atari2600land's Blog

Probably that is 7 hardware sprites while something like Space Invaders might draw all the invaders as software sprites, which is more CPU consuming and with more restrictions on colour clashes but how you'd usually do it on systems with no hardware sprites at all.

 

Game Gear, isn't that a portable Master System? I never looked into the specs but I know that on the older VDP based systems including SG-1000, MSX, ColecoVision, TI-99/4A etc the limit is 4 or 5 sprites on the same row before flickering, though it can display up to 32 sprites anywhere on the screen except for this limitation.

On 1/27/2020 at 1:45 PM, carlsson said:

Game Gear, isn't that a portable Master System?

Yes, but has programmable color palette to make 4096 colors for 32 entries, but the screen is visible 160x144 out of 256x192.  Sprites can be either 8x8 or 8x16 with the maximum of 64 sprites.  Only 8 of those on a line.  Possibly there's stray sprites outside the visible screen area that are on scanline. 

Oh yeah now I remember, if a sprite y coordinate's is at 208, all sprites after that are disabled. The VDP inherited that from the tms9918a chip.  So if a burger's sprite is on that coordinate, and if the burger is first to be drawn, and the score is 2nd to be drawn.  Then the score will be dropped.  When I want a sprite to be removed, I move them to 207 to not trip that flag. 

 

 

Oh, cool! Is the 208 on purpose for programs that want a quick way to disable all sprites and then renable them by moving sprite #1 back in a visible position?

Yeah, it's on purpose and documented in the VDP programmer's manual.  You can arbitrarily cut off sprite processing at any number using this method.

Well, that's a good thing to know about the 208 y-axis thing. I wonder how many problems that was causing in earlier programs I attempted to make.

Well, the 0xD0 sentinel is inherited from the TMS99x8 chips.  According to an unofficial GG VDP programmer's manual, it only affects the 4 TMS99x8, 192-line modes.  In the others, including 144 (which apparently is 224 with skipped lines), there are no magic numbers in the sprite vertical positions.  In the 99x8 modes, sprites are either 8x8 or 16x16, while in the other modes they are 8x8 or 8x16.  So if you were using the advanced modes, that shouldn't be an issue and you only have the 8-sprite limitation to worry about.