/*
Copyright (C) Manoel Kasimier
Copyright (C) 1996-1997 Id Software, Inc.

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

*/
// d_sky.c

#include "globaldef.h"
#include "r_local.h"
#include "d_local.h"

#define SKY_SPAN_SHIFT	5
#define SKY_SPAN_MAX	(1 << SKY_SPAN_SHIFT)

extern qboolean	r_dowarp;
static float   timespeed1, timespeed2; 
extern byte   *skyunderlay, *skyoverlay;

/*
=================
D_Sky_uv_To_st
=================
*/
void D_Sky_uv_To_st (int u, int v, fixed16_t *s, fixed16_t *t, fixed16_t *s2, fixed16_t *t2)
{
	float   wu, wv;
	vec3_t   end;

	wu = (u - xcenter) / xscale;
	wv = (ycenter - v) / yscale;

	end[0] = vpn[0] + wu*vright[0] + wv*vup[0];
	end[1] = vpn[1] + wu*vright[1] + wv*vup[1];
	end[2] = vpn[2] + wu*vright[2] + wv*vup[2];

	end[2] *= 3;
	VectorNormalize (end);
	*s = (int)((timespeed1 + 6*(SKYSIZE/2-1)*end[0]) * 0x10000);
	*t = (int)((timespeed1 + 6*(SKYSIZE/2-1)*end[1]) * 0x10000); 
	*s2 = (int)((timespeed2 + 6*(SKYSIZE/2-1)*end[0]) * 0x10000);
	*t2 = (int)((timespeed2 + 6*(SKYSIZE/2-1)*end[1]) * 0x10000);
}

unsigned char D_DrawSkyPixelOpaque (unsigned char pixel1, unsigned char pixel2)
{
	return pixel2 ? pixel2 : pixel1;
}

/*
=================
D_DrawSkyScans8
=================
*/
void D_DrawSkyScans8 (espan_t *pspan)
{
	int            count, spancount, u, v;
	unsigned char   *pdest;
	fixed16_t      s, t, snext, tnext, sstep, tstep;
	int            spancountminus1;

	fixed16_t      s2, t2, snext2, tnext2, sstep2, tstep2; 
	timespeed1=skytime*skyspeed;//*4; // Fightoon modification
	timespeed2=timespeed1*2.0;//*-1; // Fightoon modification
	sstep2 = 0;
	tstep2 = 0;

	sstep = 0;   // keep compiler happy
	tstep = 0;   // ditto

	do
	{
		pdest = (unsigned char *)((byte *)d_viewbuffer + (screenwidth * pspan->v) + pspan->u);
		count = pspan->count;

		u = pspan->u;
		v = pspan->v;
		D_Sky_uv_To_st (u, v, &s, &t, &s2, &t2); 

		do
		{
			if (count >= SKY_SPAN_MAX)
				spancount = SKY_SPAN_MAX;
			else
				spancount = count;

			count -= spancount;

			if (count)
             		{
				u += spancount;

				// calculate s and t at far end of span,
				// calculate s and t steps across span by shifting
				D_Sky_uv_To_st (u, v, &snext, &tnext, &snext2, &tnext2); 
                
				sstep = (snext - s) >> SKY_SPAN_SHIFT;
				tstep = (tnext - t) >> SKY_SPAN_SHIFT;

				sstep2 = (snext2 - s2) >> SKY_SPAN_SHIFT;
				tstep2 = (tnext2 - t2) >> SKY_SPAN_SHIFT;
			}
			else
			{
				// calculate s and t at last pixel in span,
				// calculate s and t steps across span by division
				spancountminus1 = (float)(spancount - 1);

				if (spancountminus1 > 0)
				{
					u += spancountminus1;
					D_Sky_uv_To_st (u, v, &snext, &tnext, &snext2, &tnext2); 

					sstep = (snext - s) / spancountminus1;
					tstep = (tnext - t) / spancountminus1;
					sstep2 = (snext2 - s2) / spancountminus1; 
					tstep2 = (tnext2 - t2) / spancountminus1; 
				}
			}

			do
			{
				*pdest++ = D_DrawSkyPixelOpaque(skyunderlay[((t  & R_SKY_TMASK) >> 8) + ((s  & R_SKY_SMASK) >> 16)],
				skyoverlay [((t2 & R_SKY_TMASK) >> 8) + ((s2 & R_SKY_SMASK) >> 16)]);
                		s += sstep;
                		t += tstep;
                		s2 += sstep2; 
                		t2 += tstep2; 
             		} while (--spancount > 0);

             		s = snext;
             		t = tnext;
             		s2 = snext2; 
             		t2 = tnext2; 
		} while (count > 0);
	} while ((pspan = pspan->pnext) != NULL);
}