/*
===========================================================================
Copyright (C) 1999-2005 Id Software, Inc.

This file is part of Quake III Arena source code.

Quake III Arena source code 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.

Quake III Arena source code 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 Quake III Arena source code; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
===========================================================================
*/
// tr_sky.c
#include "tr_local.h"

#define SKY_SUBDIVISIONS		8
#define HALF_SKY_SUBDIVISIONS	(SKY_SUBDIVISIONS/2)

static float s_cloudTexCoords[6][SKY_SUBDIVISIONS+1][SKY_SUBDIVISIONS+1][2];

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

POLYGON TO BOX SIDE PROJECTION

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

static const vec3_t sky_clip[6] =
{
	{ 1, 1, 0},
	{ 1,-1, 0},
	{ 0,-1, 1},
	{ 0, 1, 1},
	{ 1, 0, 1},
	{-1, 0, 1}
};

static float	sky_mins[2][6], sky_maxs[2][6];
static float	sky_min, sky_max;
static float	sky_min_depth;

/*
================
AddSkyPolygon
================
*/
static void AddSkyPolygon (int nump, vec3_t vecs) 
{
	int		i,j;
	vec3_t	v, av;
	float	s, t, dv;
	int		axis;
	float	*vp;
	// s = [0]/[2], t = [1]/[2]
	static const 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}
	};

	// 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];
		if (dv < 0.001)
			continue;	// don't divide by zero
		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 < sky_mins[0][axis])
			sky_mins[0][axis] = s;
		if (t < sky_mins[1][axis])
			sky_mins[1][axis] = t;
		if (s > sky_maxs[0][axis])
			sky_maxs[0][axis] = s;
		if (t > sky_maxs[1][axis])
			sky_maxs[1][axis] = t;
	}
}

#define	ON_EPSILON		0.1f			// point on plane side epsilon
#define	MAX_CLIP_VERTS	64
/*
================
ClipSkyPolygon
================
*/
static void ClipSkyPolygon (int nump, vec3_t vecs, int stage) 
{
	const 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)
		ri.Error (ERR_DROP, "ClipSkyPolygon: MAX_CLIP_VERTS");
	if (stage == 6)
	{	// fully clipped, so draw it
		AddSkyPolygon (nump, vecs);
		return;
	}

	front = back = qfalse;
	norm = sky_clip[stage];
	for (i=0, v = vecs ; i<nump ; i++, v+=3)
	{
		d = DotProduct (v, norm);
		if (d > ON_EPSILON)
		{
			front = qtrue;
			sides[i] = SIDE_FRONT;
		}
		else if (d < -ON_EPSILON)
		{
			back = qtrue;
			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);
}

/*
==============
ClearSkyBox
==============
*/
static void ClearSkyBox (void) {
	int		i;

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

/*
================
RB_ClipSkyPolygons
================
*/
static void RB_ClipSkyPolygons( const shaderCommands_t *input )
{
	vec3_t		p[5];	// need one extra point for clipping
	int			i, j;

	ClearSkyBox();

	for ( i = 0; i < input->numIndexes; i += 3 )
	{
		for (j = 0 ; j < 3 ; j++) 
		{
			VectorSubtract( input->xyz[input->indexes[i+j]],
							backEnd.viewParms.or.origin, 
							p[j] );
		}
		ClipSkyPolygon( 3, p[0], 0 );
	}
}

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

CLOUD VERTEX GENERATION

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

/*
** MakeSkyVec
**
** Parms: s, t range from -1 to 1
*/
static void MakeSkyVec( float s, float t, int axis, vec3_t outXYZ )
{
	// 1 = s, 2 = t, 3 = 2048
	static const 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
	};

	vec3_t		b;
	int			j, k;
	float	boxSize;

	boxSize = backEnd.viewParms.zFar / 1.75;		// div sqrt(3)
	b[0] = s*boxSize;
	b[1] = t*boxSize;
	b[2] = boxSize;

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


static const int sky_texorder[6] = {0, 2, 1, 3, 4, 5};
static vec3_t	s_skyPoints[SKY_SUBDIVISIONS+1][SKY_SUBDIVISIONS+1];
static float	s_skyTexCoords[SKY_SUBDIVISIONS+1][SKY_SUBDIVISIONS+1][2];


