quakeforge-old/common/gl_warp.c

/*
	gl_warp.c

	Sky and water polygons

	Copyright (C) 1996-1997  Id Software, Inc.
	Copyright (C) 1999,2000  Nelson Rush.
	Copyright (C) 1999,2000  contributors of the QuakeForge project
	Please see the file "AUTHORS" for a list of contributors

	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:

		Free Software Foundation, Inc.
		59 Temple Place - Suite 330
		Boston, MA  02111-1307, USA

	$Id$
*/

#include <qtypes.h>
#include <quakedef.h>
#include <glquake.h>
#include <mathlib.h>
#include <sys.h>
#include <console.h>

extern	model_t	*loadmodel;

int		skytexturenum;

int		solidskytexture;
int		alphaskytexture;
float	speedscale;		// for top sky and bottom sky

msurface_t	*warpface;

extern cvar_t *gl_subdivide_size;

/*
	BoundPoly (int, float, vec3_t, vec3_t)
*/
void
BoundPoly (int numverts, float *verts, vec3_t mins, vec3_t maxs) {

	int		i, j;
	float	*v;

	mins[0] = mins[1] = mins[2] = 9999;
	maxs[0] = maxs[1] = maxs[2] = -9999;
	v = verts;
	for (i=0 ; i<numverts ; i++)
		for (j=0 ; j<3 ; j++, v++) {
			if (*v < mins[j])
				mins[j] = *v;
			if (*v > maxs[j])
				maxs[j] = *v;
		}
}

void
SubdividePolygon ( int numverts, float *verts ) {

	int		i, j, k;
	vec3_t	mins, maxs;
	float	m;
	float	*v;
	vec3_t	front[64], back[64];
	int		f, b;
	float	dist[64];
	float	frac;
	glpoly_t	*poly;
	float	s, t;

	if (numverts > 60)
		Sys_Error ("numverts = %i", numverts);

	BoundPoly (numverts, verts, mins, maxs);

	for (i=0 ; i<3 ; i++) {
		m = (mins[i] + maxs[i]) * 0.5;
		m = gl_subdivide_size->value * floor (m/gl_subdivide_size->value + 0.5);
		if (maxs[i] - m < 8)
			continue;
		if (m - mins[i] < 8)
			continue;

		// cut it
		v = verts + i;
		for (j=0 ; j<numverts ; j++, v+= 3)
			dist[j] = *v - m;

		// wrap cases
		dist[j] = dist[0];
		v-=i;
		VectorCopy (verts, v);

		f = b = 0;
		v = verts;
		for (j=0 ; j<numverts ; j++, v+= 3) {
			if (dist[j] >= 0) {
				VectorCopy (v, front[f]);
				f++;
			}
			if (dist[j] <= 0) {
				VectorCopy (v, back[b]);
				b++;
			}
			if (dist[j] == 0 || dist[j+1] == 0)
				continue;
			if ( (dist[j] > 0) != (dist[j+1] > 0) ) {
				// clip point
				frac = dist[j] / (dist[j] - dist[j+1]);
				for (k=0 ; k<3 ; k++)
					front[f][k] = back[b][k] = v[k] + frac*(v[3+k] - v[k]);
				f++;
				b++;
			}
		}

		SubdividePolygon (f, front[0]);
		SubdividePolygon (b, back[0]);
		return;
	}

	poly = Hunk_Alloc (sizeof(glpoly_t) + (numverts-4) * VERTEXSIZE*sizeof(float));
	poly->next = warpface->polys;
	warpface->polys = poly;
	poly->numverts = numverts;
	for (i=0 ; i<numverts ; i++, verts+= 3) {
		VectorCopy (verts, poly->verts[i]);
		s = DotProduct (verts, warpface->texinfo->vecs[0]);
		t = DotProduct (verts, warpface->texinfo->vecs[1]);
		poly->verts[i][3] = s;
		poly->verts[i][4] = t;
	}
}

/*
	GL_SubdivideSurface

	Break a polygon up along axial 64 unit boundaries so that turbulent
	and sky warps can be done reasonably.
*/
void
GL_SubdivideSurface (msurface_t *fa) {

	vec3_t		verts[64];
	int			numverts;
	int			i;
	int			lindex;
	float		*vec;

	warpface = fa;

