/*
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.

*/
// gl_warp.c -- sky and water polygons

#include "quakedef.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;

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 = (glpoly_t*) 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

Breaks 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;
    texture_t   *t;

    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.h"
};
#define TURBSCALE (256.0 / (2 * M_PI))

/*
=============
EmitWaterPolys

Does 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;


    for (p=fa->polys ; p ; p=p->next)
    {
#ifdef USE_OPENGLES 
        {
            float* pUV = gTexCoordBuffer;
            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);

                *pUV++ = s;
                *pUV++ = t;
            }
        }
        
        glVertexPointer(3, GL_FLOAT, VERTEXSIZE*sizeof(float), &p->verts[0][0]);
        glTexCoordPointer(2, GL_FLOAT, 0, gTexCoordBuffer);
        glDrawArrays(GL_TRIANGLE_FAN, 0, p->numverts);
#else
        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);
            glVertex3fv (v);
        }
        glEnd ();
#endif
    }
}




/*
=============
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)
    {
#ifdef USE_OPENGLES
        {
            float* pUV = gTexCoordBuffer;
            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);

                *pUV++ = s;
                *pUV++ = t;
            }
        }
        
        glVertexPointer(3, GL_FLOAT, VERTEXSIZE*sizeof(float), &p->verts[0][0]);
        glTexCoordPointer(2, GL_FLOAT, 0, gTexCoordBuffer);
        glDrawArrays(GL_TRIANGLE_FAN, 0, p->numverts);
#else
        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 ();
#endif
    }
}

/*
===============
EmitBothSkyLayers

Does 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)
{
    int         i;
    int         lindex;
    float       *vec;

    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);
}

#ifndef QUAKE2
/*
=================
R_DrawSkyChain
=================
*/
void R_DrawSkyChain (msurface_t *s)
{
    msurface_t  *fa;

    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);
}

#endif

/*
=================================================================

  Quake 2 environment sky

=================================================================
*/

#ifdef QUAKE2


#define SKY_TEX     2000

/*
=================================================================

  PCX Loading

=================================================================
*/

typedef struct
{
    char    manufacturer;
    char    version;
    char    encoding;
    char    bits_per_pixel;
    unsigned short  xmin,ymin,xmax,ymax;
    unsigned short  hres,vres;
    unsigned char   palette[48];
    char    reserved;
    char    color_planes;
    unsigned short  bytes_per_line;
    unsigned short  palette_type;
    char    filler[58];
    unsigned    data;           // unbounded
} pcx_t;

byte    *pcx_rgb;

/*
============
LoadPCX
============
*/
void LoadPCX (FILE *f)
{
    pcx_t   *pcx, pcxbuf;
    byte    palette[768];
    byte    *pix;
    int     x, y;
    int     dataByte, runLength;
    int     count;

//
// parse the PCX file
//
    fread (&pcxbuf, 1, sizeof(pcxbuf), f);

    pcx = &pcxbuf;

    if (pcx->manufacturer != 0x0a
        || pcx->version != 5
        || pcx->encoding != 1
        || pcx->bits_per_pixel != 8
        || pcx->xmax >= 320
        || pcx->ymax >= 256)
    {
        Con_Printf ("Bad pcx file\n");
        return;
    }

    // seek to palette
    fseek (f, -768, SEEK_END);
    fread (palette, 1, 768, f);

    fseek (f, sizeof(pcxbuf) - 4, SEEK_SET);

    count = (pcx->xmax+1) * (pcx->ymax+1);
    pcx_rgb = malloc( count * 4);

    for (y=0 ; y<=pcx->ymax ; y++)
    {
        pix = pcx_rgb + 4*y*(pcx->xmax+1);
        for (x=0 ; x<=pcx->ymax ; )
        {
            dataByte = fgetc(f);

            if((dataByte & 0xC0) == 0xC0)
            {
                runLength = dataByte & 0x3F;
                dataByte = fgetc(f);
            }
            else
                runLength = 1;

            while(runLength-- > 0)
            {
                pix[0] = palette[dataByte*3];
                pix[1] = palette[dataByte*3+1];
                pix[2] = palette[dataByte*3+2];
                pix[3] = 255;
                pix += 4;
                x++;
            }
        }
    }
}

/*
=========================================================

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;


TargaHeader     targa_header;
byte            *targa_rgba;

int fgetLittleShort (FILE *f)
{
    byte    b1, b2;

    b1 = fgetc(f);
    b2 = fgetc(f);

