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/*

 * Mesa 3-D graphics library

 * Version:  6.5

 *

 * Copyright (C) 1999-2006  Brian Paul   All Rights Reserved.

 *

 * Permission is hereby granted, free of charge, to any person obtaining a

 * copy of this software and associated documentation files (the "Software"),

 * to deal in the Software without restriction, including without limitation

 * the rights to use, copy, modify, merge, publish, distribute, sublicense,

 * and/or sell copies of the Software, and to permit persons to whom the

 * Software is furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included

 * in all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS

 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL

 * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN

 * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN

 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

 *

 * Authors:

 *    Keith Whitwell 

 */

#include "main/glheader.h"

#include "main/colormac.h"

#include "main/macros.h"

#include "main/imports.h"

#include "main/mtypes.h"

#include "math/m_xform.h"

#include "t_context.h"

#include "t_pipeline.h"

struct fog_stage_data {

   GLvector4f fogcoord;		/* has actual storage allocated */

};

#define FOG_STAGE_DATA(stage) ((struct fog_stage_data *)stage->privatePtr)

#define FOG_EXP_TABLE_SIZE 256

#define FOG_MAX (10.0)

#define EXP_FOG_MAX .0006595

#define FOG_INCR (FOG_MAX/FOG_EXP_TABLE_SIZE)

static GLfloat exp_table[FOG_EXP_TABLE_SIZE];

static GLfloat inited = 0;

#if 1

#define NEG_EXP( result, narg )						\

do {									\

   GLfloat f = (GLfloat) (narg * (1.0/FOG_INCR));			\

   GLint k = (GLint) f;							\

   if (k > FOG_EXP_TABLE_SIZE-2) 					\

      result = (GLfloat) EXP_FOG_MAX;					\

   else									\

      result = exp_table[k] + (f-k)*(exp_table[k+1]-exp_table[k]);	\

} while (0)

#else

#define NEG_EXP( result, narg )					\

do {								\

   result = exp(-narg);						\

} while (0)

#endif

/**

 * Initialize the exp_table[] lookup table for approximating exp().

 */

static void

init_static_data( void )

{

   GLfloat f = 0.0F;

   GLint i = 0;

   for ( ; i < FOG_EXP_TABLE_SIZE ; i++, f += FOG_INCR) {

      exp_table[i] = EXPF(-f);

   }

   inited = 1;

}

/**

 * Compute per-vertex fog blend factors from fog coordinates by

 * evaluating the GL_LINEAR, GL_EXP or GL_EXP2 fog function.

 * Fog coordinates are distances from the eye (typically between the

 * near and far clip plane distances).

 * Note that fogcoords may be negative, if eye z is source absolute

 * value must be taken earlier.

 * Fog blend factors are in the range [0,1].

 */

static void

compute_fog_blend_factors(struct gl_context *ctx, GLvector4f *out, const GLvector4f *in)

{

   GLfloat end  = ctx->Fog.End;

   GLfloat *v = in->start;

   GLuint stride = in->stride;

   GLuint n = in->count;

   GLfloat (*data)[4] = out->data;

   GLfloat d;

   GLuint i;

   out->count = in->count;

   switch (ctx->Fog.Mode) {

   case GL_LINEAR:

      if (ctx->Fog.Start == ctx->Fog.End)

         d = 1.0F;

      else

         d = 1.0F / (ctx->Fog.End - ctx->Fog.Start);

      for ( i = 0 ; i < n ; i++, STRIDE_F(v, stride)) {

         const GLfloat z = *v;

         GLfloat f = (end - z) * d;

	 data[i][0] = CLAMP(f, 0.0F, 1.0F);

      }

      break;

   case GL_EXP:

      d = ctx->Fog.Density;

      for ( i = 0 ; i < n ; i++, STRIDE_F(v,stride)) {

         const GLfloat z = *v;

         NEG_EXP( data[i][0], d * z );

      }

      break;

   case GL_EXP2:

      d = ctx->Fog.Density*ctx->Fog.Density;

      for ( i = 0 ; i < n ; i++, STRIDE_F(v, stride)) {

         const GLfloat z = *v;

         NEG_EXP( data[i][0], d * z * z );

      }

      break;

   default:

      _mesa_problem(ctx, "Bad fog mode in make_fog_coord");

      return;

   }

}

static GLboolean

run_fog_stage(struct gl_context *ctx, struct tnl_pipeline_stage *stage)

{

   TNLcontext *tnl = TNL_CONTEXT(ctx);

   struct vertex_buffer *VB = &tnl->vb;

   struct fog_stage_data *store = FOG_STAGE_DATA(stage);

