// Scrolling background stuff
// Coded by Scott Evans 9/5/97
// Last modified 24/5/97

#ifndef _BACKGRND_H
#define _BACKGRND_H

#include <mytypes.h>
#include <myspr.h>

// Structure for scrolling background maps

typedef struct
{
	_word x,y,w,h;		// Display area of BG (could use RECT)
	_word rows,columns;	// Size of BG in number of rows and columns
	_word xoff,yoff;	// Offsets into BG
	_byte bw,bh;		// block width and height
	_word u,v;		// offset into tpage of first block sprite
	_word basecy;		// Y pos of 1st CLUT
	GsSPRITE *blocks;	// Pointer to sprites which make up background
	__byte *data;		// BG data, which blocks go where
	SprHeader *hdr;
}SpriteBG;

// Set SpriteBG structure values
	
#define _SetSpriteBG(P,X,Y,W,H,R,C,S,D,XO,YO,BW,BH,U,V,B,HD) \
	(P)->x=(X),(P)->y=(Y),(P)->w=(W),(P)->h=(H),(P)->rows=R,(P)->columns=(C),(P)->blocks=(S),\
	(P)->data=(D),(P)->xoff=(XO),(P)->yoff=(YO),(P)->bw=(BW),(P)->bh=(BH),(P)->u=(U),(P)->v=(V),\
	(P)->basecy=(B),(P)->hdr=(HD)

// Set up background ready for use
//	bg    - address of background structure
//	sh    - location of sprites which make up background
//	tp    - texture page id of sprites
//	r     - display area of background
//	cx,cy - background palette
	
void InitSpriteBG(SpriteBG *bg,SprHeader *sh,_word tp,RECT *r,_word cx,_word cy)
{	
	static GsSPRITE block;
	
	// Get width and height of blocks
	
	_word w=_GetSprPblks(sh)->w,h=_GetSprPblks(sh)->h;	

	// Set sprite parameters and background parameters
	
	_SetSPRITE(&block,noEffects,0,0,w,h,tp,0,0,cx,cy,0x80,0x80,0x80,0,0,ONE,ONE,0);
	_SetSpriteBG(bg,r->x,r->y,r->w,r->h,0,0,&block,0,0,0,w,h,0,0,cy,sh);
}

// Draw background made up of sprites
// 	bg - background to draw
//	ot - ordering table to register background in
//	p  - priority of background 

void GsSortSpriteBG(SpriteBG *bg,GsOT *ot,_word p)
{
	_word x,y=bg->y,r,c,w=bg->w,h=bg->h,offset;
	_byte blkw=bg->bw,blkh=bg->bh,nprow=TPWDTH/blkw,npcol=TPHGHT/blkh;
	__byte blkno;
	
	// Draw the map a row at a time, going down the screen
	
	for(r=0;r<h;r++)
	{
		x=bg->x;
		offset=(r+bg->yoff)*w;	// Calculate y offset into map
		
		for(c=0;c<w;c++)	// Draw one line of blocks
		{
			if(!((blkno=bg->data[c+offset])&0x80))	// -ve values are not drawn
			{
				bg->blocks->x=x;
				bg->blocks->y=y;
				
				// calculate offset into texture page
				
				bg->blocks->u=bg->u+(blkno%nprow)*nprow;
				bg->blocks->v=bg->v+(blkno/blkh)*blkh;
				bg->blocks->cy=_GetSprCLUTy(bg->hdr,blkno,bg->basecy);
				
				GsSortFastSprite(bg->blocks,ot,p);
			}
			
			x+=blkw;	// Next block position
		}
		
		y+=blkh;	// Next line down
	}
}

// Move map up one row

#define _SpriteBGup(P,B) \
		((P)<(B)->rows-(B)->h ? ++(B)->yoff : (P))

// Move map down one row
		
#define _SpriteBGdown(P,B) \
		((P)>0 ? --(B)->yoff : (P))

// Find sprite image number of block in level map at r,c

#define _GetBlockId(b,r,c)\
	((b)->data[(((r+(b)->yoff)<<4)+((r+(b)->yoff)<<2))+(c)])

// Put a block into a level map

#define _SetBlockId(b,r,c,n)\
	(b)->data[(((r+(b)->yoff)<<4)+((r+(b)->yoff)<<2))+(c)]=(n)
	
#endif