Path: chuka.playstation.co.uk!news
From: Steve Hunt <steve@itallnight.u-net.com>
Newsgroups: scee.yaroze.programming.2d_graphics
Subject: 2d1.c Code Fix
Date: Sun, 12 Apr 1998 14:43:11 +0100
Organization: PlayStation Net Yaroze (SCEE)
Lines: 95
Message-ID: <3530C4EF.1754@itallnight.u-net.com>
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Hi all,

	Well i've just got my Yaroze and I'm just finding my feet.

	I've downloaded some demo code and there seems to be a bug 
	in the 2d1.c file.

	The bug is where it calcs the sprite offset(u,v) and tpage number.
	The function FindTopLeftOfTexturePage returns incorrect data if your
	TIM is not tpage x aligned, 
	
	anyway here is the fixed and optimised code if anyone else has had
problems.

	Enjoy,

	Steve




// find coords wrt tpage top left points
void FindTopLeftOfTexturePage(GsIMAGE* imageInfo,
			   int* x, int* y, int* u, int* v,
			   int widthCompression)
{
int testX, testY;
int offset;

	testX = imageInfo->px;
	testY = imageInfo->py;

	*u = 0;
	*v = 0;

 	// calc offset and alaign testX with texture page
	offset = testX & 63;
	testX -= offset;
	(*u) = offset * widthCompression;

 	// calc offset and alaign testY with texture page
	offset = testY & 255;
	testY -= offset;
	(*v) = offset;

	*x = testX;
	*y = testY;
}

You also need to have this as well:

void LinkSpriteToImageInfo (GsSPRITE* sprite, GsIMAGE* imageInfo)
{
	int widthCompression;	  // on frame buffer
	int tPageType;
	int texturePageX, texturePageY, xOffset, yOffset;

	InitGsSprite(sprite);

	switch(imageInfo->pmode) {
		case 0:		   	// 16-bit
			sprite->attribute |= SIXTEEN_BIT_MASK;
			widthCompression = 1;
			tPageType = 2;
			break;
		case 8:		   	// 4-bit
			widthCompression = 4;
			tPageType = 0;
			sprite->cx = imageInfo->cx;
			sprite->cy = imageInfo->cy;
			break;
		case 9:		   	// 8-bit
			sprite->attribute |= EIGHT_BIT_MASK;
			widthCompression = 2;
			tPageType = 1;
			sprite->cx = imageInfo->cx;
			sprite->cy = imageInfo->cy;
			break;
		default:
			printf("Only 4, 8 and 16 bit modes supported\n");
			assert(FALSE);		// other modes not supported
	}

	FindTopLeftOfTexturePage(imageInfo,
		&texturePageX, &texturePageY, &xOffset, &yOffset, widthCompression);

	sprite->tpage
			= GetTPage(tPageType, 0, texturePageX, texturePageY);

	sprite->w = imageInfo->pw * widthCompression;
	sprite->h = imageInfo->ph;

	sprite->u = xOffset;
	sprite->v = yOffset;
}