src/mesa/swrast/s_fog.c

   1 /* $Id: s_fog.c,v 1.25 2003/03/25 02:23:46 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
  33 #include "s_context.h"
  34 #include "s_fog.h"
  35 #include "s_span.h"
  36
  37
  38
  39
  40 /**
  41  * Used to convert current raster distance to a fog factor in [0,1].
  42  */
  43 GLfloat
  44 _swrast_z_to_fogfactor(GLcontext *ctx, GLfloat z)
  45 {
  46    GLfloat d, f;
  47
  48    switch (ctx->Fog.Mode) {
  49    case GL_LINEAR:
  50       if (ctx->Fog.Start == ctx->Fog.End)
  51          d = 1.0F;
  52       else
  53          d = 1.0F / (ctx->Fog.End - ctx->Fog.Start);
  54       f = (ctx->Fog.End - z) * d;
  55       return CLAMP(f, 0.0F, 1.0F);
  56    case GL_EXP:
  57       d = ctx->Fog.Density;
  58       f = (GLfloat) exp(-d * z);
  59       return f;
  60    case GL_EXP2:
  61       d = ctx->Fog.Density;
  62       f = (GLfloat) exp(-(d * d * z * z));
  63       return f;
  64    default:
  65       _mesa_problem(ctx, "Bad fog mode in _swrast_z_to_fogfactor");
  66       return 0.0;
  67    }
  68 }
  69
  70
  71
  72 /**
  73  * Calculate fog factors (in [0,1]) from window z values
  74  * Input:  n - number of pixels
  75  *         z - array of integer depth values
  76  *         red, green, blue, alpha - pixel colors
  77  * Output:  red, green, blue, alpha - fogged pixel colors
  78  *
  79  * Use lookup table & interpolation?
  80  */
  81 static void
  82 compute_fog_factors_from_z( const GLcontext *ctx,
  83                             GLuint n,
  84                             const GLdepth z[],
  85                             GLfloat fogFact[] )
  86 {
  87    const GLfloat *proj = ctx->ProjectionMatrixStack.Top->m;
  88    const GLboolean ortho = (proj[15] != 0.0F);
  89    const GLfloat p10 = proj[10];
  90    const GLfloat p14 = proj[14];
  91    const GLfloat tz = ctx->Viewport._WindowMap.m[MAT_TZ];
  92    GLfloat szInv;
  93    GLuint i;
  94
  95    if (ctx->Viewport._WindowMap.m[MAT_SZ] == 0.0)
  96       szInv = 1.0F;
  97    else
  98       szInv = 1.0F / ctx->Viewport._WindowMap.m[MAT_SZ];
  99
 100    /*
 101     * Note: to compute eyeZ from the ndcZ we have to solve the following:
 102     *
 103     *        p[10] * eyeZ + p[14] * eyeW
 104     * ndcZ = ---------------------------
 105     *        p[11] * eyeZ + p[15] * eyeW
 106     *
 107     * Thus:
 108     *
 109     *        p[14] * eyeW - p[15] * eyeW * ndcZ
 110     * eyeZ = ----------------------------------
 111     *             p[11] * ndcZ - p[10]
 112     *
 113     * If we note:
 114     *    a) if using an orthographic projection, p[11] = 0 and p[15] = 1.
 115     *    b) if using a perspective projection, p[11] = -1 and p[15] = 0.
 116     *    c) we assume eyeW = 1 (not always true- glVertex4)
 117     *
 118     * Then we can simplify the calculation of eyeZ quite a bit.  We do
 119     * separate calculations for the orthographic and perspective cases below.
 120     * Note that we drop a negative sign or two since they don't matter.
