fixatan2(3)

🎀 fixatan2 — the Allegro manual, bestie edition 🎀

okay so you found your way into the Allegro manual, and specifically into fixatan2(3) from the Allegro game programming library. pull up a chair, we're doing trig but make it fixed point. ✨

---

✨ NAME ✨

fixatan2 — it's the fixed point version of the libc atan2() routine, living its best life inside the Allegro game programming library. 🦋

---

🌸 SYNOPSIS 🌸

#include <allegro.h>

fixed fixatan2(fixed y, fixed x);

---

💖 DESCRIPTION 💖

So. This is a fixed point version of the libc atan2() routine. No floats invited to this party. 💅

What it does: it computes the arc tangent of y / x, BUT — and this is the part that eats — the signs of both arguments get used to figure out which quadrant the result should land in, and x is allowed to be zero (no div-by-zero meltdown, we love that for us 🫶).

It's genuinely useful for converting Cartesian coordinates into polar coordinates. iconic behaviour fr fr.

Example, and yes it's giving tutorial-core:

fixed result;

/* Sets `result' to binary angle 64. */
result = fixatan2(itofix(1), 0);
/* Sets `result' to binary angle -109. */
result = fixatan2(itofix(-1), itofix(-2));
/* Fails the assert. */
result = fixatan2(0, 0);
ASSERT(!errno);

⚠️ not me pointing at that third call — fixatan2(0, 0) sets errno, so that ASSERT(!errno) is going to fail. it says so right there in the comment. periodt. 💀

---

🌈 RETURN VALUE 🌈

It returns the arc tangent of y / x as a fixed point binary format angle, ranging from -128 to 128. 📐

But bestie, listen — if both x and y are zero, it returns zero and sets errno to EDOM. that's the failure vibe check. no cap.

---

👑 SEE ALSO 👑

• exlights(3) — go look at it 💜
• exspline(3) — also go look at it 💜

---

and that's the whole page, bestie!! you ate. 🍓💅

Allegro, version 4.4.3 — signed off with love from fixatan2(3), mwah 🎀✨🦋