suse man page for set_projection_viewport

set_projection_viewport(3alleg4)				  Allegro manual				  set_projection_viewport(3alleg4)

NAME
       set_projection_viewport - Sets the viewport used to scale the output of persp_project(). Allegro game programming library.

SYNOPSIS
       #include <allegro.h>

       void set_projection_viewport(int x, int y, int w, int h);

DESCRIPTION
       Sets  the  viewport used to scale the output of the persp_project() function. Pass the dimensions of the screen area you want to draw onto,
       which will typically be 0, 0, SCREEN_W, and SCREEN_H. Also don't forget to pass an appropriate aspect ratio to get_camera_matrix later. The
       width and height you specify here will determine how big your viewport is in 3d space. So if an object in your 3D space is w units wide, it
       will fill the complete screen when you run into it (i.e., if it has a distance of 1.0 after the camera matrix  was  applied.  The  fov  and
       aspect-ratio  parameters  to get_camera_matrix also apply some scaling though, so this isn't always completely true). If you pass -1/-1/2/2
       as parameters, no extra scaling will be performed by the projection.

SEE ALSO
       persp_project(3alleg4), get_camera_matrix(3alleg4), ex3d(3alleg4), excamera(3alleg4), exquat(3alleg4), exscn3d(3alleg4),  exstars(3alleg4),
       exzbuf(3alleg4)

Allegro 							   version 4.4.2				  set_projection_viewport(3alleg4)