/*
	gl_warp.c

	sky and water polygons

	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:

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

	$Id$
*/

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <string.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#ifdef HAVE_STRINGS_H
#include <strings.h>
#endif

#include "qtypes.h"
#include "console.h"
#include "model.h"
#include "quakefs.h"
#include "glquake.h"
#include "sys.h"

extern	double	realtime;
extern	model_t	*loadmodel;

extern	int		skytexturenum;
extern qboolean lighthalf;

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

// Set to true if a valid skybox is loaded --KB
qboolean	skyloaded = false;

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 = 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;

	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;
	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);

			VectorCopy (v, nv);
			nv[2] += r_waterripple->value
				* turbsin[(int)((v[3]*0.125+realtime) * TURBSCALE) & 255]
				* turbsin[(int)((v[4]*0.125+realtime) * TURBSCALE) & 255]
				* (1.0 / 64.0);
			
			glVertex3fv (nv);
		}
		glEnd ();
	}
}


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

  Quake 2 environment sky

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

#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;


TargaHeader		targa_header;
byte			*targa_rgba;

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

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

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

int fgetLittleLong (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)
{
	int				columns, rows, numPixels;
	byte			*pixbuf;
	int				row, column;
	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 = fgetLittleShort(fin);
	targa_header.colormap_length = fgetLittleShort(fin);
	targa_header.colormap_size = Qgetc(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 = 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);
}

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

	if (stricmp (skyname, "none") == 0)
	{
		skyloaded = false;
		return;
	}

	skyloaded = true;
	for (i=0 ; i<6 ; i++)
	{
		glBindTexture (GL_TEXTURE_2D, SKY_TEX + i);
                snprintf (name, sizeof(name),"env/%s%s.tga", skyname, suf[i]);
		COM_FOpenFile (name, &f);
		if (!f)
		{
			Con_DPrintf ("Couldn't load %s\n", name);
			skyloaded = false;
			continue;
		}
		LoadTGA (f);

		glTexImage2D (GL_TEXTURE_2D, 0, gl_solid_format, 256, 256, 0, GL_RGBA, GL_UNSIGNED_BYTE, targa_rgba);

		free (targa_rgba);

		glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
		glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	}
	if (!skyloaded)
		Con_Printf ("Unable to load skybox %s, using normal sky\n",
				skyname);
}

void
R_SkyBoxPolyVec(vec5_t v)
{
	// avoid interpolation seams
//	s = s * (254.0/256.0) + (1.0/256.0);
//	t = t * (254.0/256.0) + (1.0/256.0);
	glTexCoord2fv (v);
	glVertex3f (r_refdef.vieworg[0] + v[2],
			r_refdef.vieworg[1] + v[3],
			r_refdef.vieworg[2] + v[4]);
}

#define ftc(x) (x * (254.0/256.0) + (1.0/256.0))

vec5_t skyvec[6][4] = {
	{
		// right
		{ftc(1), ftc(0),  1024,  1024,  1024},
		{ftc(1), ftc(1),  1024,  1024, -1024},
		{ftc(0), ftc(1), -1024,  1024, -1024},
		{ftc(0), ftc(0), -1024,  1024,  1024}
	},
	{
		// back
		{ftc(1), ftc(0), -1024,  1024,  1024},
		{ftc(1), ftc(1), -1024,  1024, -1024},
		{ftc(0), ftc(1), -1024, -1024, -1024},
		{ftc(0), ftc(0), -1024, -1024,  1024}
	},
	{
		// left
		{ftc(1), ftc(0), -1024, -1024,  1024},
		{ftc(1), ftc(1), -1024, -1024, -1024},
		{ftc(0), ftc(1),  1024, -1024, -1024},
		{ftc(0), ftc(0),  1024, -1024,  1024}
	},
	{
		// front
		{ftc(1), ftc(0),  1024, -1024,  1024},
		{ftc(1), ftc(1),  1024, -1024, -1024},
		{ftc(0), ftc(1),  1024,  1024, -1024},
		{ftc(0), ftc(0),  1024,  1024,  1024}
	},
	{
		// up
		{ftc(1), ftc(0),  1024, -1024,  1024},
		{ftc(1), ftc(1),  1024,  1024,  1024},
		{ftc(0), ftc(1), -1024,  1024,  1024},
		{ftc(0), ftc(0), -1024, -1024,  1024}
	},
	{
		// down
		{ftc(1), ftc(0),  1024,  1024, -1024},
		{ftc(1), ftc(1),  1024, -1024, -1024},
		{ftc(0), ftc(1), -1024, -1024, -1024},
		{ftc(0), ftc(0), -1024,  1024, -1024}
	}
};

