src/mesa/swrast/s_fog.c

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