Re: [stella] When to update sprites

Subject: Re: [stella] When to update sprites
From: "Thomas Jentzsch" <tjentzsch@xxxxxx>
Date: Mon, 15 Oct 2001 11:17:25 +0200
Glenn Saunders wrote:
> Note that only the pedestrians move across the entire screen.  Well, not 
> necessarily the ENTIRE screen.  I can bound them in by 2 playfield pixels on 
> the left or right maximum if necessary, just as long as I start them out 
> behind the safezone.  The cars are bounded between the two safezone (PF0) 
> areas.  So that gains me some time, doesn't it?  If the sprites extend to 
> within 2 playfield pixels of the edge, what is the safe cycle ranges to 
> update?  How much of a window on the right side of the line?  If bounded by 
> PF0 (cars) how much more time to I gain on the left and on the right??

3 pixels give you 1 cycle, so 4 playfield pixels (=16 pixels) will give you about 5 cycles.

> I could have different versions of the kernel that update at different spots 
> depending on the X position of the objects in order to avoid stomping on the 
> sprite while it's being drawn.  If I evaluate the screen as two halves and 
> have two different kernels depending on whether the sprite is on the left or 
> right half, then that's 16 possible combinations if done for all 4 objects.  
> The game is simple enough that even if I went that far it might still fit 
> into 4K.

Well, that's a nice idea and it should work. But I'd try to optimize my single kernel first, and when it finally turns out, that it doesn't work, then I'd try this approach. Then you have a good kernel to start with. And maybe you won't need all 16 combinations, maybe 2 or 4 a sufficient to solve the problem.

> Also, Piero, is this tearing phenomenon what happened with the player's 
> shots in Oystron? 

Ok, I'm not Piero, but still the answer is: Yes! :)
I think, for simple shots in a fast paced game like Oystron, this is a very acceptable compromised result.

Have fun!
Thomas Jentzsch         | *** Every bit is sacred ! ***
tjentzsch at web dot de |

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