calc_spline(3)

📦 version 4.4.3.1, in fedora 43, fedora 44

💖 calc_spline — the Allegro manual, but make it make sense ✨

okay bestie, so this is a page from the Allegro manual (that's the manual name, yes, we're fancy like that 💅) and today's main character is calc_spline(3). Buckle up, it's giving math but make it cute. 🎀

🌸 NAME 🌸

calc_spline — calculates a series of values along a Bezier spline. 🦋

(Also: it lives in the Allegro game programming library, so like, it's a whole vibe.) 💜

✨ SYNOPSIS ✨

#include <allegro.h>

void calc_spline(const int points[8], int npts, int *x, int *y);

yes that's the whole thing, she's compact, she's iconic, she's not gonna waste your time. 👑

🫶 DESCRIPTION 🫶

So what she does: she calculates a series of npts values along a Bezier spline, and stores them in the output x and y arrays. Boom. Done. Slay. 💅

The Bezier curve itself is specified by the four x/y control points in the points array, and the way it's laid out is:

  • points[0] and points[1] contain the coordinates of the first control point
  • points[2] and points[3] are the second point
  • points[4] and points[5] are the third point
  • points[6] and points[7] are the fourth point

(etc., you get the pattern, it just keeps going like that 🧚)

Control points 0 and 3 are the ends of the spline. Control points 1 and 2 are just guides. Important: the curve probably won't pass through points 1 and 2, but bestie they absolutely affect the shape of the curve between points 0 and 3 — because the lines p0-p1 and p2-p3 are tangents</> to the spline. 🌀

The easiest way to think of it (and honestly the only way my brain will accept it) is:

the curve starts at p0, heading in the direction of p1, but curves round so that it arrives at p3 from the direction of p2. 🌈

Not me explaining tangents like it's gossip. 😭 Anyway.

And like, in addition to their role as graphics primitives, spline curves can be useful for constructing smooth paths around a series of control points — as in exspline.c. So if you wanna see this in the wild, that's your girl. 🍓

👀 SEE ALSO 👀

okay that's the whole page, you ate that, go build something smooth and gorgeous with it 🦋✨

this little love letter came to you from Allegro, version 4.4.3 — mwah, periodt 💖👑🎀

📦 where this page comes from