3D Starfield Effect Using Sprites

Just for fun. This program uses hardware sprites to simulate a starfield. There are three sizes of stars, small, medium, and large. The three 'star plains' move at different speeds, giving a 3D effect. You can change the direction of the starfield using the keys E (up) S (left) D (right) and X (down).

Here's a YouTube demo video:

Code

( ** StarField Sprite Demo ** ) VARIABLE StringSpace 82 CHARS ALLOT ( create a string buffer ) StringSpace 84 32 FILL ( initialise it to ASCII 32 ) S" The Power Of Forth!" StringSpace SWAP CMOVE 0 VALUE FlipFlop ( vdp addresses for small, medium, & big star definitions) $1000 CONSTANT Sml* $1008 CONSTANT Med* $1010 CONSTANT Big* ( keyboard codes ) CHAR E CONSTANT KeyE CHAR S CONSTANT KeyS CHAR D CONSTANT KeyD CHAR X CONSTANT KeyX ( define colours ) 15 CONSTANT White 9 CONSTANT TEN ( set up user defined graphics for the 3 star sizes ) : UDG Sml* DATA 4 $8000 0 0 0 2* VMBW ( small star ) Med* DATA 4 $40E0 $4000 0 0 2* VMBW ( medium star ) Big* DATA 4 $70F8 $F870 0 0 2* VMBW ( large star ) ; ( generate a random Y coordinate ) : RndY 180 RND ; ( generate a random X coordinate ) : RndX 256 RND ; ( set up our sprites. 10 small, 10 medium, 10 large ) : 10Small TEN FOR I RndY RndX 0 White SPRITE NEXT ; : 10Med TEN FOR I 10 + RndY RndX 1 White SPRITE NEXT ; : 10Big TEN FOR I 20 + RndY RndX 2 White SPRITE NEXT ; ( set up the sprite movement list for each direction ) : GoLeft TEN FOR I 0 -1 SPRVEC NEXT TEN FOR I 10 + 0 -2 SPRVEC NEXT TEN FOR I 20 + 0 -3 SPRVEC NEXT ; : GoRight TEN FOR I 0 1 SPRVEC NEXT TEN FOR I 10 + 0 2 SPRVEC NEXT TEN FOR I 20 + 0 3 SPRVEC NEXT ; : GoUp TEN FOR I -1 0 SPRVEC NEXT TEN FOR I 10 + -2 0 SPRVEC NEXT TEN FOR I 20 + -3 0 SPRVEC NEXT ; : GoDown TEN FOR I 1 0 SPRVEC NEXT TEN FOR I 10 + 2 0 SPRVEC NEXT TEN FOR I 20 + 3 0 SPRVEC NEXT ; : Delay 100 FOR NEXT ; : DoFlipFlop FlipFlop NOT DUP TO FlipFlop ; : ScanKeys KEY? CASE KeyE OF GoUp ENDOF KeyS OF GoLeft ENDOF KeyD OF GoRight ENDOF KeyX OF GoDown ENDOF 2 OF CR ." Break" CR QUIT ENDOF ENDCASE ; : Scroll DoFlipFlop IF [ StringSpace 83 + LITERAL ] C@ [ StringSpace LITERAL StringSpace 1+ LITERAL ] 83 CMOVE> [ StringSpace LITERAL ] C! 0 0 GOTOXY [ StringSpace 32 + LITERAL ] 31 TYPE 0 23 GOTOXY [ StringSpace 32 + LITERAL ] 31 TYPE ScanKeys THEN ; : Setup 1 GMODE 0 SCREEN UDG 10Small 10Med 10Big GoRight ; : GO Setup BEGIN 0 30 SPRMOV Scroll Delay AGAIN ;