al_transfo...projective(3)

🌸 NAME 🌸

al_transform_coordinates_3d_projective — Allegro 5 API

okay bestie, this is the al_transfo...projective(3) page from the Library Functions Manual (aka the Allegro reference manual), and it's literally here to make your 3D projective-transform math make sense. no cap 💅

✨ SYNOPSIS ✨

#include <allegro5/allegro.h>

void al_transform_coordinates_3d_projective(const ALLEGRO_TRANSFORM *trans,
   float *x, float *y, float *z)

💖 DESCRIPTION 💖

So here's the vibe: this function transforms x, y, and z as homogeneous coordinates. It's the same as using al_transform_coordinates_4d(3) with the w coordinate set to 1, and then dividing x, y, and z by the resulting w. That gives you the same normalized coordinates Allegro will draw to when a projective transform is in effect — the one set with al_use_projection_transform(3). iconic behavior, honestly ✨

Now, to get the actual pixel coordinates from those normalized coordinates, you translate and scale like this — and w and h would be the pixel dimensions of the target bitmap:

x = w / 2 + x * w / 2
y = h / 2 - y * h / 2

Not me handing you the pixel glow-up formula, but here we are 🫶

Parameters:

• trans — Transformation to use.
• x, y, z — Pointers to the coordinates.

Example:

ALLEGRO_TRANSFORM t2;
al_copy_transform(&t2, al_get_current_transform());
al_compose_transform(&t2, al_get_current_projection_transform());

ALLEGRO_TRANSFORM t3;
al_identity_transform(&t3);
al_scale_transform(&t3, 0.5, -0.5);
al_translate_transform(&t3, 0.5, 0.5);
al_scale_transform(&t3, al_get_bitmap_width(al_get_target_bitmap()),
                   al_get_bitmap_height(al_get_target_bitmap()));

al_transform_coordinates_3d_projective(&t2, &x, &y, &z);
// x, y now contain normalized coordinates
al_transform_coordinates(&t3, &x, &y);
// x, y now contain pixel coordinates

Since 5.2.4 — yes bestie, this one has been around since 5.2.4 🎀

🦋 SEE ALSO 🦋

Go peek at these too, iykyk:

• al_use_transform(3)
• al_transform_coordinates(3)
• al_transform_coordinates_3d(3)
• al_use_projection_transform(3)

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kisses and confetti 💋🎀 — source/version: the Allegro reference manual; page: al_transfo...projective(3); date: not shown on this footer, so no invented date here, bestie 🫶