Path: chuka.playstation.co.uk!news
From: Chris Chadwick <xjk18@dial.pipex.com>
Newsgroups: scee.yaroze.beginners
Subject: Re: DrawSync confusion.
Date: Tue, 11 Aug 1998 00:56:55 -0700
Organization: PlayStation Net Yaroze (SCEE)
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References: <35c6f063.10719834@news.playstation.co.uk> <35C6F927.4765EF18@scee.sony.co.uk>
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James Russell wrote:
> 
> 1) When you're loading TIMs into VRAM using LoadImage, the GPU will queue up the LoadImage command
> (which means that it doesn't get executed immmediately). When it gets around to processing it, it
> will use the values in the RECT structure that exists at the time of the GPU processing, rather than
> the values that were in the RECT when you did the LoadImage. Thus doing this:
> 
> setRect(&myRect,1,2,3,4);
> LoadImage(&myRect,&myTimData);
> setRect(&myRect,5,6,7,8);
> 
> is more likely to use the _latter_ rectangle instead of the intended former rectangle. To get around
> this, it is advisable to do a DrawSync(0) directly after the LoadImage instruction, which guarantees
> that the values the GPU will use will be the ones you intend.
> 

Are you sure about this? I only ask as I use MoveImage without a subsequent DrawSync and everything
works OK. I use the following function to dynamically create a sprite by using MoveImage to copy
characters from a font TIM into the sprite area of VRAM:

//*------------------------------------------------------------------------------------------
//*	MakeAmmoBarText
//*-------------------------------------------------------------------------------------<???>
void MakeAmmoBarText(char *charp)
{
RECT	src;
int		len=0;
int		destX = timData[TIM_POLYCART].px+31;	//* 31 is 124>>2 because of 4bit pixels
int		destY = timData[TIM_POLYCART].py+40;
int		ascii;
int		fontX = timData[TIM_POLYCART].px+4;

	//* Set font image source rect (constant members)
	src.y = destY;
	src.h = 5;
	src.w = 1;								//* 1 is 4 4bit pixels wide

	//* Copy chars to sprite image area
	while (ascii = *charp++) {
		if (ascii==' ')
			src.x = fontX + 26;				//* Space pattern is after Z
		else
			src.x = fontX + (ascii - 'A');

		MoveImage(&src, destX++, destY);
		len++;
	}

	//* Update .x and .w sprite settings for this text
	ammoText->x = AMMO_BAR_X + ((BAR_MAX - (ammoText->w=len<<2)) >> 1);
}

As you can see, the main loop copies a character at a time from the font TIM using
MoveImage (altering the RECT on each iteration!) without a subsequent DrawSync. This is
vital as this function will be called from within the main game loop where a DrawSync
issued anywhere other than before the main VSync would cause havoc.

When I queried the EXACT operation of MoveImage a couple of months back, I was told
(by someone at tech support, I think) it was OK to do this as a copy of the RECT is made
when the MoveImage request is put in the GPU queue. Thus, the RECT can be altered
immediately after MoveImage without fear of getting undesirable results. This indeed
appears to be the case as the above function works fine.

I would, then, be very surprised if LoadImage doesnt also operate in the same manner
by storing a copy of the RECT when executed. Then again, I've been surprised before :)

Regards,

-Chris