get_camera_matrix (3) - Linux Manuals
get_camera_matrix: Constructs a camera matrix for perspective projection. Allegro game programming library.
NAMEget_camera_matrix - Constructs a camera matrix for perspective projection. Allegro game programming library.
DESCRIPTIONConstructs a camera matrix for translating world-space objects into a normalised view space, ready for the perspective projection. The x, y, and z parameters specify the camera position, xfront, yfront, and zfront are the 'in front' vector specifying which way the camera is facing (this can be any length: normalisation is not required), and xup, yup, and zup are the 'up' direction vector.
The fov parameter specifies the field of view (ie. width of the camera focus) in binary, 256 degrees to the circle format. For typical projections, a field of view in the region 32-48 will work well. 64 (90°) applies no extra scaling - so something which is one unit away from the viewer will be directly scaled to the viewport. 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.
Finally, the aspect ratio is used to scale the Y dimensions of the image relative to the X axis, so you can use it 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). Typically, you will pass (float)w/(float)h, where w and h are the parameters you passed to set_projection_viewport.
Note that versions prior to 4.1.0 multiplied this aspect ratio by 4/3.