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Kool Aid Man Score Position Timing Qeustion


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#1 AlyoshaTAS OFFLINE  

AlyoshaTAS

    Space Invader

  • 25 posts

Posted Thu Apr 21, 2016 4:09 PM

Hi all,

 

I am trying to figure out how the score in Kool Aid Man is positioned but I always come up 1 pixel short.

 

The code is:

 

STA HMOVE

STA Colbrk

STA CTRLPF

LDA #$D0

STA HMP0

LDA #$20

STA HMP1

.

.

.

RESP0

RESP1

.

.

.

WSYNC

HMOVE

 

So I understand that the first part of the code cuases an effect similar to Cosmic Ark 'starfield effect', where one position clock is eaten up every 4 clocks during hblank and the HMove latches are never cleared.

 

Next we get RESP0 , RESP1 right next to each other. So at this point the players are 9 pixels apart.

 

Then we come to a normal WSYNC, HMOVE

 

In the time it takes to register the HMOVE, the 'starfield effect' has moved player0 3 pixels to the left. The HMove itslef will have a net effect moving player0 3 pixels back to the right, and player1 2 pixels to the left.

 

The net effect is that player0 and player1 are 7 pixels apart. But to display the score correctly they should be 8 pixels apart.

 

So my question is, where does the extra pixel come from? I just can't seem to find it. If anyone could help me account for it I would definitely be grateful! (If it's just that the 'starfield effect' is 4 pixels instead of 3, an explanation of why would also be much appreciated.)

 

Thanks for any insights!

 

 






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