	/*
		convert edges back to a normal polygon
	*/
	numverts = 0;
	for (i=0 ; i<fa->numedges ; i++) {
		lindex = loadmodel->surfedges[fa->firstedge + i];

		if (lindex > 0)
			vec = loadmodel->vertexes[loadmodel->edges[lindex].v[0]].position;
		else
			vec = loadmodel->vertexes[loadmodel->edges[-lindex].v[1]].position;
		VectorCopy (vec, verts[numverts]);
		numverts++;
	}

	SubdividePolygon (numverts, verts[0]);
}

//=========================================================



// speed up sin calculations - Ed
float	turbsin[] = {
#include "gl_warp_sin.-c"
};

#define TURBSCALE (256.0 / (2 * M_PI))

/*
	EmitWaterPolys

	Do a water warp on the pre-fragmented glpoly_t chain
*/
void
EmitWaterPolys ( msurface_t *fa ) {

	glpoly_t	*p;
	float		*v;
	int			i;
	float		s, t, os, ot;
	vec3_t		nv;

	for (p=fa->polys ; p ; p=p->next) {
		glBegin (GL_POLYGON);
		for (i=0,v=p->verts[0] ; i<p->numverts ; i++, v+=VERTEXSIZE) {
			os = v[3];
			ot = v[4];

			s = os + turbsin[(int)((ot*0.125+realtime) * TURBSCALE) & 255];
			s *= (1.0/64);

			t = ot + turbsin[(int)((os*0.125+realtime) * TURBSCALE) & 255];
			t *= (1.0/64);

			glTexCoord2f (s, t);

			if(r_waterripple->value) {
				nv[0] = v[0]; //+8*sin(v[1]*0.05+realtime)*sin(v[2]*0.05+realtime);
				nv[1] = v[1]; //+8*sin(v[0]*0.05+realtime)*sin(v[2]*0.05+realtime);
				nv[2] = v[2] + r_waterripple->value*sin(v[0]*0.05+realtime)*sin(v[2]*0.05+realtime);
				glVertex3fv (nv);
			} else {
				glVertex3fv (v);
			}
		}
		glEnd ();
	}
}

/*
	EmitSkyPolys
*/
void
EmitSkyPolys ( msurface_t *fa ) {

	glpoly_t	*p;
	float		*v;
	int			i;
	float	s, t;
	vec3_t	dir;
	float	length;

	for (p=fa->polys ; p ; p=p->next)
	{
		glBegin (GL_POLYGON);
		for (i=0,v=p->verts[0] ; i<p->numverts ; i++, v+=VERTEXSIZE)
		{
			VectorSubtract (v, r_origin, dir);
			dir[2] *= 3;	// flatten the sphere

			length = dir[0]*dir[0] + dir[1]*dir[1] + dir[2]*dir[2];
			length = sqrt (length);
			length = 6*63/length;

			dir[0] *= length;
			dir[1] *= length;

			s = (speedscale + dir[0]) * (1.0/128);
			t = (speedscale + dir[1]) * (1.0/128);

			glTexCoord2f (s, t);
			glVertex3fv (v);
		}
		glEnd ();
	}
}

/*
	EmitBothSkyLayers

	Do a sky warp on the pre-fragmented glpoly_t chain. This will be
	called for brushmodels, the world will have them chained together.
*/
void
EmitBothSkyLayers ( msurface_t *fa ) {
	GL_DisableMultitexture();

	GL_Bind (solidskytexture);
	speedscale = realtime*8;
	speedscale -= (int)speedscale & ~127 ;

	EmitSkyPolys (fa);

	glEnable (GL_BLEND);
	GL_Bind (alphaskytexture);
	speedscale = realtime*16;
	speedscale -= (int)speedscale & ~127 ;

	EmitSkyPolys (fa);

	glDisable (GL_BLEND);
}


/*
	Quake 2 sky rendering ("skyboxes")
*/

#define	SKY_TEX		2000

/*
	TARGA LOADING
*/

typedef struct _TargaHeader {
	unsigned char 	id_length, colormap_type, image_type;
	unsigned short	colormap_index, colormap_length;
	unsigned char	colormap_size;
	unsigned short	x_origin, y_origin, width, height;
	unsigned char	pixel_size, attributes;
} TargaHeader;


int
QgetLittleShort ( QFile *f ) {

	byte	b1, b2;

	b1 = Qgetc(f);
	b2 = Qgetc(f);

	return (short)(b1 + b2*256);
}

int
QgetLittleLong (QFile *f) {

	byte	b1, b2, b3, b4;

