Path: chuka.playstation.co.uk!news
From: Alex Herbert <aherbert@ndirect.co.uk>
Newsgroups: scee.yaroze.programming.2d_graphics
Subject: Re: Speed of ClearImage & MoveImage as putpixels
Date: Fri, 06 Feb 1998 15:07:38 +0000
Organization: PlayStation Net Yaroze (SCEE)
Lines: 61
Message-ID: <34DB2739.6DBFCB37@ndirect.co.uk>
References: <34DA30A9.1AE@manc.u-net.com>
Reply-To: aherbert@ndirect.co.uk
NNTP-Posting-Host: dialin1-35.ndirect.co.uk
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Mailer: Mozilla 4.04 [en] (Win95; I)
To: James Shaughnessy <james@manc.u-net.com>

Just a thought...

Isn't it quicker to use a single pixel sprite or line?

Alex


James Shaughnessy wrote:

> Ok, putpixels went out with the Ark considering what the GPU can do
> but I use them for my 2D game, Gravitation, to get pixel-perfect
> collision-detection (a necessity for the type of game, although
> I do most putpixels in the D-Cache).
> As you will no-doubt know a pixel can be defined as a RECT with a
> width and height of 1, so assuming I have globally defined:
>
> RECT pixel, clutpixel;
> pixel.w = 1; pixel.h = 1;
> clutpixel.x = CLUTxpos;         // vertical clut (y variable)
> clutpixel.w = 1;                // used to point to location
> clutpixel.h = 1;                // of your clut on frame buffer
>
> Compare these two functions which for simpicity put only black pixel
> at x, y: (assuming that the first pixel in your clut line is black)
>
> void PutBlackPixel_1(short x, short y)
> {
>   pixel.x = x; pixel.y = y;
>   ClearImage(&pixel, 0, 0, 0);
> }
>
> void PutBlackPixel_2(short x, short y)
> {
>   clutpixel.y = 0;
>   MoveImage(&clutpixel, x, y);
> }
>
> The thing is I have found that for single pixels a MoveImage is about
> 10% FASTER than an equivalent ClearImage, so always try and use
> the second type above (of course you can have a CLUT of as many
> colours as you like if you make it yourself, NOT limited to 256).
> The bad news is that I have found that a single call to Move/ClearImage
> takes a whole HSYNC, even when it's only a pixel.  Which means
> your limited to about 240 NTSC or 290 PAL putpixels, so don't even
> think about using it for bitmaps.
> If you think it means you can't use putpixels to make a fast running
> game then check out my demo below which uses NO GPU GsSPRITES or
> Ordering Tables.
> I had to limit the onscreen bullets to about 120 but it's still
> plays at max frame rate.
>
> Jim
> --
> Get Gravitation from here:
> -----------------------------------------
> James Shaughnessy    james@manc.u-net.com
> http://www.netyaroze-europe.com/~shaughnj
> -----------------------------------------