 121     */
 122
 123    switch (ctx->Fog.Mode) {
 124       case GL_LINEAR:
 125          {
 126             GLfloat fogEnd = ctx->Fog.End;
 127             GLfloat fogScale;
 128             if (ctx->Fog.Start == ctx->Fog.End)
 129                fogScale = 1.0;
 130             else
 131                fogScale = 1.0F / (ctx->Fog.End - ctx->Fog.Start);
 132             if (ortho) {
 133                for (i=0;i<n;i++) {
 134                   GLfloat ndcz = ((GLfloat) z[i] - tz) * szInv;
 135                   GLfloat eyez = (ndcz - p14) / p10;
 136                   GLfloat f;
 137                   if (eyez < 0.0)
 138                      eyez = -eyez;
 139                   f = (fogEnd - eyez) * fogScale;
 140                   fogFact[i] = CLAMP(f, 0.0F, 1.0F);
 141                }
 142             }
 143             else {
 144                /* perspective */
 145                for (i=0;i<n;i++) {
 146                   GLfloat ndcz = ((GLfloat) z[i] - tz) * szInv;
 147                   GLfloat eyez = p14 / (ndcz + p10);
 148                   GLfloat f;
 149                   if (eyez < 0.0)
 150                      eyez = -eyez;
 151                   f = (fogEnd - eyez) * fogScale;
 152                   fogFact[i] = CLAMP(f, 0.0F, 1.0F);
 153                }
 154             }
 155          }
 156          break;
 157       case GL_EXP:
 158          if (ortho) {
 159             for (i=0;i<n;i++) {
 160                GLfloat ndcz = ((GLfloat) z[i] - tz) * szInv;
 161                GLfloat eyez = (ndcz - p14) / p10;
 162                if (eyez < 0.0)
 163                   eyez = -eyez;
 164                fogFact[i] = (GLfloat) exp( -ctx->Fog.Density * eyez );
 165             }
 166          }
 167          else {
 168             /* perspective */
 169             for (i=0;i<n;i++) {
 170                GLfloat ndcz = ((GLfloat) z[i] - tz) * szInv;
 171                GLfloat eyez = p14 / (ndcz + p10);
 172                if (eyez < 0.0)
 173                   eyez = -eyez;
 174                fogFact[i] = (GLfloat) exp( -ctx->Fog.Density * eyez );
 175             }
 176          }
 177          break;
 178       case GL_EXP2:
 179          {
 180             GLfloat negDensitySquared = -ctx->Fog.Density * ctx->Fog.Density;
 181             if (ortho) {
 182                for (i=0;i<n;i++) {
 183                   GLfloat ndcz = ((GLfloat) z[i] - tz) * szInv;
 184                   GLfloat eyez = (ndcz - p14) / p10;
 185                   GLfloat tmp = negDensitySquared * eyez * eyez;
 186 #if defined(__alpha__) || defined(__alpha)
 187                   /* XXX this underflow check may be needed for other systems*/
 188                   if (tmp < FLT_MIN_10_EXP)
 189                      tmp = FLT_MIN_10_EXP;
 190 #endif
 191                   fogFact[i] = (GLfloat) exp( tmp );
 192                }
 193             }
 194             else {
 195                /* perspective */
 196                for (i=0;i<n;i++) {
 197                   GLfloat ndcz = ((GLfloat) z[i] - tz) * szInv;
 198                   GLfloat eyez = p14 / (ndcz + p10);
 199                   GLfloat tmp = negDensitySquared * eyez * eyez;
 200 #if defined(__alpha__) || defined(__alpha)
 201                   /* XXX this underflow check may be needed for other systems*/
 202                   if (tmp < FLT_MIN_10_EXP)
 203                      tmp = FLT_MIN_10_EXP;
 204 #endif
 205                   fogFact[i] = (GLfloat) exp( tmp );
 206                }
 207             }
 208          }
 209          break;
 210       default:
 211          _mesa_problem(ctx, "Bad fog mode in compute_fog_factors_from_z");
 212          return;
 213    }
 214 }
 215
 216
 217
 218 /**
 219  * Apply fog to a span of RGBA pixels.
 220  * The fog factors are either in the span->array->fog or stored as base/step.
 221  * These are fog _factors_, not fog coords.  Fog coords were converted to
 222  * fog factors per vertex.