/*
=================
CullPoints
=================
*/
static qboolean CullPoints( vec4_t v[], const int count )
{
	const cplane_t *frust;
	int i, j;
	float dist;

	for ( i = 0; i < 5; i++ ) {
		frust = &backEnd.viewParms.frustum[i];
		for ( j = 0; j < count; j++ ) {
			dist = DotProduct( v[j], frust->normal ) - frust->dist;
			if ( dist >= 0 ) {
				break;
			}
		}
		// all points are completely behind at least of one frustum plane
		if ( j == count ) {
			return qtrue;
		}
	}

	return qfalse;
}


static qboolean CullSkySide( const int mins[2], const int maxs[2] )
{
	int s, t;
	vec4_t v[4];

	if ( r_nocull->integer )
		return qfalse;

	s = mins[0] + HALF_SKY_SUBDIVISIONS;
	t = mins[1] + HALF_SKY_SUBDIVISIONS;
	VectorAdd( s_skyPoints[t][s], backEnd.viewParms.or.origin, v[0] );

	s = mins[0] + HALF_SKY_SUBDIVISIONS;
	t = maxs[1] + HALF_SKY_SUBDIVISIONS;
	VectorAdd( s_skyPoints[t][s], backEnd.viewParms.or.origin, v[1] );

	s = maxs[0] + HALF_SKY_SUBDIVISIONS;
	t = mins[1] + HALF_SKY_SUBDIVISIONS;
	VectorAdd( s_skyPoints[t][s], backEnd.viewParms.or.origin, v[2] );

	s = maxs[0] + HALF_SKY_SUBDIVISIONS;
	t = maxs[1] + HALF_SKY_SUBDIVISIONS;
	VectorAdd( s_skyPoints[t][s], backEnd.viewParms.or.origin, v[3] );

	if ( CullPoints( v, 4 ) )
		return qtrue;

	return qfalse;
}


static void FillSkySide( const int mins[2], const int maxs[2], float skyTexCoords[SKY_SUBDIVISIONS+1][SKY_SUBDIVISIONS+1][2] )
{
	const int vertexStart = tess.numVertexes;
	const int tHeight = maxs[1] - mins[1] + 1;
	const int sWidth = maxs[0] - mins[0] + 1;
	int s, t;

	if ( CullSkySide( mins, maxs ) )
		return;

#if ( (SKY_SUBDIVISIONS+1) * (SKY_SUBDIVISIONS+1) * 6 > SHADER_MAX_VERTEXES )
	if ( tess.numVertexes + tHeight * sWidth > SHADER_MAX_VERTEXES )
		ri.Error( ERR_DROP, "SHADER_MAX_VERTEXES hit in %s()", __func__ );
#endif

#if ( SKY_SUBDIVISIONS * SKY_SUBDIVISIONS * 6 * 6 > SHADER_MAX_INDEXES )
	if ( tess.numIndexes + (tHeight - 1) * (sWidth - 1) * 6 > SHADER_MAX_INDEXES )
		ri.Error( ERR_DROP, "SHADER_MAX_INDEXES hit in %s()", __func__ );
#endif

	for ( t = mins[1]+HALF_SKY_SUBDIVISIONS; t <= maxs[1]+HALF_SKY_SUBDIVISIONS; t++ )
	{
		for ( s = mins[0]+HALF_SKY_SUBDIVISIONS; s <= maxs[0]+HALF_SKY_SUBDIVISIONS; s++ )
		{
			VectorAdd( s_skyPoints[t][s], backEnd.viewParms.or.origin, tess.xyz[ tess.numVertexes ] );
			tess.texCoords[0][tess.numVertexes][0] = skyTexCoords[t][s][0];
			tess.texCoords[0][tess.numVertexes][1] = skyTexCoords[t][s][1];
			tess.numVertexes++;
		}
	}

	for ( t = 0; t < tHeight-1; t++ )
	{	
		for ( s = 0; s < sWidth-1; s++ )
		{
			tess.indexes[tess.numIndexes] = vertexStart + s + t * ( sWidth );
			tess.numIndexes++;
			tess.indexes[tess.numIndexes] = vertexStart + s + ( t + 1 ) * ( sWidth );
			tess.numIndexes++;
			tess.indexes[tess.numIndexes] = vertexStart + s + 1 + t * ( sWidth );
			tess.numIndexes++;

			tess.indexes[tess.numIndexes] = vertexStart + s + ( t + 1 ) * ( sWidth );
			tess.numIndexes++;
			tess.indexes[tess.numIndexes] = vertexStart + s + 1 + ( t + 1 ) * ( sWidth );
			tess.numIndexes++;
			tess.indexes[tess.numIndexes] = vertexStart + s + 1 + t * ( sWidth );
			tess.numIndexes++;
		}
	}
}


static void DrawSkySide( image_t *image, const int mins[2], const int maxs[2] )
{
	tess.numVertexes = 0;
	tess.numIndexes = 0;

