src/mesa/swrast/s_fog.c

   1 /* $Id: s_fog.c,v 1.23 2002/08/07 00:45:07 brianp Exp $ */
   2
   3 /*
   4  * Mesa 3-D graphics library
   5  * Version:  4.1
   6  *
   7  * Copyright (C) 1999-2002  Brian Paul   All Rights Reserved.
   8  *
   9  * Permission is hereby granted, free of charge, to any person obtaining a
  10  * copy of this software and associated documentation files (the "Software"),
  11  * to deal in the Software without restriction, including without limitation
  12  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  13  * and/or sell copies of the Software, and to permit persons to whom the
  14  * Software is furnished to do so, subject to the following conditions:
  15  *
  16  * The above copyright notice and this permission notice shall be included
  17  * in all copies or substantial portions of the Software.
  18  *
  19  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  20  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  21  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  22  * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
  23  * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  24  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  25  */
  26
  27
  28 #include "glheader.h"
  29 #include "colormac.h"
  30 #include "context.h"
  31 #include "macros.h"
  32 #include "mmath.h"
  33
  34 #include "s_context.h"
  35 #include "s_fog.h"
  36 #include "s_span.h"
  37
  38
  39
  40
  41 /**
  42  * Used to convert current raster distance to a fog factor in [0,1].
  43  */
  44 GLfloat
  45 _mesa_z_to_fogfactor(GLcontext *ctx, GLfloat z)
  46 {
  47    GLfloat d, f;
  48
  49    switch (ctx->Fog.Mode) {
  50    case GL_LINEAR:
  51       if (ctx->Fog.Start == ctx->Fog.End)
  52          d = 1.0F;
  53       else
  54          d = 1.0F / (ctx->Fog.End - ctx->Fog.Start);
  55       f = (ctx->Fog.End - z) * d;
  56       return CLAMP(f, 0.0F, 1.0F);
  57    case GL_EXP:
  58       d = ctx->Fog.Density;
  59       f = (GLfloat) exp(-d * z);
  60       return f;
  61    case GL_EXP2:
  62       d = ctx->Fog.Density;
  63       f = (GLfloat) exp(-(d * d * z * z));
  64       return f;
  65    default:
  66       _mesa_problem(ctx, "Bad fog mode in _mesa_z_to_fogfactor");
  67       return 0.0;
  68    }
  69 }
  70
  71
  72
  73 /**
  74  * Calculate fog factors (in [0,1]) from window z values
  75  * Input:  n - number of pixels
  76  *         z - array of integer depth values
  77  *         red, green, blue, alpha - pixel colors
  78  * Output:  red, green, blue, alpha - fogged pixel colors
  79  *
  80  * Use lookup table & interpolation?
  81  */
  82 static void
  83 compute_fog_factors_from_z( const GLcontext *ctx,
  84                             GLuint n,
  85                             const GLdepth z[],
  86                             GLfloat fogFact[] )
  87 {
  88    const GLfloat *proj = ctx->ProjectionMatrixStack.Top->m;
  89    const GLboolean ortho = (proj[15] != 0.0F);
  90    const GLfloat p10 = proj[10];
  91    const GLfloat p14 = proj[14];
  92    const GLfloat tz = ctx->Viewport._WindowMap.m[MAT_TZ];
  93    GLfloat szInv;
  94    GLuint i;
  95
  96    if (ctx->Viewport._WindowMap.m[MAT_SZ] == 0.0)
  97       szInv = 1.0F;
  98    else
  99       szInv = 1.0F / ctx->Viewport._WindowMap.m[MAT_SZ];
 100
 101    /*
 102     * Note: to compute eyeZ from the ndcZ we have to solve the following:
 103     *
 104     *        p[10] * eyeZ + p[14] * eyeW
 105     * ndcZ = ---------------------------
 106     *        p[11] * eyeZ + p[15] * eyeW
 107     *
 108     * Thus:
 109     *
 110     *        p[14] * eyeW - p[15] * eyeW * ndcZ
 111     * eyeZ = ----------------------------------
 112     *             p[11] * ndcZ - p[10]
 113     *
 114     * If we note:
 115     *    a) if using an orthographic projection, p[11] = 0 and p[15] = 1.
 116     *    b) if using a perspective projection, p[11] = -1 and p[15] = 0.
 117     *    c) we assume eyeW = 1 (not always true- glVertex4)
 118     *
 119     * Then we can simplify the calculation of eyeZ quite a bit.  We do
 120     * separate calculations for the orthographic and perspective cases below.
 121     * Note that we drop a negative sign or two since they don't matter.