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

int fgetLittleLong (FILE *f)
{
    byte    b1, b2, b3, b4;

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

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


/*
=============
LoadTGA
=============
*/
void LoadTGA (FILE *fin)
{
    int             columns, rows, numPixels;
    byte            *pixbuf;
    int             row, column;

    targa_header.id_length = fgetc(fin);
    targa_header.colormap_type = fgetc(fin);
    targa_header.image_type = fgetc(fin);
    
    targa_header.colormap_index = fgetLittleShort(fin);
    targa_header.colormap_length = fgetLittleShort(fin);
    targa_header.colormap_size = fgetc(fin);
    targa_header.x_origin = fgetLittleShort(fin);
    targa_header.y_origin = fgetLittleShort(fin);
    targa_header.width = fgetLittleShort(fin);
    targa_header.height = fgetLittleShort(fin);
    targa_header.pixel_size = fgetc(fin);
    targa_header.attributes = fgetc(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)
        fseek(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++) {
                unsigned char red,green,blue,alphabyte;
                switch (targa_header.pixel_size) {
                    case 24:
                            
                            blue = getc(fin);
                            green = getc(fin);
                            red = getc(fin);
                            *pixbuf++ = red;
                            *pixbuf++ = green;
                            *pixbuf++ = blue;
                            *pixbuf++ = 255;
                            break;
                    case 32:
                            blue = getc(fin);
                            green = getc(fin);
                            red = getc(fin);
                            alphabyte = getc(fin);
                            *pixbuf++ = red;
                            *pixbuf++ = green;
                            *pixbuf++ = blue;
                            *pixbuf++ = alphabyte;
                            break;
                }
            }
        }
    }
    else if (targa_header.image_type==10) {   // Runlength encoded RGB images
        unsigned char red,green,blue,alphabyte,packetHeader,packetSize,j;
        for(row=rows-1; row>=0; row--) {
            pixbuf = targa_rgba + row*columns*4;
            for(column=0; column<columns; ) {
                packetHeader=getc(fin);
                packetSize = 1 + (packetHeader & 0x7f);
                if (packetHeader & 0x80) {        // run-length packet
                    switch (targa_header.pixel_size) {
                        case 24:
                                blue = getc(fin);
                                green = getc(fin);
                                red = getc(fin);
                                alphabyte = 255;
                                break;
                        case 32:
                                blue = getc(fin);
                                green = getc(fin);
                                red = getc(fin);
                                alphabyte = getc(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 = getc(fin);
                                    green = getc(fin);
                                    red = getc(fin);
                                    *pixbuf++ = red;
                                    *pixbuf++ = green;
                                    *pixbuf++ = blue;
                                    *pixbuf++ = 255;
                                    break;
                            case 32:
                                    blue = getc(fin);
                                    green = getc(fin);
                                    red = getc(fin);
                                    alphabyte = getc(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:;
        }
    }
    
    fclose(fin);
}

/*
==================
R_LoadSkys
==================
*/
char    *suf[6] = {"rt", "bk", "lf", "ft", "up", "dn"};
void R_LoadSkys (void)
{
    int     i;
    FILE    *f;
    char    name[64];

    for (i=0 ; i<6 ; i++)
    {
        GL_Bind (SKY_TEX + i);
        sprintf (name, "gfx/env/bkgtst%s.tga", suf[i]);
        COM_FOpenFile (name, &f);
        if (!f)
        {
            Con_Printf ("Couldn't load %s\n", name);
            continue;
        }
        LoadTGA (f);
//      LoadPCX (f);

        glTexImage2DHelper (GL_TEXTURE_2D, 0, gl_solid_format, 256, 256, 0, GL_RGBA, GL_UNSIGNED_BYTE, targa_rgba);
//      glTexImage2DHelper (GL_TEXTURE_2D, 0, gl_solid_format, 256, 256, 0, GL_RGBA, GL_UNSIGNED_BYTE, pcx_rgb);

        free (targa_rgba);
//      free (pcx_rgb);

        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;

    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);
        }
    }
}


/*
==============
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, j, k;
    vec3_t  v;
    float   s, t;

#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
}


#endif

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

static texture_t* current_sky_mt;

/*
=============
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;
    // extern   int         skytexturenum;
    
    current_sky_mt = mt;

    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 );
    glTexImage2DHelper (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);
    glTexImage2DHelper (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);
}

void R_ReloadSky() {
    if (current_sky_mt) {
        R_InitSky(current_sky_mt);
    }
}