	b1 = Qgetc(f);
	b2 = Qgetc(f);
	b3 = Qgetc(f);
	b4 = Qgetc(f);

	return b1 + (b2<<8) + (b3<<16) + (b4<<24);
}

/*
	LoadTGA
*/
void
LoadTGA (QFile *fin, byte **targa_rgba) {

	int		columns, rows, numPixels;
	byte		*pixbuf;
	int		row, column;
	TargaHeader	targa_header;
	unsigned char	red = 0, green = 0, blue = 0, alphabyte = 0;

	targa_header.id_length = Qgetc(fin);
	targa_header.colormap_type = Qgetc(fin);
	targa_header.image_type = Qgetc(fin);

	targa_header.colormap_index = QgetLittleShort(fin);
	targa_header.colormap_length = QgetLittleShort(fin);
	targa_header.colormap_size = Qgetc(fin);
	targa_header.x_origin = QgetLittleShort(fin);
	targa_header.y_origin = QgetLittleShort(fin);
	targa_header.width = QgetLittleShort(fin);
	targa_header.height = QgetLittleShort(fin);
	targa_header.pixel_size = Qgetc(fin);
	targa_header.attributes = Qgetc(fin);

	if (targa_header.image_type!=2 && targa_header.image_type!=10)
		Sys_Error ("LoadTGA: Only type 2 and 10 targa RGB images supported\n");

	if (targa_header.colormap_type !=0 ||
			(targa_header.pixel_size!=32 && targa_header.pixel_size!=24)) {
		Sys_Error ("Texture_LoadTGA: Only 32 or 24 bit images supported (no colormaps)\n");
	}

	columns = targa_header.width;
	rows = targa_header.height;
	numPixels = columns * rows;

	*targa_rgba = malloc (numPixels*4);

	if (targa_header.id_length != 0)
		Qseek(fin, targa_header.id_length, SEEK_CUR);  // skip TARGA image comment

	if (targa_header.image_type==2) {  // Uncompressed, RGB images
		for(row=rows-1; row>=0; row--) {
			pixbuf = *targa_rgba + row*columns*4;
			for(column=0; column<columns; column++) {
				switch (targa_header.pixel_size) {
					case 24:

							blue = Qgetc(fin);
							green = Qgetc(fin);
							red = Qgetc(fin);
							*pixbuf++ = red;
							*pixbuf++ = green;
							*pixbuf++ = blue;
							*pixbuf++ = 255;
							break;
					case 32:
							blue = Qgetc(fin);
							green = Qgetc(fin);
							red = Qgetc(fin);
							alphabyte = Qgetc(fin);
							*pixbuf++ = red;
							*pixbuf++ = green;
							*pixbuf++ = blue;
							*pixbuf++ = alphabyte;
							break;
				}
			}
		}
	}
	else if (targa_header.image_type==10) {   // Runlength encoded RGB images
		unsigned char packetHeader,packetSize,j;
		for(row=rows-1; row>=0; row--) {
			pixbuf = *targa_rgba + row*columns*4;
			for(column=0; column<columns; ) {
				packetHeader=Qgetc(fin);
				packetSize = 1 + (packetHeader & 0x7f);
				if (packetHeader & 0x80) {        // run-length packet
					switch (targa_header.pixel_size) {
						case 24:
								blue = Qgetc(fin);
								green = Qgetc(fin);
								red = Qgetc(fin);
								alphabyte = 255;
								break;
						case 32:
								blue = Qgetc(fin);
								green = Qgetc(fin);
								red = Qgetc(fin);
								alphabyte = Qgetc(fin);
								break;
					}

					for(j=0;j<packetSize;j++) {
						*pixbuf++=red;
						*pixbuf++=green;
						*pixbuf++=blue;
						*pixbuf++=alphabyte;
						column++;
						if (column==columns) { // run spans across rows
							column=0;
							if (row>0)
								row--;
							else
								goto breakOut;
							pixbuf = *targa_rgba + row*columns*4;
						}
					}
				}
				else {                            // non run-length packet
					for(j=0;j<packetSize;j++) {
						switch (targa_header.pixel_size) {
							case 24:
									blue = Qgetc(fin);
									green = Qgetc(fin);
									red = Qgetc(fin);
									*pixbuf++ = red;
									*pixbuf++ = green;
									*pixbuf++ = blue;
									*pixbuf++ = 255;
									break;
							case 32:
									blue = Qgetc(fin);
									green = Qgetc(fin);
									red = Qgetc(fin);
									alphabyte = Qgetc(fin);
									*pixbuf++ = red;
									*pixbuf++ = green;
									*pixbuf++ = blue;
									*pixbuf++ = alphabyte;
									break;
						}
						column++;
						if (column==columns) { // pixel packet run spans across rows
							column=0;
							if (row>0)
								row--;
							else
								goto breakOut;
							pixbuf = *targa_rgba + row*columns*4;
						}
					}
				}
			}
			breakOut:;
		}
	}
	Qclose(fin);
	// fclose(fin);
}

