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      1 /**************************************************************************
      2 
      3 Copyright 2000, 2001 ATI Technologies Inc., Ontario, Canada, and
      4                      VMware, Inc.
      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 <keithw (at) vmware.com>
     33  */
     34 
     35 #include "c99_math.h"
     36 #include "main/glheader.h"
     37 #include "main/imports.h"
     38 #include "main/context.h"
     39 #include "main/mtypes.h"
     40 #include "main/enums.h"
     41 #include "main/macros.h"
     42 
     43 #include "radeon_screen.h"
     44 #include "radeon_fog.h"
     45 
     46 /**********************************************************************/
     47 /*             Fog blend factor computation for hw tcl                */
     48 /*             same calculation used as in t_vb_fog.c                 */
     49 /**********************************************************************/
     50 
     51 #define FOG_EXP_TABLE_SIZE 256
     52 #define FOG_MAX (10.0)
     53 #define EXP_FOG_MAX .0006595
     54 #define FOG_INCR (FOG_MAX/FOG_EXP_TABLE_SIZE)
     55 static GLfloat exp_table[FOG_EXP_TABLE_SIZE];
     56 
     57 #if 1
     58 #define NEG_EXP( result, narg )						\
     59 do {									\
     60    GLfloat f = (GLfloat) (narg * (1.0/FOG_INCR));			\
     61    GLint k = (GLint) f;							\
     62    if (k > FOG_EXP_TABLE_SIZE-2) 					\
     63       result = (GLfloat) EXP_FOG_MAX;					\
     64    else									\
     65       result = exp_table[k] + (f-k)*(exp_table[k+1]-exp_table[k]);	\
     66 } while (0)
     67 #else
     68 #define NEG_EXP( result, narg )					\
     69 do {								\
     70    result = exp(-narg);						\
     71 } while (0)
     72 #endif
     73 
     74 
     75 /**
     76  * Initialize the exp_table[] lookup table for approximating exp().
     77  */
     78 void
     79 radeonInitStaticFogData( void )
     80 {
     81    GLfloat f = 0.0F;
     82    GLint i = 0;
     83    for ( ; i < FOG_EXP_TABLE_SIZE ; i++, f += FOG_INCR) {
     84       exp_table[i] = (GLfloat) exp(-f);
     85    }
     86 }
     87 
     88 /**
     89  * Compute per-vertex fog blend factors from fog coordinates by
     90  * evaluating the GL_LINEAR, GL_EXP or GL_EXP2 fog function.
     91  * Fog coordinates are distances from the eye (typically between the
     92  * near and far clip plane distances).
     93  * Note the fog (eye Z) coords may be negative so we use ABS(z) below.
     94  * Fog blend factors are in the range [0,1].
     95  */
     96 float
     97 radeonComputeFogBlendFactor( struct gl_context *ctx, GLfloat fogcoord )
     98 {
     99 	GLfloat end  = ctx->Fog.End;
    100 	GLfloat d, temp;
    101 	const GLfloat z = fabsf(fogcoord);
    102 
    103 	switch (ctx->Fog.Mode) {
    104 	case GL_LINEAR:
    105 		if (ctx->Fog.Start == ctx->Fog.End)
    106 			d = 1.0F;
    107 		else
    108 			d = 1.0F / (ctx->Fog.End - ctx->Fog.Start);
    109 		temp = (end - z) * d;
    110 		return CLAMP(temp, 0.0F, 1.0F);
    111 		break;
    112 	case GL_EXP:
    113 		d = ctx->Fog.Density;
    114 		NEG_EXP( temp, d * z );
    115 		return temp;
    116 		break;
    117 	case GL_EXP2:
    118 		d = ctx->Fog.Density*ctx->Fog.Density;
    119 		NEG_EXP( temp, d * z * z );
    120 		return temp;
    121 		break;
    122 	default:
    123 		_mesa_problem(ctx, "Bad fog mode in make_fog_coord");
    124 		return 0;
    125 	}
    126 }
    127 
    128