	FillSkySide( mins, maxs, s_skyTexCoords );

	if ( tess.numIndexes )
	{
		GL_Bind( image );
#ifdef USE_VULKAN
		tess.svars.texcoordPtr[0] = tess.texCoords[0];

		vk_bind_pipeline( vk.skybox_pipeline );
		vk_bind_index();
		vk_bind_geometry( TESS_XYZ | TESS_ST0 );
		vk_draw_geometry( r_showsky->integer ? DEPTH_RANGE_ZERO : DEPTH_RANGE_ONE, qtrue );
#else
		qglVertexPointer( 3, GL_FLOAT, 16, tess.xyz );
		qglTexCoordPointer( 2, GL_FLOAT, 0, tess.texCoords[0] );

		R_DrawElements( tess.numIndexes, tess.indexes );
#endif
		tess.numVertexes = 0;
		tess.numIndexes = 0;
	}
}


static void DrawSkyBox( const shader_t *shader )
{
	int		i;
	sky_min = 0;
	sky_max = 1;

	for ( i = 0; i < 6; i++ )
	{
		int sky_mins_subd[2], sky_maxs_subd[2];
		int s, t;

		sky_mins[0][i] = floor( sky_mins[0][i] * HALF_SKY_SUBDIVISIONS ) / HALF_SKY_SUBDIVISIONS;
		sky_mins[1][i] = floor( sky_mins[1][i] * HALF_SKY_SUBDIVISIONS ) / HALF_SKY_SUBDIVISIONS;
		sky_maxs[0][i] = ceil( sky_maxs[0][i] * HALF_SKY_SUBDIVISIONS ) / HALF_SKY_SUBDIVISIONS;
		sky_maxs[1][i] = ceil( sky_maxs[1][i] * HALF_SKY_SUBDIVISIONS ) / HALF_SKY_SUBDIVISIONS;

		if ( ( sky_mins[0][i] >= sky_maxs[0][i] ) || ( sky_mins[1][i] >= sky_maxs[1][i] ) )
		{
			continue;
		}

		sky_mins_subd[0] = sky_mins[0][i] * HALF_SKY_SUBDIVISIONS;
		sky_mins_subd[1] = sky_mins[1][i] * HALF_SKY_SUBDIVISIONS;
		sky_maxs_subd[0] = sky_maxs[0][i] * HALF_SKY_SUBDIVISIONS;
		sky_maxs_subd[1] = sky_maxs[1][i] * HALF_SKY_SUBDIVISIONS;

		if ( sky_mins_subd[0] < -HALF_SKY_SUBDIVISIONS ) 
			sky_mins_subd[0] = -HALF_SKY_SUBDIVISIONS;
		else if ( sky_mins_subd[0] > HALF_SKY_SUBDIVISIONS ) 
			sky_mins_subd[0] = HALF_SKY_SUBDIVISIONS;
		if ( sky_mins_subd[1] < -HALF_SKY_SUBDIVISIONS )
			sky_mins_subd[1] = -HALF_SKY_SUBDIVISIONS;
		else if ( sky_mins_subd[1] > HALF_SKY_SUBDIVISIONS ) 
			sky_mins_subd[1] = HALF_SKY_SUBDIVISIONS;

		if ( sky_maxs_subd[0] < -HALF_SKY_SUBDIVISIONS ) 
			sky_maxs_subd[0] = -HALF_SKY_SUBDIVISIONS;
		else if ( sky_maxs_subd[0] > HALF_SKY_SUBDIVISIONS ) 
			sky_maxs_subd[0] = HALF_SKY_SUBDIVISIONS;
		if ( sky_maxs_subd[1] < -HALF_SKY_SUBDIVISIONS ) 
			sky_maxs_subd[1] = -HALF_SKY_SUBDIVISIONS;
		else if ( sky_maxs_subd[1] > HALF_SKY_SUBDIVISIONS ) 
			sky_maxs_subd[1] = HALF_SKY_SUBDIVISIONS;

