Path: chuka.playstation.co.uk!scea!greg_labrec@interactive.sony.com
From: mperdue@iquest.net (Mario Perdue)
Newsgroups: scea.yaroze.programming.2d_graphics
Subject: Re: pixels
Date: Mon, 07 Jul 1997 20:36:33 GMT
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On Mon, 07 Jul 1997 17:13:32 GMT, jamin1@psu.edu (Jamin Frederick)
wrote:

>Hi, how's it going?  I'm working on my pixel-by-pixel collision
>detection algorithm, and I've run into a problem of actually trying to
>access pixel data of sprites.  It seems like I won't be able to access
>the data the lies in the video memory once it has been transferred
>from the main memory, since there are no api calls to do this, plus,
>trying to access this memory probably interferes with the video
>syncing and drawing mechanism.  The only thing left to do is use the
>pixel data that's been in main memory from the loaded TIM.
>The only thing is, that this memory could be otherwise used for
>something else.

You can transfer image data from the frame buffer to main memory using
StoreImage().

>So I have pixel data both in the video memory AND in main memory,
>which is sort of redundant, but main memory is the only way to go.
>
>My question is, is there any way to replace data that's already been
>loaded from siocons?  For example, if I loaded my TIM at 0x80090000,
>and then during program execution, I transfer this from main memory to
>video memory, so that I no longer need what's at 0x80090000, is there
>any easy way to reload data back into this position for use?

Since you have a pointer to the memory in question, you can pretty
much do anything you want with it. I'm told the Japanese web site has
a program for loading overlays, but I havn't seen it. Is it easy?
..Define easy. :^)

>The reason I want this to be answered is that I guess I'm planning to
>make my pixel-by-pixel algorithm based on pixel data in main memory,
>and I don't want it to be a silly approach.  I mean, if someone
>actually does want to reclaim use of that main memory, that is, then
>the algorithm will totally fail!  
>
>In general, is it a waste of space to have all your image data sitting
>in main memory?

That depends on the program. If you're short of memory, then it's a
waste. If you've got memory to spare, then it's not a waste.

>Is there any way your program heap can plow past some
>of this  data, once it's been utilized?  Or perhaps have a spot just
>for incoming data and use I/O to reload into that spot during program
>execution...which only CodeWarrior people can do at this point?

As I said above, you've got a pointer to this area and you own the
machine (i.e. you don't have any other programs to share resources
with.) You can do whatever you want with it.

Mario