/*
	R_LoadSkys
*/
char	*suf[6] = {"rt", "bk", "lf", "ft", "up", "dn"};

void
R_LoadSkys ( void ) {

	int	i;
	QFile	*f;
	byte	*skyimage = NULL;
	char	name[64];

	for (i=0 ; i<6 ; i++) {
		GL_Bind (SKY_TEX + i);
		snprintf(name, sizeof(name), "env/%s%s.tga",
//		snprintf(name, sizeof(name), "env/%s%s.pcx",
				r_skyname->string, suf[i]);
		COM_FOpenFile (name, &f);
		if (!f) {
			Con_Printf ("Couldn't load %s\n", name);
			continue;
		}
		LoadTGA (f, &skyimage);
//		LoadPCX (f, &skyimage);

		glTexImage2D (GL_TEXTURE_2D, 0, gl_solid_format, 256, 256, 0, GL_RGBA, GL_UNSIGNED_BYTE, skyimage);
//		glTexImage2D (GL_TEXTURE_2D, 0, gl_solid_format, 256, 256, 0, GL_RGBA, GL_UNSIGNED_BYTE, pcx_rgb);

//		free (targa_rgba);
		free (skyimage);

		glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
		glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	}
}


vec3_t	skyclip[6] = {
	{1,1,0},
	{1,-1,0},
	{0,-1,1},
	{0,1,1},
	{1,0,1},
	{-1,0,1}
};
int	c_sky;

// 1 = s, 2 = t, 3 = 2048
int	st_to_vec[6][3] = {
	{3,-1,2},
	{-3,1,2},

	{1,3,2},
	{-1,-3,2},

	{-2,-1,3},		// 0 degrees yaw, look straight up
	{2,-1,-3}		// look straight down

//	{-1,2,3},
//	{1,2,-3}
};

// s = [0]/[2], t = [1]/[2]
int	vec_to_st[6][3] = {
	{-2,3,1},
	{2,3,-1},

	{1,3,2},
	{-1,3,-2},

	{-2,-1,3},
	{-2,1,-3}

//	{-1,2,3},
//	{1,2,-3}
};

float	skymins[2][6], skymaxs[2][6];

void
DrawSkyPolygon (int nump, vec3_t vecs) {

	int		i,j;
	vec3_t	v, av;
	float	s, t, dv;
	int		axis;
	float	*vp;

	c_sky++;
#if 0
	glBegin (GL_POLYGON);
	for (i=0 ; i<nump ; i++, vecs+=3) {
		VectorAdd(vecs, r_origin, v);
		glVertex3fv (v);
	}
	glEnd();
	return;
#endif
	// decide which face it maps to
	VectorCopy (vec3_origin, v);
	for (i=0, vp=vecs ; i<nump ; i++, vp+=3) {
		VectorAdd (vp, v, v);
	}
	av[0] = fabs(v[0]);
	av[1] = fabs(v[1]);
	av[2] = fabs(v[2]);
	if (av[0] > av[1] && av[0] > av[2]) {
		if (v[0] < 0)
			axis = 1;
		else
			axis = 0;
	} else if (av[1] > av[2] && av[1] > av[0]) {
		if (v[1] < 0)
			axis = 3;
		else
			axis = 2;
	} else {
		if (v[2] < 0)
			axis = 5;
		else
			axis = 4;
	}

	// project new texture coords
	for (i=0 ; i<nump ; i++, vecs+=3) {
		j = vec_to_st[axis][2];
		if (j > 0)
			dv = vecs[j - 1];
		else
			dv = -vecs[-j - 1];

		j = vec_to_st[axis][0];
		if (j < 0)
			s = -vecs[-j -1] / dv;
		else
			s = vecs[j-1] / dv;
		j = vec_to_st[axis][1];
		if (j < 0)
			t = -vecs[-j -1] / dv;
		else
			t = vecs[j-1] / dv;

		if (s < skymins[0][axis])
			skymins[0][axis] = s;
		if (t < skymins[1][axis])
			skymins[1][axis] = t;
		if (s > skymaxs[0][axis])
			skymaxs[0][axis] = s;
		if (t > skymaxs[1][axis])
			skymaxs[1][axis] = t;
	}
}

