src/mesa/tnl/t_vb_fog.c

   1 /*
   2  * Mesa 3-D graphics library
   3  *
   4  * Copyright (C) 1999-2006  Brian Paul   All Rights Reserved.
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a
   7  * copy of this software and associated documentation files (the "Software"),
   8  * to deal in the Software without restriction, including without limitation
   9  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  10  * and/or sell copies of the Software, and to permit persons to whom the
  11  * Software is furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included
  14  * in all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  17  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
  20  * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
  21  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  22  * OTHER DEALINGS IN THE SOFTWARE.
  23  *
  24  * Authors:
  25  *    Keith Whitwell <keithw@vmware.com>
  26  */
  27
  28
  29 #include "c99_math.h"
  30 #include "main/errors.h"
  31 #include "main/glheader.h"
  32 #include "main/macros.h"
  33
  34 #include "main/mtypes.h"
  35
  36 #include "math/m_xform.h"
  37
  38 #include "t_context.h"
  39 #include "t_pipeline.h"
  40
  41
  42 struct fog_stage_data {
  43    GLvector4f fogcoord;         /* has actual storage allocated */
  44 };
  45
  46 #define FOG_STAGE_DATA(stage) ((struct fog_stage_data *)stage->privatePtr)
  47
  48 #define FOG_EXP_TABLE_SIZE 256
  49 #define FOG_MAX (10.0F)
  50 #define EXP_FOG_MAX .0006595F
  51 #define FOG_INCR (FOG_MAX/FOG_EXP_TABLE_SIZE)
  52 static GLfloat exp_table[FOG_EXP_TABLE_SIZE];
  53 static GLfloat inited = 0;
  54
  55 #if 1
  56 #define NEG_EXP( result, narg )                                         \
  57 do {                                                                    \
  58    GLfloat f = (GLfloat) (narg * (1.0F / 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 static void
  77 init_static_data( 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] = expf(-f);
  83    }
  84    inited = 1;
  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 that fogcoords may be negative, if eye z is source absolute
  94  * value must be taken earlier.
  95  * Fog blend factors are in the range [0,1].
  96  */
  97 static void
  98 compute_fog_blend_factors(struct gl_context *ctx, GLvector4f *out, const GLvector4f *in)
  99 {
 100    GLfloat end  = ctx->Fog.End;
 101    GLfloat *v = in->start;
 102    GLuint stride = in->stride;
 103    GLuint n = in->count;
 104    GLfloat (*data)[4] = out->data;
 105    GLfloat d;
 106    GLuint i;
 107
 108    out->count = in->count;
 109
 110    switch (ctx->Fog.Mode) {
 111    case GL_LINEAR:
 112       if (ctx->Fog.Start == ctx->Fog.End)
 113          d = 1.0F;
 114       else
 115          d = 1.0F / (ctx->Fog.End - ctx->Fog.Start);
 116       for ( i = 0 ; i < n ; i++, STRIDE_F(v, stride)) {
 117          const GLfloat z = *v;
 118          GLfloat f = (end - z) * d;
 119          data[i][0] = CLAMP(f, 0.0F, 1.0F);
 120       }
 121       break;
 122    case GL_EXP:
 123       d = ctx->Fog.Density;
 124       for ( i = 0 ; i < n ; i++, STRIDE_F(v,stride)) {
 125          const GLfloat z = *v;
 126          NEG_EXP( data[i][0], d * z );
 127       }
 128       break;
 129    case GL_EXP2:
 130       d = ctx->Fog.Density*ctx->Fog.Density;
 131       for ( i = 0 ; i < n ; i++, STRIDE_F(v, stride)) {
 132          const GLfloat z = *v;
 133          NEG_EXP( data[i][0], d * z * z );
 134       }
 135       break;
 136    default:
 137       _mesa_problem(ctx, "Bad fog mode in make_fog_coord");
 138       return;
 139    }
 140 }
 141
 142
 143 static GLboolean
 144 run_fog_stage(struct gl_context *ctx, struct tnl_pipeline_stage *stage)
 145 {
 146    TNLcontext *tnl = TNL_CONTEXT(ctx);
 147    struct vertex_buffer *VB = &tnl->vb;
 148    struct fog_stage_data *store = FOG_STAGE_DATA(stage);
 149    GLvector4f *input;
 150
 151
 152    if (!ctx->Fog.Enabled)
 153       return GL_TRUE;
 154
 155    if (ctx->Fog.FogCoordinateSource == GL_FRAGMENT_DEPTH_EXT && !ctx->VertexProgram._Current) {
 156       GLuint i;
 157       GLfloat *coord;
 158       /* Fog is computed from vertex or fragment Z values */
 159       /* source = VB->AttribPtr[_TNL_ATTRIB_POS] or VB->EyePtr coords */
 160       /* dest = VB->AttribPtr[_TNL_ATTRIB_FOG] = fog stage private storage */
 161       VB->AttribPtr[_TNL_ATTRIB_FOG] = &store->fogcoord;
 162
 163       if (!ctx->_NeedEyeCoords) {
 164          /* compute fog coords from object coords */
 165          const GLfloat *m = ctx->ModelviewMatrixStack.Top->m;
 166          GLfloat plane[4];
 167
 168          /* Use this to store calculated eye z values:
 169           */
 170          input = &store->fogcoord;
 171
 172          plane[0] = m[2];
 173          plane[1] = m[6];
 174          plane[2] = m[10];
 175          plane[3] = m[14];
 176          /* Full eye coords weren't required, just calculate the
 177           * eye Z values.
