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      1 /**************************************************************************
      2 
      3 Copyright 2000, 2001 ATI Technologies Inc., Ontario, Canada, and
      4                      Tungsten Graphics Inc., Austin, Texas.
      5 
      6 All Rights Reserved.
      7 
      8 Permission is hereby granted, free of charge, to any person obtaining
      9 a copy of this software and associated documentation files (the
     10 "Software"), to deal in the Software without restriction, including
     11 without limitation the rights to use, copy, modify, merge, publish,
     12 distribute, sublicense, and/or sell copies of the Software, and to
     13 permit persons to whom the Software is furnished to do so, subject to
     14 the following conditions:
     15 
     16 The above copyright notice and this permission notice (including the
     17 next paragraph) shall be included in all copies or substantial
     18 portions of the Software.
     19 
     20 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
     21 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
     22 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
     23 IN NO EVENT SHALL THE COPYRIGHT OWNER(S) AND/OR ITS SUPPLIERS BE
     24 LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
     25 OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
     26 WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
     27 
     28 **************************************************************************/
     29 
     30 /*
     31  * Authors:
     32  *   Keith Whitwell <keith (at) tungstengraphics.com>
     33  */
     34 
     35 #include "main/glheader.h"
     36 #include "main/imports.h"
     37 #include "main/context.h"
     38 #include "main/mtypes.h"
     39 #include "main/enums.h"
     40 #include "main/macros.h"
     41 
     42 #include "radeon_fog.h"
     43 
     44 /**********************************************************************/
     45 /*             Fog blend factor computation for hw tcl                */
     46 /*             same calculation used as in t_vb_fog.c                 */
     47 /**********************************************************************/
     48 
     49 #define FOG_EXP_TABLE_SIZE 256
     50 #define FOG_MAX (10.0)
     51 #define EXP_FOG_MAX .0006595
     52 #define FOG_INCR (FOG_MAX/FOG_EXP_TABLE_SIZE)
     53 static GLfloat exp_table[FOG_EXP_TABLE_SIZE];
     54 
     55 #if 1
     56 #define NEG_EXP( result, narg )						\
     57 do {									\
     58    GLfloat f = (GLfloat) (narg * (1.0/FOG_INCR));			\
     59    GLint k = (GLint) f;							\
     60    if (k > FOG_EXP_TABLE_SIZE-2) 					\
     61       result = (GLfloat) EXP_FOG_MAX;					\
     62    else									\
     63       result = exp_table[k] + (f-k)*(exp_table[k+1]-exp_table[k]);	\
     64 } while (0)
     65 #else
     66 #define NEG_EXP( result, narg )					\
     67 do {								\
     68    result = exp(-narg);						\
     69 } while (0)
     70 #endif
     71 
     72 
     73 /**
     74  * Initialize the exp_table[] lookup table for approximating exp().
     75  */
     76 void
     77 radeonInitStaticFogData( void )
     78 {
     79    GLfloat f = 0.0F;
     80    GLint i = 0;
     81    for ( ; i < FOG_EXP_TABLE_SIZE ; i++, f += FOG_INCR) {
     82       exp_table[i] = (GLfloat) exp(-f);
     83    }
     84 }
     85 
     86 /**
     87  * Compute per-vertex fog blend factors from fog coordinates by
     88  * evaluating the GL_LINEAR, GL_EXP or GL_EXP2 fog function.
     89  * Fog coordinates are distances from the eye (typically between the
     90  * near and far clip plane distances).
     91  * Note the fog (eye Z) coords may be negative so we use ABS(z) below.
     92  * Fog blend factors are in the range [0,1].
     93  */
     94 float
     95 radeonComputeFogBlendFactor( struct gl_context *ctx, GLfloat fogcoord )
     96 {
     97 	GLfloat end  = ctx->Fog.End;
     98 	GLfloat d, temp;
     99 	const GLfloat z = FABSF(fogcoord);
    100 
    101 	switch (ctx->Fog.Mode) {
    102 	case GL_LINEAR:
    103 		if (ctx->Fog.Start == ctx->Fog.End)
    104 			d = 1.0F;
    105 		else
    106 			d = 1.0F / (ctx->Fog.End - ctx->Fog.Start);
    107 		temp = (end - z) * d;
    108 		return CLAMP(temp, 0.0F, 1.0F);
    109 		break;
    110 	case GL_EXP:
    111 		d = ctx->Fog.Density;
    112 		NEG_EXP( temp, d * z );
    113 		return temp;
    114 		break;
    115 	case GL_EXP2:
    116 		d = ctx->Fog.Density*ctx->Fog.Density;
    117 		NEG_EXP( temp, d * z * z );
    118 		return temp;
    119 		break;
    120 	default:
    121 		_mesa_problem(ctx, "Bad fog mode in make_fog_coord");
    122 		return 0;
    123 	}
    124 }
    125 
    126