#define	MAX_CLIP_VERTS	64
void
ClipSkyPolygon (int nump, vec3_t vecs, int stage) {

	float	*norm;
	float	*v;
	qboolean	front, back;
	float	d, e;
	float	dists[MAX_CLIP_VERTS];
	int		sides[MAX_CLIP_VERTS];
	vec3_t	newv[2][MAX_CLIP_VERTS];
	int		newc[2];
	int		i, j;

	if (nump > MAX_CLIP_VERTS-2)
		Sys_Error ("ClipSkyPolygon: MAX_CLIP_VERTS");
	if (stage == 6) {	// fully clipped, so draw it
		DrawSkyPolygon (nump, vecs);
		return;
	}

	front = back = false;
	norm = skyclip[stage];
	for (i=0, v = vecs ; i<nump ; i++, v+=3) {
		d = DotProduct (v, norm);
		if (d > ON_EPSILON) {
			front = true;
			sides[i] = SIDE_FRONT;
		} else if (d < ON_EPSILON) {
			back = true;
			sides[i] = SIDE_BACK;
		} else
			sides[i] = SIDE_ON;
		dists[i] = d;
	}

	if (!front || !back) {	// not clipped
		ClipSkyPolygon (nump, vecs, stage+1);
		return;
	}

	// clip it
	sides[i] = sides[0];
	dists[i] = dists[0];
	VectorCopy (vecs, (vecs+(i*3)) );
	newc[0] = newc[1] = 0;

	for (i=0, v = vecs ; i<nump ; i++, v+=3) {
		switch (sides[i]) {
			case SIDE_FRONT:
				VectorCopy (v, newv[0][newc[0]]);
				newc[0]++;
				break;
			case SIDE_BACK:
				VectorCopy (v, newv[1][newc[1]]);
				newc[1]++;
				break;
			case SIDE_ON:
				VectorCopy (v, newv[0][newc[0]]);
				newc[0]++;
				VectorCopy (v, newv[1][newc[1]]);
				newc[1]++;
				break;
		}

		if (sides[i] == SIDE_ON || sides[i+1] == SIDE_ON || sides[i+1] == sides[i])
			continue;

		d = dists[i] / (dists[i] - dists[i+1]);
		for (j=0 ; j<3 ; j++) {
			e = v[j] + d*(v[j+3] - v[j]);
			newv[0][newc[0]][j] = e;
			newv[1][newc[1]][j] = e;
		}
		newc[0]++;
		newc[1]++;
	}

	// continue
	ClipSkyPolygon (newc[0], newv[0][0], stage+1);
	ClipSkyPolygon (newc[1], newv[1][0], stage+1);
}

/*
	R_DrawSkyChain
*/
void
R_DrawSkyChain (msurface_t *s) {

	msurface_t	*fa;

	int		i;
	vec3_t	verts[MAX_CLIP_VERTS];
	glpoly_t	*p;

	if (r_sky->value)
	{
		c_sky = 0;
		GL_Bind(solidskytexture);

		// calculate vertex values for sky box

		for (fa=s ; fa ; fa=fa->texturechain) {
			for (p=fa->polys ; p ; p=p->next) {
				for (i=0 ; i<p->numverts ; i++) {
					VectorSubtract (p->verts[i], r_origin, verts[i]);
				}
				ClipSkyPolygon (p->numverts, verts[0], 0);
			}
		}
	}
	else
	{
		GL_DisableMultitexture();