		//
		// iterate through the subdivisions
		//
		for ( t = sky_mins_subd[1]+HALF_SKY_SUBDIVISIONS; t <= sky_maxs_subd[1]+HALF_SKY_SUBDIVISIONS; t++ )
		{
			for ( s = sky_mins_subd[0]+HALF_SKY_SUBDIVISIONS; s <= sky_maxs_subd[0]+HALF_SKY_SUBDIVISIONS; s++ )
			{
				MakeSkyVec( ( s - HALF_SKY_SUBDIVISIONS ) / ( float ) HALF_SKY_SUBDIVISIONS, 
							( t - HALF_SKY_SUBDIVISIONS ) / ( float ) HALF_SKY_SUBDIVISIONS, 
							i,
							s_skyPoints[t][s] );
			}
		}

		DrawSkySide( shader->sky.outerbox[sky_texorder[i]], sky_mins_subd, sky_maxs_subd );
	}
}


static void FillCloudBox( void )
{
	int i;

	for ( i =0; i < 6; i++ )
	{
		int sky_mins_subd[2], sky_maxs_subd[2];
		int s, t;
		float MIN_T;

		if ( 1 ) // FIXME? shader->sky.fullClouds )
		{
			MIN_T = -HALF_SKY_SUBDIVISIONS;

			// still don't want to draw the bottom, even if fullClouds
			if ( i == 5 )
				continue;
		}
		else
		{
			switch( i )
			{
			case 0:
			case 1:
			case 2:
			case 3:
				MIN_T = -1;
				break;
			case 5:
				// don't draw clouds beneath you
				continue;
			case 4:		// top
			default:
				MIN_T = -HALF_SKY_SUBDIVISIONS;
				break;
			}
		}

		sky_mins[0][i] = floor( sky_mins[0][i] * HALF_SKY_SUBDIVISIONS ) / HALF_SKY_SUBDIVISIONS;
		sky_mins[1][i] = floor( sky_mins[1][i] * HALF_SKY_SUBDIVISIONS ) / HALF_SKY_SUBDIVISIONS;
		sky_maxs[0][i] = ceil( sky_maxs[0][i] * HALF_SKY_SUBDIVISIONS ) / HALF_SKY_SUBDIVISIONS;
		sky_maxs[1][i] = ceil( sky_maxs[1][i] * HALF_SKY_SUBDIVISIONS ) / HALF_SKY_SUBDIVISIONS;

		if ( ( sky_mins[0][i] >= sky_maxs[0][i] ) ||
			 ( sky_mins[1][i] >= sky_maxs[1][i] ) )
		{
			continue;
		}

		sky_mins_subd[0] = myftol( sky_mins[0][i] * HALF_SKY_SUBDIVISIONS );
		sky_mins_subd[1] = myftol( sky_mins[1][i] * HALF_SKY_SUBDIVISIONS );
		sky_maxs_subd[0] = myftol( sky_maxs[0][i] * HALF_SKY_SUBDIVISIONS );
		sky_maxs_subd[1] = myftol( sky_maxs[1][i] * HALF_SKY_SUBDIVISIONS );

		if ( sky_mins_subd[0] < -HALF_SKY_SUBDIVISIONS ) 
			sky_mins_subd[0] = -HALF_SKY_SUBDIVISIONS;
		else if ( sky_mins_subd[0] > HALF_SKY_SUBDIVISIONS ) 
			sky_mins_subd[0] = HALF_SKY_SUBDIVISIONS;
		if ( sky_mins_subd[1] < MIN_T )
			sky_mins_subd[1] = MIN_T;
		else if ( sky_mins_subd[1] > HALF_SKY_SUBDIVISIONS ) 
			sky_mins_subd[1] = HALF_SKY_SUBDIVISIONS;

		if ( sky_maxs_subd[0] < -HALF_SKY_SUBDIVISIONS ) 
			sky_maxs_subd[0] = -HALF_SKY_SUBDIVISIONS;
		else if ( sky_maxs_subd[0] > HALF_SKY_SUBDIVISIONS ) 
			sky_maxs_subd[0] = HALF_SKY_SUBDIVISIONS;
		if ( sky_maxs_subd[1] < MIN_T )
			sky_maxs_subd[1] = MIN_T;
		else if ( sky_maxs_subd[1] > HALF_SKY_SUBDIVISIONS ) 
			sky_maxs_subd[1] = HALF_SKY_SUBDIVISIONS;

