arc(3)

📦 version 4.4.3.1, in fedora 43, fedora 44

💫 arc(3) 💫

okay bestie, welcome to the Allegro manual — today's main character is arc, and she draws circles. well, parts of circles. iconic behaviour, honestly.

🌸 NAME 🌸

arc — draws a circular arc. it's giving Allegro game programming library, and it's giving geometry. 🎀

✨ SYNOPSIS ✨

#include <allegro.h>

void arc(BITMAP *bmp, int x, y, fixed ang1, ang2, int r, int color);

🦋 DESCRIPTION 🦋

so here's the vibe: arc draws a circular arc with centre x, y and radius r, going in an anticlockwise direction, starting from the angle a1 and ending when it reaches a2. 💅

those angle values are in 16.16 fixed point format, and the math is lowkey cute:

  • 256 equals a full circle 🌈
  • 64 equals a right angle ⭐
  • and so on, you get it

Zero is to the right of the centre point, and larger values rotate anticlockwise from there. no cap. 🔥

example time, because seeing it is believing:

/* Draw a black arc from 4 to 1 o'clock. */
arc(screen, SCREEN_W/2, SCREEN_H/2,
    itofix(-21), itofix(43), 50, makecol(0, 0, 0));

not me using itofix() to turn regular numbers into fixed point so the arc actually knows what angle I mean 😭 that's the whole trick, bestie.

👑 SEE ALSO 👑

psa: angles are fixed point, not plain ints. if your arc is acting weird, that's why. itofix() is your friend, fr fr. 🫶

and that's the whole page, bestie — this was Allegro, version 4.4.3, and yeah it's still filed under arc(3). go draw something pretty. 💖🧚✨

📦 where this page comes from