 122     */
 123
 124    switch (ctx->Fog.Mode) {
 125       case GL_LINEAR:
 126          {
 127             GLfloat fogEnd = ctx->Fog.End;
 128             GLfloat fogScale;
 129             if (ctx->Fog.Start == ctx->Fog.End)
 130                fogScale = 1.0;
 131             else
 132                fogScale = 1.0F / (ctx->Fog.End - ctx->Fog.Start);
 133             if (ortho) {
 134                for (i=0;i<n;i++) {
 135                   GLfloat ndcz = ((GLfloat) z[i] - tz) * szInv;
 136                   GLfloat eyez = (ndcz - p14) / p10;
 137                   GLfloat f;
 138                   if (eyez < 0.0)
 139                      eyez = -eyez;
 140                   f = (fogEnd - eyez) * fogScale;
 141                   fogFact[i] = CLAMP(f, 0.0F, 1.0F);
 142                }
 143             }
 144             else {
 145                /* perspective */
 146                for (i=0;i<n;i++) {
 147                   GLfloat ndcz = ((GLfloat) z[i] - tz) * szInv;
 148                   GLfloat eyez = p14 / (ndcz + p10);
 149                   GLfloat f;
 150                   if (eyez < 0.0)
 151                      eyez = -eyez;
 152                   f = (fogEnd - eyez) * fogScale;
 153                   fogFact[i] = CLAMP(f, 0.0F, 1.0F);
 154                }
 155             }
 156          }
 157          break;
 158       case GL_EXP:
 159          if (ortho) {
 160             for (i=0;i<n;i++) {
 161                GLfloat ndcz = ((GLfloat) z[i] - tz) * szInv;
 162                GLfloat eyez = (ndcz - p14) / p10;
 163                if (eyez < 0.0)
 164                   eyez = -eyez;
 165                fogFact[i] = (GLfloat) exp( -ctx->Fog.Density * eyez );
 166             }
 167          }
 168          else {
 169             /* perspective */
 170             for (i=0;i<n;i++) {
 171                GLfloat ndcz = ((GLfloat) z[i] - tz) * szInv;
 172                GLfloat eyez = p14 / (ndcz + p10);
 173                if (eyez < 0.0)
 174                   eyez = -eyez;
 175                fogFact[i] = (GLfloat) exp( -ctx->Fog.Density * eyez );
 176             }
 177          }
 178          break;
 179       case GL_EXP2:
 180          {
 181             GLfloat negDensitySquared = -ctx->Fog.Density * ctx->Fog.Density;
 182             if (ortho) {
 183                for (i=0;i<n;i++) {
 184                   GLfloat ndcz = ((GLfloat) z[i] - tz) * szInv;
 185                   GLfloat eyez = (ndcz - p14) / p10;
 186                   GLfloat tmp = negDensitySquared * eyez * eyez;
 187 #if defined(__alpha__) || defined(__alpha)
 188                   /* XXX this underflow check may be needed for other systems*/
 189                   if (tmp < FLT_MIN_10_EXP)
 190                      tmp = FLT_MIN_10_EXP;
 191 #endif
 192                   fogFact[i] = (GLfloat) exp( tmp );
 193                }
 194             }
 195             else {
 196                /* perspective */
 197                for (i=0;i<n;i++) {
 198                   GLfloat ndcz = ((GLfloat) z[i] - tz) * szInv;
 199                   GLfloat eyez = p14 / (ndcz + p10);
 200                   GLfloat tmp = negDensitySquared * eyez * eyez;
 201 #if defined(__alpha__) || defined(__alpha)
 202                   /* XXX this underflow check may be needed for other systems*/
 203                   if (tmp < FLT_MIN_10_EXP)
 204                      tmp = FLT_MIN_10_EXP;
 205 #endif
 206                   fogFact[i] = (GLfloat) exp( tmp );
 207                }
 208             }
 209          }
 210          break;
 211       default:
 212          _mesa_problem(ctx, "Bad fog mode in compute_fog_factors_from_z");
 213          return;
 214    }
 215 }
 216
 217
 218
 219 /**
 220  * Apply fog to a span of RGBA pixels.
 221  * The fog factors are either in the span->array->fog or stored as base/step.
 222  * These are fog _factors_, not fog coords.  Fog coords were converted to
 223  * fog factors per vertex.
