In most systems, a sprite is a graphical resource of limited size that can be moved across the screen without modifying the playfield. Not so on the GameTank. A “sprite” here can have any size (up to 127×127 pixels) but cannot be moved. It will modify the playfield.
The GameTank approach is to completely redraw the entire screen for every frame. This is achieved thanks to the the system's blitter which is theoretically fast enough to update the screen 2 to 3 times per screen refresh, thus maintaining a 60 FPS animation (note: the Atari Lynx follows a similar approach).
In order to achieve maximum efficiency, graphical assets need to be loaded in VRAM using allocate_sprite(). This function specifies a VRAM bank. Sprites can then be drawn by calling queue_draw_sprite(), referencing the SpriteSlot returned by allocate_sprite(). See Importing and Drawing Sprites for further information.
The C SDK provides easy double buffering to avoid any flickering. A typical animation loop in C looks like this:
while(1) {
// Draw stuff
await_draw_queue();
await_vsync(1);
flip_pages();
// Business logic
}