exquat(3alleg4)                 Allegro manual                 exquat(3alleg4)

       exquat - A comparison between Euler angles and quaternions. Allegro
       game programming library.

       #include <allegro.h>

       Example exquat

       Euler angles are convenient for storing and creating 3D orientations.
       However, this program demonstrates that they are not good when
       interpolating between two different orientations. The problem is solved
       by using Allegro's quaternion operations.

       In this program, two cubes are rotated between random orientations.
       Notice that although they have the same beginning and ending
       orientations, they do not follow the same path between orientations.

       One cube is being rotated by directly incrementing or decrementing the
       Euler angles from the starting point to the ending point.  This is an
       intuitive notion, but it is incorrect because it does not cause the
       object to turn around a single unchanging axis of rotation.  The axis
       of rotation wobbles resulting in the object spinning in strange ways.
       The object will eventually end up in the orientation that the user
       intended, but it gets there in a way that is unattractive.  Imagine if
       this method was used to update the position of a camera in a game!
       Sometimes it would swing wildly and disorient the player.

       The other cube is animated using quaternions. This results in a much
       more pleasing animation because the cube turns around a single axis of

       BITMAP(3alleg4), END_OF_MAIN(3alleg4), MATRIX_f(3alleg4),
       QUAT(3alleg4), acquire_bitmap(3alleg4), allegro_error(3alleg4),
       allegro_init(3alleg4), allegro_message(3alleg4),
       apply_matrix_f(3alleg4), blit(3alleg4), circle(3alleg4),
       clear_keybuf(3alleg4), clear_to_color(3alleg4), create_bitmap(3alleg4),
       desktop_palette(3alleg4), destroy_bitmap(3alleg4), font(3alleg4),
       get_camera_matrix_f(3alleg4), get_rotation_matrix(3alleg4),
       get_rotation_matrix_f(3alleg4), get_rotation_quat(3alleg4),
       install_keyboard(3alleg4), keypressed(3alleg4), line(3alleg4),
       matrix_mul_f(3alleg4), palette_color(3alleg4),
       persp_project_f(3alleg4), quat_interpolate(3alleg4),
       quat_to_matrix(3alleg4), readkey(3alleg4), release_bitmap(3alleg4),
       rest(3alleg4), screen(3alleg4), set_gfx_mode(3alleg4),
       set_palette(3alleg4), set_projection_viewport(3alleg4),

Allegro                          version 4.4.2                 exquat(3alleg4)