		//
		// iterate through the subdivisions
		//
		for ( t = sky_mins_subd[1]+HALF_SKY_SUBDIVISIONS; t <= sky_maxs_subd[1]+HALF_SKY_SUBDIVISIONS; t++ )
		{
			for ( s = sky_mins_subd[0]+HALF_SKY_SUBDIVISIONS; s <= sky_maxs_subd[0]+HALF_SKY_SUBDIVISIONS; s++ )
			{
				MakeSkyVec( ( s - HALF_SKY_SUBDIVISIONS ) / ( float ) HALF_SKY_SUBDIVISIONS, 
							( t - HALF_SKY_SUBDIVISIONS ) / ( float ) HALF_SKY_SUBDIVISIONS, 
							i, 
							s_skyPoints[t][s] );
			}
		}

		FillSkySide( sky_mins_subd, sky_maxs_subd, s_cloudTexCoords[i] );
	}
}


/*
** R_BuildCloudData
*/
static void R_BuildCloudData( const shaderCommands_t *input )
{
	const shader_t *shader;

	shader = input->shader;

	sky_min = 1.0 / 256.0f;		// FIXME: not correct?
	sky_max = 255.0 / 256.0f;

	// set up for drawing
	tess.numIndexes = 0;
	tess.numVertexes = 0;

	if ( shader->sky.cloudHeight )
	{
		if ( tess.xstages[0] )
		{
			FillCloudBox();
		}
	}
}


static void BuildSkyTexCoords( void )
{
	float s, t;
	int i, j;

	for ( i = 0; i <= SKY_SUBDIVISIONS; i++ ) {
		for ( j = 0; j <= SKY_SUBDIVISIONS; j++ ) {
			s = ( j - HALF_SKY_SUBDIVISIONS ) / ( float ) HALF_SKY_SUBDIVISIONS;
			t = ( i - HALF_SKY_SUBDIVISIONS ) / ( float ) HALF_SKY_SUBDIVISIONS;

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

			if ( s < 0.0f )
			{
				s = 0.0f;
			}
			else if ( s > 1.0f )
			{
				s = 1.0f;
			}

			if ( t < 0.0f )
			{
				t = 0.0f;
			}
			else if ( t > 1.0f )
			{
				t = 1.0f;
			}

			t = 1.0f - t;

			s_skyTexCoords[i][j][0] = s;
			s_skyTexCoords[i][j][1] = t;
		}
	}
}


/*
** R_InitSkyTexCoords
** Called when a sky shader is parsed
*/
void R_InitSkyTexCoords( float heightCloud )
{
	int i, s, t;
	float radiusWorld = 4096;
	float p;
	float sRad, tRad;
	vec3_t skyVec;
	vec3_t v;

	if ( !Q_stricmp( glConfig.renderer_string, "GDI Generic" ) && !Q_stricmp( glConfig.version_string, "1.1.0" ) ) {
		// fix skybox rendering on MS software GL implementation
		sky_min_depth = 0.999f;
	} else {
		sky_min_depth = 1.0;
	}

	// init zfar so MakeSkyVec works even though
	// a world hasn't been bounded
	backEnd.viewParms.zFar = 1024;

	for ( i = 0; i < 6; i++ )
	{
		for ( t = 0; t <= SKY_SUBDIVISIONS; t++ )
		{
			for ( s = 0; s <= SKY_SUBDIVISIONS; s++ )
			{
				// compute vector from view origin to sky side integral point
				MakeSkyVec( ( s - HALF_SKY_SUBDIVISIONS ) / ( float ) HALF_SKY_SUBDIVISIONS, 
							( t - HALF_SKY_SUBDIVISIONS ) / ( float ) HALF_SKY_SUBDIVISIONS, 
							i,
							skyVec );

				// compute parametric value 'p' that intersects with cloud layer
				p = ( 1.0f / ( 2 * DotProduct( skyVec, skyVec ) ) ) *
					( -2 * skyVec[2] * radiusWorld + 
						2 * sqrt( Square( skyVec[2] ) * Square( radiusWorld ) + 
							2 * Square( skyVec[0] ) * radiusWorld * heightCloud +
							Square( skyVec[0] ) * Square( heightCloud ) + 
							2 * Square( skyVec[1] ) * radiusWorld * heightCloud +
							Square( skyVec[1] ) * Square( heightCloud ) + 
							2 * Square( skyVec[2] ) * radiusWorld * heightCloud +
							Square( skyVec[2] ) * Square( heightCloud ) ) );