#undef ftc

void
R_DrawSkyBox (void)
{
	int			i, j;

	glEnable (GL_DEPTH_TEST);
	glDepthFunc (GL_ALWAYS);
//	glDisable (GL_BLEND);
//	glTexEnvf (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
	glDepthRange (gldepthmax, gldepthmax);
	if (lighthalf)
		glColor3f(0.5,0.5,0.5);
	else
		glColor3f(1,1,1);

	for (i = 0; i < 6; i++)
	{
		glBindTexture(GL_TEXTURE_2D, SKY_TEX + i);
		glBegin(GL_QUADS);
		for (j = 0; j < 4; j++)
			R_SkyBoxPolyVec(skyvec[i][j]);
		glEnd();
	}

	glColor3f (1,1,1);
	glDepthFunc (GL_LEQUAL);
	glEnable (GL_DEPTH_TEST);
	glDepthRange(gldepthmin, gldepthmax);
}


vec3_t domescale;
void
R_DrawSkyLayer (float s)
{
	int a, b;
	float x, y, a1x, a1y, a2x, a2y;
	vec3_t v;
	
	for (a = 0; a < 16; a++)
	{
		a1x = bubble_costable[a*2];
		a1y = -bubble_sintable[a*2];
		a2x = bubble_costable[(a+1)*2];
		a2y = -bubble_sintable[(a+1)*2];

		glBegin (GL_TRIANGLE_STRIP);
		glTexCoord2f(0.5 + s * (1.0 / 128.0), 0.5 + s * (1.0 / 128.0));
		glVertex3f(r_refdef.vieworg[0],
			   r_refdef.vieworg[1],
			   r_refdef.vieworg[2]+domescale[2]);
		for (b = 1; b < 8; b++)
		{
			x = bubble_costable[b*2+16];
			y = -bubble_sintable[b*2+16];

			v[0] = a1x*x * domescale[0];
			v[1] = a1y*x * domescale[1];
			v[2] =     y * domescale[2];
			glTexCoord2f((v[0] + s) * (1.0 / 128.0),
					(v[1] + s) * (1.0 / 128.0));
			glVertex3f(v[0] + r_refdef.vieworg[0],
					v[1] + r_refdef.vieworg[1],
					v[2] + r_refdef.vieworg[2]);

			v[0] = a2x*x * domescale[0];
			v[1] = a2y*x * domescale[1];
			v[2] =     y * domescale[2];
			glTexCoord2f((v[0] + s) * (1.0 / 128.0),
					(v[1] + s) * (1.0 / 128.0));
			glVertex3f(v[0] + r_refdef.vieworg[0],
					v[1] + r_refdef.vieworg[1],
					v[2] + r_refdef.vieworg[2]);
		}
		glTexCoord2f(0.5 + s * (1.0 / 128.0), 0.5 + s * (1.0 / 128.0));
		glVertex3f(r_refdef.vieworg[0],
			   r_refdef.vieworg[1],
			   r_refdef.vieworg[2]-domescale[2]);
		glEnd ();
	}
}


void
R_DrawSkyDome (void)
{
	glEnable (GL_DEPTH_TEST);
	glDepthFunc (GL_ALWAYS);
//	glDisable (GL_BLEND);
//	glTexEnvf (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
	glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
	glDepthRange (gldepthmax, gldepthmax);
	glDisable (GL_BLEND);
	if (lighthalf)
		glColor3f(0.5,0.5,0.5);
	else
		glColor3f(1,1,1);

	// base sky
	glBindTexture (GL_TEXTURE_2D, solidskytexture);
	domescale[0] = 512;
	domescale[1] = 512;
	domescale[2] = 128;
	speedscale = realtime*8;
	speedscale -= (int)speedscale & ~127;
	R_DrawSkyLayer (speedscale);
	glEnable (GL_BLEND);

	// clouds
	if (gl_skymultipass->value) {
		glBindTexture (GL_TEXTURE_2D, alphaskytexture);
		domescale[0] = 512;
		domescale[1] = 512;
		domescale[2] = 128;
		speedscale = realtime*16;
		speedscale -= (int)speedscale & ~127;
		R_DrawSkyLayer (speedscale);
	}

//	glDisable (GL_BLEND);
	glColor3f (1,1,1);
	glDepthFunc (GL_LEQUAL);
	glEnable (GL_DEPTH_TEST);
	glDepthRange (gldepthmin, gldepthmax);
}

void 
R_DrawSky ( void )
{
	if (skyloaded)
		R_DrawSkyBox();
	else
		R_DrawSkyDome();
}



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

/*
=============
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++;
	glBindTexture (GL_TEXTURE_2D, 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++;
	glBindTexture (GL_TEXTURE_2D, 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);
}

/*
=============
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 ();
	}
}

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

	// used when gl_texsort is on
	glBindTexture (GL_TEXTURE_2D, solidskytexture);
	speedscale = realtime*8;
	speedscale -= (int)speedscale & ~127 ;

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

	glEnable (GL_BLEND);
	glBindTexture (GL_TEXTURE_2D, alphaskytexture);
	speedscale = realtime*16;
	speedscale -= (int)speedscale & ~127 ;

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

	glDisable (GL_BLEND);
}

/*
===============
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)
{
	glBindTexture (GL_TEXTURE_2D, solidskytexture);
	speedscale = realtime*8;
	speedscale -= (int)speedscale & ~127 ;

	EmitSkyPolys (fa);

	glEnable (GL_BLEND);
	glBindTexture (GL_TEXTURE_2D, alphaskytexture);
	speedscale = realtime*16;
	speedscale -= (int)speedscale & ~127 ;

	EmitSkyPolys (fa);

	glDisable (GL_BLEND);
}