calc_spline(3alleg4)

💖 calc_spline — NAME 💖

ok so this is calc_spline, and it Calculates a series of values along a Bezier spline. it lives in the Allegro game programming library, and it's page calc_spline(3alleg4) if you're the kind of girlie who cites her sources 💅

✨ SYNOPSIS ✨

#include <allegro.h>

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

like. that's it. that's the whole vibe check. one function, four args, no notes 🎀

🦋 DESCRIPTION 🦋

ok bestie come sit with me because this one is actually so fun once it clicks.

So calc_spline calculates a series of npts values along a Bezier spline, and it stores them in the output x and y arrays. That's the whole job. It hands you back a bunch of points and you go draw them or move something along them or whatever your main character era requires 🌸

Now, the Bezier curve itself is specified by four x/y control points sitting in the points array. And yes the array is declared [8] because that's 4 points × 2 coordinates, math ate that 💀 Here's the breakdown:

• points[0] and points[1] contain the coordinates of the first control point
• points[2] and points[3] are the second point
• etc., etc., you get the pattern, keep going 🫶

So real talk on how these four points actually behave:

• Control points 0 and 3 are the ends of the spline. They're the actual endpoints, the anchors, the moment.
• Points 1 and 2 are guides. They're not where the curve goes, they're where the curve looks.

lowkey important: the curve probably won't pass through points[1] and points[2]. They're not stops on the itinerary, they're the vibe influencers. But 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 ✨

And here's the way to actually hold it in your head, the easiest way to think of it:

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

it's giving "leaving your friend's house but you turn around for one last look and then you're gone" 😭 the departure direction and the arrival direction are doing all the work, the middle is just physics.

And not for nothing — besides their whole role as graphics primitives, spline curves can be genuinely useful for constructing smooth paths around a series of control points, exactly like they do in exspline.c. so if you wanna see it living its truth in the wild, go peek at that one. iconic behavior, no cap 💜

👑 SEE ALSO 👑

• spline(3alleg4)
• exspline(3alleg4)

and that's the page fr fr 🎀 this was Allegro, version 4.4.3, and we're out here on calc_spline(3alleg4) — go make something smooth, bestie, you're gonna slay 🌈💖