get_camera_matrix(3alleg4)

✨ get_camera_matrix ✨

okay so this is from the Allegro manual, bestie — specifically the get_camera_matrix(3alleg4) page, and it's about the Allegro game programming library. it's giving "3D camera setup but make it one function call" 💅

🌸 NAME 🌸

get_camera_matrix — constructs a camera matrix for perspective projection. (yep, that's the whole job. she does one thing and she does it iconically. Allegro game programming library, as established 💖)

🎀 SYNOPSIS 🎀

#include <allegro.h>

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

like. look at that parameter list. she is THOROUGH. 🫶

🦋 DESCRIPTION 🦋

So what's she actually doing? She constructs a camera matrix that translates your world-space objects into a normalised view space, all ready for the perspective projection. Basically she's the girl who takes your 3D world and goes "okay but from this angle though" 📸

Let's break down the cast of characters, because there are a lot of them and they all matter:

• x, y, z — this trio is your camera position. where is the camera standing. that's it, that's the vibe.
• xfront, yfront, zfront — the 'in front' vector, aka which way the camera is facing. and here's the cute part: this can be any length! normalisation is not required. she handles it. no cap. ✨
• xup, yup, zup — the 'up' direction vector. which way is up, philosophically and also mathematically.

now for fov, the field of view — aka the width of the camera focus — expressed in binary, 256 degrees to the circle format. yes bestie, 256 degrees to the circle. that's the format. that's the whole format.

for typical projections, a field of view in the region 32-48 will work well. 64 (that's 90 degrees, for the record) applies no extra scaling — so something which is one unit away from the viewer will be directly scaled to the viewport. neat, right?

and the direction of things:

• a bigger FOV moves you closer to the viewing plane, so more objects will appear 👀
• a smaller FOV moves you away from the viewing plane, which means you see a smaller part of the world 🌍

and finally — the moment we've all been waiting for — the aspect ratio 🎉 she's used to scale the Y dimensions of the image relative to the X axis, so you can use her to adjust the proportions of the 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 like, don't be surprised, okay? 🙈

typically, you will pass (float)w/(float)h, where w and h are the parameters you passed to set_projection_viewport. iykyk.

⚠️ lowkey important lore drop: versions prior to 4.1.0 multiplied this aspect ratio by 4/3. so if you're on old Allegro and your proportions are doing something weird... that's why bestie. that's the reason. 💀

💜 SEE ALSO 💜

go read these next, they're all part of the same friend group:

• apply_matrix(3alleg4)
• get_align_matrix(3alleg4)
• set_projection_viewport(3alleg4)
• persp_project(3alleg4)

and that's the page, babes 🎀 this was Allegro, version 4.4.3 — mwah, take care of your cameras, stay normalised (except the front vector, she's exempt), and slay 💅✨🦋