al_transform_coordinates_3d_projective - Man Page

#include <allegro5/allegro.h>

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

Transform x, y, z as homogeneous coordinates. This is the same as using al_transform_coordinates_4d(3) with the w coordinate set to 1, then dividing x, y, z by the resulting w. This will provide the same normalized coordinates Allegro will draw to when a projective transform is in effect as set with al_use_projection_transform(3). To get the actual pixel coordinates from those translate and scale like so (w and h would be the pixel dimensions of the target bitmap):

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

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

al_use_transform(3), al_transform_coordinates(3), al_transform_coordinates_3d(3), al_use_projection_transform(3)

al_transform_coordinates_3d(3).