Path: chuka.playstation.co.uk!news
From: Alex Herbert <aherbert@ndirect.co.uk>
Newsgroups: scee.yaroze.programming.2d_graphics
Subject: Re: Fading..
Date: Fri, 15 May 1998 00:42:44 +0000
Organization: PlayStation Net Yaroze (SCEE)
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References: <6j25v8$aek17@chuka.playstation.co.uk> <355A20ED.50CE92BF@netmagic.net>
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Elliott Lee wrote:

> Anders Clerwall wrote:
> >
> > Hi.. I've seen some fading done in many Yaroze programs.. How's it done?
> > If I LoadImage(&pic, (u_long *)picaddr); how do I fade it up/down to/from
> > black??? I really wanna do this.. please help!
> >
> > // Anders
>
> One postscript: Jim and Robert's solutions are currently the best
> way to do it.  If you only modify the RGB intensity values in your
> GsSPRITE structure and say you smoothly decrement/increment them,
> you'll notice some weird flickering as the image's RGB values get
> mapped from whatever internal true color scheme is used into 15-bit color.
>
> - e!
>   tenchi@netmagic.net
>   http://www.netmagic.net/~tenchi/yaroze/

Yep, I agree with that.  Some other points of interest though.

When using the "Box" method of screen fading, it is a good idea to represent
your "Fade Amount" variable as 5-bit (range 0-31) which is native to the
display hardware.  Then simply shift the bits 3 digits to the left when placing
it into GsBOXF's r,g and b values.  This translates the Fade Amount into the
8-digit format as required by the OS.  The result being that you get a
perfectly smooth fade without visible "stepping".  (Well, at 50 or 60fps
anyhow).  However, it does restrict your fade to only 32 frames in length.
Slower fades will always step, due to the 5-bit colour depth.

Or was Anders talking about the other type of fade, where overlaid screen
objects fade into invisiblilty?  This can be achieved with semi-transparent
objects when using the additive or subtractive transparency modes.  (Tick both
"Transparent for black" and "Translucent except black" in TimUtil, and set the
attribute bits correctly in your code.)  Then it's just a case of reducing the
object's r,g and b values to fade.  When r,g and b become zero, the object will
be totally invisible.
Subtractive transparency is perfect for smoke and shadow effects (ie where
light is reduced).  Additive transparency is good for fire, lights, flares,
etc. (where light is created.)


Herbs