad — the numbers on screen are real arithmetic, not pre-baked.
The player diamond stays anchored at the screen centre; the X follows the D-pad. Each frame the example recomputes dx/dy from the two positions, calls sqrt16(dx² + dy²) for the pixel distance, calls atan2_8(dy, dx) for the 8-bit angle, then calls fixCos and fixSin on that angle to read back the unit direction vector.
SNES Concepts
- <snes/math.h> square-root and atan2 (chantier B6, 2026-05-09):
- sqrt16(n) → integer floor of √n, range 0–255
- atan2_8(dy, dx) → 8-bit angle in the same convention as the fixSin / fixCos LUTs (0 = +X, 64 = +Y, 128 = −X, 192 = −Y)
- LUT chaining — feed the atan2_8 output back into the trig LUT to recover a unit direction vector that points from player to target. This is the canonical pattern for projectile aiming, pursuit AI, and any "rotate sprite to face X" code.
- Mode 0 + sprite overlay — BG1 hosts the text via the text module; the player and target are 8×8 OBJ sprites on the OBJ layer so they don't disturb the text display. Sprite tiles are placed at VRAM $4000 to keep $0000 free for the text font.
What to Observe
The live readout panel updates every frame:
- DX / DY — signed distances from player to target
- DIST — sqrt16(dx² + dy²) in pixels (0–255)
- ANGLE — 8-bit angle from the player to the target (hex), with the equivalent in degrees in parentheses (≈ angle × 360 / 256)
- COS / SIN — 8.8 fixed-point components of the unit direction vector. Their values match the angle: at ANGLE = 0x40 (90°, target straight south on a SNES screen) you see COS = 0x0000 and SIN = 0x0100.
Move the X around with the D-pad and watch the entire panel react in real time.
How to Build
make -C examples/basics/aim_target
The ROM lands at examples/basics/aim_target/aim_target.sfc.
Modules Used
console, sprite, dma, background, text, input, gameloop, math.
See also
1.16.1