Path: chuka.playstation.co.uk!news
From: James Shaughnessy <james@manc.u-net.com>
Newsgroups: scee.yaroze.programming.2d_graphics
Subject: Speed of ClearImage & MoveImage as putpixels
Date: Thu, 05 Feb 1998 21:35:37 +0000
Organization: Bacardi Ferrari V12
Lines: 49
Message-ID: <34DA30A9.1AE@manc.u-net.com>
NNTP-Posting-Host: manc.u-net.com
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Mailer: Mozilla 3.0 (Win95; I)

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
-----------------------------------------