		// used when gl_texsort is on
		GL_Bind(solidskytexture);
		speedscale = realtime*8;
		speedscale -= (int)speedscale & ~127 ;

		for (fa=s ; fa ; fa=fa->texturechain)
			EmitSkyPolys (fa);

		glEnable (GL_BLEND);
		GL_Bind (alphaskytexture);
		speedscale = realtime*16;
		speedscale -= (int)speedscale & ~127 ;

		for (fa=s ; fa ; fa=fa->texturechain)
			EmitSkyPolys (fa);

		glDisable (GL_BLEND);
	}
}

/*
	R_ClearSkyBox
*/
void
R_ClearSkyBox (void) {
	int		i;

	for (i=0 ; i<6 ; i++) {
		skymins[0][i] = skymins[1][i] = 9999;
		skymaxs[0][i] = skymaxs[1][i] = -9999;
	}
}

void
MakeSkyVec (float s, float t, int axis) {
	vec3_t		v, b;
	int			j, k;

	b[0] = s*2048;
	b[1] = t*2048;
	b[2] = 2048;

	for (j=0 ; j<3 ; j++) {
		k = st_to_vec[axis][j];
		if (k < 0)
			v[j] = -b[-k - 1];
		else
			v[j] = b[k - 1];
		v[j] += r_origin[j];
	}

	// avoid bilerp seam
	s = (s+1)*0.5;
	t = (t+1)*0.5;

	if (s < 1.0/512)
		s = 1.0/512;
	else if (s > 511.0/512)
		s = 511.0/512;
	if (t < 1.0/512)
		t = 1.0/512;
	else if (t > 511.0/512)
		t = 511.0/512;

	t = 1.0 - t;
	glTexCoord2f (s, t);
	glVertex3fv (v);
}

/*
	R_DrawSkyBox
*/
int	skytexorder[6] = {0,2,1,3,4,5};

void
R_DrawSkyBox (void) {

	int		i;

#if 0
	glEnable (GL_BLEND);
	glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
	glColor4f (1,1,1,0.5);
	glDisable (GL_DEPTH_TEST);
#endif
	for (i=0 ; i<6 ; i++)
	{
		if (skymins[0][i] >= skymaxs[0][i]
		|| skymins[1][i] >= skymaxs[1][i])
			continue;

		GL_Bind (SKY_TEX+skytexorder[i]);
#if 0
		skymins[0][i] = -1;
		skymins[1][i] = -1;
		skymaxs[0][i] = 1;
		skymaxs[1][i] = 1;
#endif
		glBegin (GL_QUADS);
		MakeSkyVec (skymins[0][i], skymins[1][i], i);
		MakeSkyVec (skymins[0][i], skymaxs[1][i], i);
		MakeSkyVec (skymaxs[0][i], skymaxs[1][i], i);
		MakeSkyVec (skymaxs[0][i], skymins[1][i], i);
		glEnd ();
	}
#if 0
	glDisable (GL_BLEND);
	glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
	glColor4f (1,1,1,0.5);
	glEnable (GL_DEPTH_TEST);
#endif
}


/*
	R_InitSky

	A sky texture is 256*128, with the right side being a masked overlay
*/
void
R_InitSky (texture_t *mt) {

	int			i, j, p;
	byte		*src;
	unsigned	trans[128*128];
	unsigned	transpix;
	int			r, g, b;
	unsigned	*rgba;

	src = (byte *)mt + mt->offsets[0];

	// make an average value for the back to avoid
	// a fringe on the top level

	r = g = b = 0;
	for (i=0 ; i<128 ; i++) {
		for (j=0 ; j<128 ; j++) {
			p = src[i*256 + j + 128];
			rgba = &d_8to24table[p];
			trans[(i*128) + j] = *rgba;
			r += ((byte *)rgba)[0];
			g += ((byte *)rgba)[1];
			b += ((byte *)rgba)[2];
		}
	}

	((byte *)&transpix)[0] = r/(128*128);
	((byte *)&transpix)[1] = g/(128*128);
	((byte *)&transpix)[2] = b/(128*128);
	((byte *)&transpix)[3] = 0;

	if (!solidskytexture)
		solidskytexture = texture_extension_number++;
	GL_Bind (solidskytexture );
	glTexImage2D (GL_TEXTURE_2D, 0, gl_solid_format, 128, 128, 0, GL_RGBA, GL_UNSIGNED_BYTE, trans);
	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

	for (i=0 ; i<128 ; i++) {
		for (j=0 ; j<128 ; j++)	{
			p = src[i*256 + j];
			if (p == 0)
				trans[(i*128) + j] = transpix;
			else
				trans[(i*128) + j] = d_8to24table[p];
		}
	}

	if ( !alphaskytexture )
		alphaskytexture = texture_extension_number++;
	GL_Bind(alphaskytexture);
	glTexImage2D (GL_TEXTURE_2D, 0, gl_alpha_format, 128, 128, 0, GL_RGBA, GL_UNSIGNED_BYTE, trans);
	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
}