src/mesa/drivers/dri/radeon/radeon_fog.c

   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@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