 178           */
 179          _mesa_dotprod_tab[VB->AttribPtr[_TNL_ATTRIB_POS]->size]
 180             ( (GLfloat *) input->data,
 181               4 * sizeof(GLfloat),
 182               VB->AttribPtr[_TNL_ATTRIB_POS], plane );
 183
 184          input->count = VB->AttribPtr[_TNL_ATTRIB_POS]->count;
 185
 186          /* make sure coords are really positive
 187             NOTE should avoid going through array twice */
 188          coord = input->start;
 189          for (i = 0; i < input->count; i++) {
 190             *coord = fabsf(*coord);
 191             STRIDE_F(coord, input->stride);
 192          }
 193       }
 194       else {
 195          /* fog coordinates = eye Z coordinates - need to copy for ABS */
 196          input = &store->fogcoord;
 197
 198          if (VB->EyePtr->size < 2)
 199             _mesa_vector4f_clean_elem( VB->EyePtr, VB->Count, 2 );
 200
 201          input->stride = 4 * sizeof(GLfloat);
 202          input->count = VB->EyePtr->count;
 203          coord = VB->EyePtr->start;
 204          for (i = 0 ; i < VB->EyePtr->count; i++) {
 205             input->data[i][0] = fabsf(coord[2]);
 206             STRIDE_F(coord, VB->EyePtr->stride);
 207          }
 208       }
 209    }
 210    else {
 211       /* use glFogCoord() coordinates */
 212       input = VB->AttribPtr[_TNL_ATTRIB_FOG];  /* source data */
 213
 214       /* input->count may be one if glFogCoord was only called once
 215        * before glBegin.  But we need to compute fog for all vertices.
 216        */
 217       input->count = VB->AttribPtr[_TNL_ATTRIB_POS]->count;
 218
 219       VB->AttribPtr[_TNL_ATTRIB_FOG] = &store->fogcoord;  /* dest data */
 220    }
 221
 222    if (tnl->_DoVertexFog) {
 223       /* compute blend factors from fog coordinates */
 224       compute_fog_blend_factors( ctx, VB->AttribPtr[_TNL_ATTRIB_FOG], input );
 225    }
 226    else {
 227       /* results = incoming fog coords (compute fog per-fragment later) */
 228       VB->AttribPtr[_TNL_ATTRIB_FOG] = input;
 229    }
 230
 231    return GL_TRUE;
 232 }
 233
 234
 235
 236 /* Called the first time stage->run() is invoked.
 237  */
 238 static GLboolean
 239 alloc_fog_data(struct gl_context *ctx, struct tnl_pipeline_stage *stage)
 240 {
 241    TNLcontext *tnl = TNL_CONTEXT(ctx);
 242    struct fog_stage_data *store;
 243    stage->privatePtr = malloc(sizeof(*store));
 244    store = FOG_STAGE_DATA(stage);
 245    if (!store)
 246       return GL_FALSE;
 247
 248    _mesa_vector4f_alloc( &store->fogcoord, 0, tnl->vb.Size, 32 );
 249
 250    if (!inited)
 251       init_static_data();
 252
 253    return GL_TRUE;
 254 }
 255
 256
 257 static void
 258 free_fog_data(struct tnl_pipeline_stage *stage)
 259 {
 260    struct fog_stage_data *store = FOG_STAGE_DATA(stage);
 261    if (store) {
 262       _mesa_vector4f_free( &store->fogcoord );
 263       free( store );
 264       stage->privatePtr = NULL;
 265    }
 266 }
 267
 268
 269 const struct tnl_pipeline_stage _tnl_fog_coordinate_stage =
 270 {
 271    "build fog coordinates",     /* name */
 272    NULL,                        /* private_data */
 273    alloc_fog_data,              /* dtr */
 274    free_fog_data,               /* dtr */
 275    NULL,                /* check */
 276    run_fog_stage                /* run -- initially set to init. */
 277 };