 224  */
 225 void
 226 _mesa_fog_rgba_span( const GLcontext *ctx, struct sw_span *span )
 227 {
 228    const SWcontext *swrast = SWRAST_CONTEXT(ctx);
 229    const GLuint n = span->end;
 230    GLchan (*rgba)[4] = (GLchan (*)[4]) span->array->rgba;
 231    GLchan rFog, gFog, bFog;
 232
 233    ASSERT(ctx->Fog.Enabled);
 234    ASSERT((span->interpMask | span->arrayMask) & SPAN_FOG);
 235    ASSERT(span->arrayMask & SPAN_RGBA);
 236
 237    UNCLAMPED_FLOAT_TO_CHAN(rFog, ctx->Fog.Color[RCOMP]);
 238    UNCLAMPED_FLOAT_TO_CHAN(gFog, ctx->Fog.Color[GCOMP]);
 239    UNCLAMPED_FLOAT_TO_CHAN(bFog, ctx->Fog.Color[BCOMP]);
 240
 241    if (swrast->_PreferPixelFog) {
 242       /* compute fog factor from each fragment's Z value */
 243       if ((span->interpMask & SPAN_Z) && (span->arrayMask & SPAN_Z) == 0)
 244          _mesa_span_interpolate_z(ctx, span);
 245       compute_fog_factors_from_z(ctx, n, span->array->z, span->array->fog);
 246       span->arrayMask |= SPAN_FOG;
 247    }
 248
 249    if (span->arrayMask & SPAN_FOG) {
 250       /* use fog array in span */
 251       GLuint i;
 252       for (i = 0; i < n; i++) {
 253          const GLfloat fog = span->array->fog[i];
 254          const GLfloat oneMinusFog = 1.0F - fog;
 255          rgba[i][RCOMP] = (GLchan) (fog * rgba[i][RCOMP] + oneMinusFog * rFog);
 256          rgba[i][GCOMP] = (GLchan) (fog * rgba[i][GCOMP] + oneMinusFog * gFog);
 257          rgba[i][BCOMP] = (GLchan) (fog * rgba[i][BCOMP] + oneMinusFog * bFog);
 258       }
 259    }
 260    else {
 261       /* interpolate fog factors */
 262       GLfloat fog = span->fog, dFog = span->fogStep;
 263       GLuint i;
 264       for (i = 0; i < n; i++) {
 265          const GLfloat oneMinusFog = 1.0F - fog;
 266          rgba[i][RCOMP] = (GLchan) (fog * rgba[i][RCOMP] + oneMinusFog * rFog);
 267          rgba[i][GCOMP] = (GLchan) (fog * rgba[i][GCOMP] + oneMinusFog * gFog);
 268          rgba[i][BCOMP] = (GLchan) (fog * rgba[i][BCOMP] + oneMinusFog * bFog);
 269          fog += dFog;
 270       }
 271    }
 272 }
 273
 274
 275 /**
 276  * As above, but color index mode.
 277  */
 278 void
 279 _mesa_fog_ci_span( const GLcontext *ctx, struct sw_span *span )
 280 {
 281    const SWcontext *swrast = SWRAST_CONTEXT(ctx);
 282    const GLuint n = span->end;
 283    GLuint *index = span->array->index;
 284
 285    ASSERT(ctx->Fog.Enabled);
 286    ASSERT(span->arrayMask & SPAN_INDEX);
 287    ASSERT((span->interpMask | span->arrayMask) & SPAN_FOG);
 288
 289    if (swrast->_PreferPixelFog) {
 290       /* compute fog factor from each fragment's Z value */
 291       if ((span->interpMask & SPAN_Z) && (span->arrayMask & SPAN_Z) == 0)
 292          _mesa_span_interpolate_z(ctx, span);
 293       compute_fog_factors_from_z(ctx, n, span->array->z, span->array->fog);
 294       span->arrayMask |= SPAN_FOG;
 295    }
 296
 297    if (span->arrayMask & SPAN_FOG) {
 298       const GLuint idx = (GLuint) ctx->Fog.Index;
 299       GLuint i;
 300       for (i = 0; i < n; i++) {
 301          const GLfloat f = CLAMP(span->array->fog[i], 0.0F, 1.0F);
 302          index[i] = (GLuint) ((GLfloat) index[i] + (1.0F - f) * idx);
 303       }
 304    }
 305    else {
 306       GLfloat fog = span->fog, dFog = span->fogStep;
 307       const GLuint idx = (GLuint) ctx->Fog.Index;
 308       GLuint i;
 309       for (i = 0; i < n; i++) {
 310          const GLfloat f = CLAMP(fog, 0.0F, 1.0F);
 311          index[i] = (GLuint) ((GLfloat) index[i] + (1.0F - f) * idx);
 312          fog += dFog;
 313       }
 314    }
 315 }