get_camera_matrix(3)

get_camera_matrix 💅

okay bestie so this is a page from the Allegro manual — section 3, the library calls, the good stuff — and it's all about get_camera_matrix, which builds you a camera matrix for perspective projection. game programming realness. let's GO 🎀

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✨ NAME ✨

get_camera_matrix — constructs a camera matrix for perspective projection. Allegro game programming library. that's the whole vibe, no cap.

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🌸 SYNOPSIS 🌸

#include <allegro.h>

void get_camera_matrix(MATRIX *m, fixed x, y, z, xfront, yfront, zfront,
fixed xup, yup, zup, fov, aspect);

like, yes, that's a LOT of fixed args. it's giving "we have options". 💀

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🦋 DESCRIPTION 🦋

So what this bad boy does is construct a camera matrix that translates your world-space objects into a normalised view space, all prepped and ready for the perspective projection. it's the glow-up your 3D coords get before they hit the screen. ✨

Breaking down the parameters, because there are many and we respect them all:

• x, y, z — the camera position. where your little camera guy is standing. 📍
• xfront, yfront, zfront — the 'in front' vector, aka which way the camera is facing. and here's the tea: this can be any length! normalisation is not required, so don't stress about making it pretty first. it's lowkey chill like that. 🫶
• xup, yup, zup — the 'up' direction vector. which way is up. crucial. otherwise your whole world is sideways and that's not the vibe. 🙈

Then we get to fov, the field of view — that's the width of the camera focus, and it's measured in binary, 256 degrees to the circle format (iykyk, Allegro does angles like that). some fov facts for you, bestie:

• for typical projections, a field of view in the region 32-48 will work well. that's the sweet spot, the main character range. 👑
• 64 (which is 90°) applies no extra scaling — so something that is one unit away from the viewer will be directly scaled to the viewport. literally one-to-one. slay.
• a bigger FOV moves you closer to the viewing plane, so more objects will appear. more stuff on screen! 🎉
• a smaller FOV moves you away from the viewing plane, which means you see a smaller part of the world. zoomed-in energy. 🔍

And finally, the aspect ratio. this one is used to scale the Y dimensions of the image relative to the X axis, so you can use it to adjust the proportions of your output image. set it to 1 for no scaling — BUT keep in mind that the projection also performs scaling according to the viewport size, so it's not the only thing touching your proportions, okay? don't be surprised. 🫠

typically you'll pass:

(float)w/(float)h

where w and h are the parameters you passed to set_projection_viewport. matching set, matching energy. 💖

⚠️ important history lesson, bestie: versions prior to 4.1.0 multiplied this aspect ratio by 4/3. so if you're on ancient Allegro and your proportions are looking weird, that's why. not you. it's the version. 💀

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🌈 SEE ALSO 🌈

• apply_matrix(3)
• get_align_matrix(3)
• set_projection_viewport(3)
• persp_project(3)

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and that's the whole page, periodt. 🎀 this was written for Allegro, version 4.4.3, and the page itself is get_camera_matrix(3) — so like, go build something gorgeous with it. bye bestie, ily, go rotate a cube for me. 💜🦋✨