Trouble Drawing Missile Correctly

[raiderred]

First time poster here,

 

I am still very new to programming for the Atari 2600. I am trying to get a basic game shell going by modifying some sample code from Kirk Israel that displays a ghost sprite and changes the sprite when the fire button is pressed. From this code I have discovered the fine horizontal positioning method and the skip draw method. I understand how to use the fine horizontal positioning but I am not sure how to modify the draw code to only draw a portion of a missile.

 

drawPlayer1
lda	 #C_P0_HEIGHT-1
dcp	 P0_Y		
bcs	 .doDraw0	
lda	 #0			
.byte $2c			
.doDraw0:
lda	 (P0_Ptr),y	
sta	 GRP0		
rts

 

Ideally I would only like to draw a portion of a missile at a certain fire position. I am not sure if its possible to modify the skipdraw method to enable ENAM0 at a certain scanline or if I need to try a different technique?

 

Any advice or pointers would be appreciated. Thanks!

demo2.asm

[raiderred]

Never mind I figured it out. The Showing Missiles/Ball using PHP trick from the ATARI 2600 ADVANCED PROGRAMMING GUIDE works pretty well. Plus my Scanline logic had way too many operations in it. Programming C# for too long has spoiled me.