   GLvector4f *input;

   if (!ctx->Fog.Enabled)

      return GL_TRUE;

   if (ctx->Fog.FogCoordinateSource == GL_FRAGMENT_DEPTH_EXT && !ctx->VertexProgram._Current) {

      GLuint i;

      GLfloat *coord;

      /* Fog is computed from vertex or fragment Z values */

      /* source = VB->AttribPtr[_TNL_ATTRIB_POS] or VB->EyePtr coords */

      /* dest = VB->AttribPtr[_TNL_ATTRIB_FOG] = fog stage private storage */

      VB->AttribPtr[_TNL_ATTRIB_FOG] = &store->fogcoord;

      if (!ctx->_NeedEyeCoords) {

         /* compute fog coords from object coords */

	 const GLfloat *m = ctx->ModelviewMatrixStack.Top->m;

	 GLfloat plane[4];

	 /* Use this to store calculated eye z values:

	  */

	 input = &store->fogcoord;

	 plane[0] = m[2];

	 plane[1] = m[6];

	 plane[2] = m[10];

	 plane[3] = m[14];

	 /* Full eye coords weren't required, just calculate the

	  * eye Z values.

	  */

	 _mesa_dotprod_tab[VB->AttribPtr[_TNL_ATTRIB_POS]->size]

	    ( (GLfloat *) input->data,

	      4 * sizeof(GLfloat),

	      VB->AttribPtr[_TNL_ATTRIB_POS], plane );

	 input->count = VB->AttribPtr[_TNL_ATTRIB_POS]->count;

	 /* make sure coords are really positive

	    NOTE should avoid going through array twice */

	 coord = input->start;

	 for (i = 0; i < input->count; i++) {

	    *coord = FABSF(*coord);

	    STRIDE_F(coord, input->stride);

	 }

      }

      else {

         /* fog coordinates = eye Z coordinates - need to copy for ABS */

	 input = &store->fogcoord;

	 if (VB->EyePtr->size < 2)

	    _mesa_vector4f_clean_elem( VB->EyePtr, VB->Count, 2 );

	 input->stride = 4 * sizeof(GLfloat);

	 input->count = VB->EyePtr->count;

	 coord = VB->EyePtr->start;

	 for (i = 0 ; i < VB->EyePtr->count; i++) {

	    input->data[i][0] = FABSF(coord[2]);

	    STRIDE_F(coord, VB->EyePtr->stride);

	 }

      }

   }

   else {

      /* use glFogCoord() coordinates */

      input = VB->AttribPtr[_TNL_ATTRIB_FOG];  /* source data */

      /* input->count may be one if glFogCoord was only called once

       * before glBegin.  But we need to compute fog for all vertices.

       */

      input->count = VB->AttribPtr[_TNL_ATTRIB_POS]->count;

      VB->AttribPtr[_TNL_ATTRIB_FOG] = &store->fogcoord;  /* dest data */

   }

   if (tnl->_DoVertexFog) {

      /* compute blend factors from fog coordinates */

      compute_fog_blend_factors( ctx, VB->AttribPtr[_TNL_ATTRIB_FOG], input );

   }

   else {

      /* results = incoming fog coords (compute fog per-fragment later) */

      VB->AttribPtr[_TNL_ATTRIB_FOG] = input;

   }

   return GL_TRUE;

}

/* Called the first time stage->run() is invoked.

 */

static GLboolean

alloc_fog_data(struct gl_context *ctx, struct tnl_pipeline_stage *stage)

{

   TNLcontext *tnl = TNL_CONTEXT(ctx);

   struct fog_stage_data *store;

   stage->privatePtr = MALLOC(sizeof(*store));

   store = FOG_STAGE_DATA(stage);

   if (!store)

      return GL_FALSE;

   _mesa_vector4f_alloc( &store->fogcoord, 0, tnl->vb.Size, 32 );

   if (!inited)

      init_static_data();

   return GL_TRUE;

}

static void

free_fog_data(struct tnl_pipeline_stage *stage)

{

   struct fog_stage_data *store = FOG_STAGE_DATA(stage);

   if (store) {

      _mesa_vector4f_free( &store->fogcoord );

      FREE( store );

      stage->privatePtr = NULL;

   }

}

const struct tnl_pipeline_stage _tnl_fog_coordinate_stage =

{

   "build fog coordinates",	/* name */

   NULL,			/* private_data */

   alloc_fog_data,		/* dtr */

   free_fog_data,		/* dtr */

   NULL,		/* check */

   run_fog_stage		/* run -- initially set to init. */

};