galvaders classes hierarchy chart.
base_image formation
|- bullet |- inv_formation
|- enemy |- gal_fromation
|- explosion
|- player

gal_attack
text_msg
stars
menu


base_image is the basic sprite class.
bullet, enemy, explotion and player classes are derived from base_image class.

inv_fromation and gal_formation are derived from formation class.

The gal_attack, text_msg, stars, and menu are independent.

For each class the first two parameters are RLE_SPRITE **dt and BITMAP *dst that hold the RLE_SPRITE * vector and destination BITMAP pointer.