 223  */
 224 void
 225 _swrast_fog_rgba_span( const GLcontext *ctx, struct sw_span *span )
 226 {
 227    const SWcontext *swrast = SWRAST_CONTEXT(ctx);
 228    const GLuint n = span->end;
 229    GLchan (*rgba)[4] = (GLchan (*)[4]) span->array->rgba;
 230    GLchan rFog, gFog, bFog;
 231
 232    ASSERT(ctx->Fog.Enabled);
 233    ASSERT((span->interpMask | span->arrayMask) & SPAN_FOG);
 234    ASSERT(span->arrayMask & SPAN_RGBA);
 235
 236    UNCLAMPED_FLOAT_TO_CHAN(rFog, ctx->Fog.Color[RCOMP]);
 237    UNCLAMPED_FLOAT_TO_CHAN(gFog, ctx->Fog.Color[GCOMP]);
 238    UNCLAMPED_FLOAT_TO_CHAN(bFog, ctx->Fog.Color[BCOMP]);
 239
 240    if (swrast->_PreferPixelFog) {
 241       /* compute fog factor from each fragment's Z value */
 242       if ((span->interpMask & SPAN_Z) && (span->arrayMask & SPAN_Z) == 0)
 243          _swrast_span_interpolate_z(ctx, span);
 244       compute_fog_factors_from_z(ctx, n, span->array->z, span->array->fog);
 245       span->arrayMask |= SPAN_FOG;
 246    }
 247
 248    if (span->arrayMask & SPAN_FOG) {
 249       /* use fog array in span */
 250       GLuint i;
 251       for (i = 0; i < n; i++) {
 252          const GLfloat fog = span->array->fog[i];
 253          const GLfloat oneMinusFog = 1.0F - fog;
 254          rgba[i][RCOMP] = (GLchan) (fog * rgba[i][RCOMP] + oneMinusFog * rFog);
 255          rgba[i][GCOMP] = (GLchan) (fog * rgba[i][GCOMP] + oneMinusFog * gFog);
 256          rgba[i][BCOMP] = (GLchan) (fog * rgba[i][BCOMP] + oneMinusFog * bFog);
 257       }
 258    }
 259    else {
 260       /* interpolate fog factors */
 261       GLfloat fog = span->fog, dFog = span->fogStep;
 262       GLuint i;
 263       for (i = 0; i < n; i++) {
 264          const GLfloat oneMinusFog = 1.0F - fog;
 265          rgba[i][RCOMP] = (GLchan) (fog * rgba[i][RCOMP] + oneMinusFog * rFog);
 266          rgba[i][GCOMP] = (GLchan) (fog * rgba[i][GCOMP] + oneMinusFog * gFog);
 267          rgba[i][BCOMP] = (GLchan) (fog * rgba[i][BCOMP] + oneMinusFog * bFog);
 268          fog += dFog;
 269       }
 270    }
 271 }
 272
 273
 274 /**
 275  * As above, but color index mode.
 276  */
 277 void
 278 _swrast_fog_ci_span( const GLcontext *ctx, struct sw_span *span )
 279 {
 280    const SWcontext *swrast = SWRAST_CONTEXT(ctx);
 281    const GLuint n = span->end;
 282    GLuint *index = span->array->index;
 283
 284    ASSERT(ctx->Fog.Enabled);
 285    ASSERT(span->arrayMask & SPAN_INDEX);
 286    ASSERT((span->interpMask | span->arrayMask) & SPAN_FOG);
 287
 288    if (swrast->_PreferPixelFog) {
 289       /* compute fog factor from each fragment's Z value */
 290       if ((span->interpMask & SPAN_Z) && (span->arrayMask & SPAN_Z) == 0)
 291          _swrast_span_interpolate_z(ctx, span);
 292       compute_fog_factors_from_z(ctx, n, span->array->z, span->array->fog);
 293       span->arrayMask |= SPAN_FOG;
 294    }
 295
 296    if (span->arrayMask & SPAN_FOG) {
 297       const GLuint idx = (GLuint) ctx->Fog.Index;
 298       GLuint i;
 299       for (i = 0; i < n; i++) {
 300          const GLfloat f = CLAMP(span->array->fog[i], 0.0F, 1.0F);
 301          index[i] = (GLuint) ((GLfloat) index[i] + (1.0F - f) * idx);
 302       }
 303    }
 304    else {
 305       GLfloat fog = span->fog, dFog = span->fogStep;
 306       const GLuint idx = (GLuint) ctx->Fog.Index;
 307       GLuint i;
 308       for (i = 0; i < n; i++) {
 309          const GLfloat f = CLAMP(fog, 0.0F, 1.0F);
 310          index[i] = (GLuint) ((GLfloat) index[i] + (1.0F - f) * idx);
 311          fog += dFog;
 312       }
 313    }
 314 }