				// compute intersection point based on p
				VectorScale( skyVec, p, v );
				v[2] += radiusWorld;

				// compute vector from world origin to intersection point 'v'
				VectorNormalize( v );

				sRad = Q_acos( v[0] );
				tRad = Q_acos( v[1] );

				s_cloudTexCoords[i][t][s][0] = sRad;
				s_cloudTexCoords[i][t][s][1] = tRad;
			}
		}
	}

	BuildSkyTexCoords();
}

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

/*
** RB_DrawSun
*/
void RB_DrawSun( float scale, shader_t *shader ) {
	float		size;
	float		dist;
	vec3_t		origin, vec1, vec2;
	color4ub_t	sunColor;

	if ( !backEnd.skyRenderedThisView )
		return;

	sunColor.u32 = ~0U;

#ifdef USE_VULKAN
	vk_update_mvp( NULL );
#else
	qglLoadMatrixf( backEnd.viewParms.world.modelMatrix );
#endif

	dist = backEnd.viewParms.zFar / 1.75;		// div sqrt(3)
	size = dist * scale;

	VectorMA( backEnd.viewParms.or.origin, dist, tr.sunDirection, origin );
	PerpendicularVector( vec1, tr.sunDirection );
	CrossProduct( tr.sunDirection, vec1, vec2 );

	VectorScale( vec1, size, vec1 );
	VectorScale( vec2, size, vec2 );

	// farthest depth range
#ifdef USE_VULKAN
	tess.depthRange = DEPTH_RANGE_ONE;
#else
	qglDepthRange( sky_min_depth, 1.0 );
#endif

	RB_BeginSurface( shader, 0 );

	RB_AddQuadStamp( origin, vec1, vec2, sunColor );

	RB_EndSurface();

	// back to normal depth range
#ifdef USE_VULKAN
	tess.depthRange = DEPTH_RANGE_NORMAL;
#else
	qglDepthRange( 0.0, 1.0 );
#endif
}


/*
================
RB_StageIteratorSky

All of the visible sky triangles are in tess

Other things could be stuck in here, like birds in the sky, etc
================
*/
void RB_StageIteratorSky( void ) {

#if defined (USE_VULKAN) && !defined (USE_BUFFER_CLEAR)
	if ( r_fastsky->integer && vk.clearAttachment ) {
#else
	if ( r_fastsky->integer ) {
#endif
		return;
	}

#ifdef USE_VBO
	VBO_UnBind();
#endif

	// go through all the polygons and project them onto
	// the sky box to see which blocks on each side need
	// to be drawn
	RB_ClipSkyPolygons( &tess );

	// r_showsky will let all the sky blocks be drawn in
	// front of everything to allow developers to see how
	// much sky is getting sucked in

#ifdef USE_VULKAN
	if ( r_showsky->integer ) {
		tess.depthRange = DEPTH_RANGE_ZERO;
	} else {
		tess.depthRange = DEPTH_RANGE_ONE;
	}
#else
	if ( r_showsky->integer ) {
		qglDepthRange( 0.0, 0.0 );
	} else {
		qglDepthRange( sky_min_depth, 1.0 );
	}
#endif

	// draw the outer skybox
	if ( tess.shader->sky.outerbox[0] && tess.shader->sky.outerbox[0] != tr.defaultImage ) {
#ifdef USE_VULKAN
		DrawSkyBox( tess.shader );
#else
		GL_ClientState( 1, CLS_NONE );
		GL_ClientState( 0, CLS_TEXCOORD_ARRAY );

		qglColor4f( tr.identityLight, tr.identityLight, tr.identityLight, 1.0 );

		GL_State( 0 );
		GL_Cull( CT_FRONT_SIDED );

		DrawSkyBox( tess.shader );
#endif
	}

	// generate the vertexes for all the clouds, which will be drawn
	// by the generic shader routine
	R_BuildCloudData( &tess );

	// draw the inner skybox
	if ( tess.numVertexes ) {
		RB_StageIteratorGeneric();
	}

	// back to normal depth range
#ifdef USE_VULKAN
	tess.depthRange = DEPTH_RANGE_NORMAL;
#else
	qglDepthRange( 0.0, 1.0 );
#endif

	// note that sky was drawn so we will draw a sun later
	backEnd.skyRenderedThisView = qtrue;
}
