/*
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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

*/
// d_sky.c

#include "quakedef.h"
#include "r_local.h"
#include "d_local.h"

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


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

    if (r_refdef.vrect.width >= r_refdef.vrect.height)
	temp = (float)r_refdef.vrect.width;
    else
	temp = (float)r_refdef.vrect.height;

    wu = 8192.0 * (float)(u - ((int)vid.width >> 1)) / temp;
    wv = 8192.0 * (float)(((int)vid.height >> 1) - v) / temp;

    end[0] = 4096 * vpn[0] + wu * vright[0] + wv * vup[0];
    end[1] = 4096 * vpn[1] + wu * vright[1] + wv * vup[1];
    end[2] = 4096 * vpn[2] + wu * vright[2] + wv * vup[2];
    end[2] *= 3;
    VectorNormalize(end);

    temp = skytime * skyspeed;	// TODO: add D_SetupFrame & set this there
    *s = (int)((temp + 6 * (SKYSIZE / 2 - 1) * end[0]) * 0x10000);
    *t = (int)((temp + 6 * (SKYSIZE / 2 - 1) * end[1]) * 0x10000);
}


/*
=================
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;

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

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

	count = pspan->count;

	// calculate the initial s & t
	u = pspan->u;
	v = pspan->v;
	D_Sky_uv_To_st(u, v, &s, &t);

	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);

		sstep = (snext - s) >> SKY_SPAN_SHIFT;
		tstep = (tnext - t) >> 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);

		    sstep = (snext - s) / spancountminus1;
		    tstep = (tnext - t) / spancountminus1;
		}
	    }

	    do {
		*pdest++ = r_skysource[((t & R_SKY_TMASK) >> 8) +
				       ((s & R_SKY_SMASK) >> 16)];
		s += sstep;
		t += tstep;
	    } while (--spancount > 0);

	    s = snext;
	    t = tnext;

	} while (count > 0);

    } while ((pspan = pspan->pnext) != NULL);
}
