Path: chuka.playstation.co.uk!news
From: James Shaughnessy <james@manc.u-net.com>
Newsgroups: scee.yaroze.programming.2d_graphics
Subject: Re: Transparent screen grabs?
Date: Wed, 21 Oct 1998 13:51:20 +0100
Organization: PlayStation Net Yaroze (SCEE)
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References: <362B0900.27655A77@bristol.ac.uk>
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Yes indeed a good question there.  You say you've tried setting all
the STP bits for each frame -- but are you setting them while
on the frame buffer?  This will take in the order of 100,000 HSyncs
if you are using a LoadImage and a StoreImage for each pixel by my
reckoning, so as you say causes a rediculous slow-down.

Have you tried StoreImage'ing the whole screen to main memory,
then doing some speedy bit-masking to all the pixels, then a quick
LoadImage back to VRAM where the sprite info is?  The code could be:

  RECT screen = {0, activeBuff*240, 320, 240};
  u_long *mainmem = (u_long *)RESERVED_MEM_ADDR; // or use malloc()

  StoreImage(&screen, &mainmem);
  for (i=0; i<320*240/2; i++;)
    mainmem[i] |= (1<<15) + (1<<31);
  LoadImage(&screen_sprite_area, &mainmem);

Note how TWO pixel STP bits are set for each loop execution, so
it only (?) needs to loop about 40,000 times.  It's only doing one
logical OR (as 1<<15 + 1<<31 is evaluated at compile time) so it
should be plenty quick enough and do the trick if no other bright
soul comes up with a better solution.
Later,
Jim


TEJ Madams wrote:
> Hi there,
>          I've been programming the Yaroze for a couple of weeks with
> a small amount of sucess but I've come across a problem. I wanted to
> recreate that 'fade to battle' effect in FFVII and I know how it's
> done but I don't know exactly how to do it. I need to grab the screen
> and make it into a transparent sprite an paste the image back onto
> the screen again after modifying a bit. Now here's my point, to make
> a TIM image transparent, the transparency bits for every pixel in the
> image need to be set but when you grab the screen, these bits aren't
> set. Arse. All the bits in the screen grab (320*240) need to be set
> every frame which slows the frame rate down dramatically. I know it
> can be done quicker but how?
-- 
-----------------------------------------
James Shaughnessy    james@manc.u-net.com
http://www.netyaroze-europe.com/~shaughnj
-----------------------------------------