void al_perspective_transform(ALLEGRO_TRANSFORM *trans,
float left, float top, float n,
float right, float bottom, float f)
Like al_orthographic_transform(3alleg5) but honors perspective. If everything is at a z-position of -near it will look the same as with an orthographic transformation.
To use a specific horizontal field of view you can use the relation:
tan(hfov / 2) = (right - left) / 2 / near