src/mesa/swrast/s_accum.c

   1 /*
   2  * Mesa 3-D graphics library
   3  * Version:  6.5.2
   4  *
   5  * Copyright (C) 1999-2006  Brian Paul   All Rights Reserved.
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a
   8  * copy of this software and associated documentation files (the "Software"),
   9  * to deal in the Software without restriction, including without limitation
  10  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  11  * and/or sell copies of the Software, and to permit persons to whom the
  12  * Software is furnished to do so, subject to the following conditions:
  13  *
  14  * The above copyright notice and this permission notice shall be included
  15  * in all copies or substantial portions of the Software.
  16  *
  17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  18  * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  20  * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
  21  * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  22  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  23  */
  24
  25
  26 #include "main/glheader.h"
  27 #include "main/context.h"
  28 #include "main/macros.h"
  29 #include "main/imports.h"
  30 #include "fbobject.h"
  31
  32 #include "s_accum.h"
  33 #include "s_context.h"
  34 #include "s_masking.h"
  35 #include "s_span.h"
  36
  37
  38 /* XXX this would have to change for accum buffers with more or less
  39  * than 16 bits per color channel.
  40  */
  41 #define ACCUM_SCALE16 32767.0
  42
  43
  44 /*
  45  * Accumulation buffer notes
  46  *
  47  * Normally, accumulation buffer values are GLshorts with values in
  48  * [-32767, 32767] which represent floating point colors in [-1, 1],
  49  * as defined by the OpenGL specification.
  50  *
  51  * We optimize for the common case used for full-scene antialiasing:
  52  *    // start with accum buffer cleared to zero
  53  *    glAccum(GL_LOAD, w);   // or GL_ACCUM the first image
  54  *    glAccum(GL_ACCUM, w);
  55  *    ...
  56  *    glAccum(GL_ACCUM, w);
  57  *    glAccum(GL_RETURN, 1.0);
  58  * That is, we start with an empty accumulation buffer and accumulate
  59  * n images, each with weight w = 1/n.
  60  * In this scenario, we can simply store unscaled integer values in
  61  * the accum buffer instead of scaled integers.  We'll also keep track
  62  * of the w value so when we do GL_RETURN we simply divide the accumulated
  63  * values by n (n=1/w).
  64  * This lets us avoid _many_ int->float->int conversions.
  65  */
  66
  67
  68 #if CHAN_BITS == 8
  69 /* enable the optimization */
  70 #define USE_OPTIMIZED_ACCUM  1
  71 #else
  72 #define USE_OPTIMIZED_ACCUM  0
  73 #endif
  74
  75
  76 /**
  77  * This is called when we fall out of optimized/unscaled accum buffer mode.
  78  * That is, we convert each unscaled accum buffer value into a scaled value
  79  * representing the range[-1, 1].
  80  */
  81 static void
  82 rescale_accum( GLcontext *ctx )
  83 {
  84    SWcontext *swrast = SWRAST_CONTEXT(ctx);
  85    struct gl_renderbuffer *rb
  86       = ctx->DrawBuffer->Attachment[BUFFER_ACCUM].Renderbuffer;
  87    const GLfloat s = swrast->_IntegerAccumScaler * (32767.0F / CHAN_MAXF);
  88
  89    assert(rb);
  90    assert(rb->_BaseFormat == GL_RGBA);
  91    /* add other types in future? */
  92    assert(rb->DataType == GL_SHORT || rb->DataType == GL_UNSIGNED_SHORT);
  93    assert(swrast->_IntegerAccumMode);
  94
  95    if (rb->GetPointer(ctx, rb, 0, 0)) {
  96       /* directly-addressable memory */
  97       GLuint y;
  98       for (y = 0; y < rb->Height; y++) {
  99          GLuint i;
 100          GLshort *acc = (GLshort *) rb->GetPointer(ctx, rb, 0, y);
 101          for (i = 0; i < 4 * rb->Width; i++) {
 102             acc[i] = (GLshort) (acc[i] * s);
 103          }
 104       }
 105    }
 106    else {
 107       /* use get/put row funcs */
 108       GLuint y;
 109       for (y = 0; y < rb->Height; y++) {
 110          GLshort accRow[MAX_WIDTH * 4];
 111          GLuint i;
 112          rb->GetRow(ctx, rb, rb->Width, 0, y, accRow);
 113          for (i = 0; i < 4 * rb->Width; i++) {
 114             accRow[i] = (GLshort) (accRow[i] * s);
 115          }
 116          rb->PutRow(ctx, rb, rb->Width, 0, y, accRow, NULL);
 117       }
 118    }
 119
 120    swrast->_IntegerAccumMode = GL_FALSE;
 121 }
 122
 123
 124
 125 /**
 126  * Clear the accumulation Buffer.
 127  */
 128 void
 129 _swrast_clear_accum_buffer( GLcontext *ctx, struct gl_renderbuffer *rb )
 130 {
 131    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 132    GLuint x, y, width, height;
 133
 134    if (ctx->Visual.accumRedBits == 0) {
 135       /* No accumulation buffer! Not an error. */
 136       return;
 137    }
 138
 139    if (!rb || !rb->Data)
 140       return;
 141
 142    assert(rb->_BaseFormat == GL_RGBA);
 143    /* add other types in future? */
 144    assert(rb->DataType == GL_SHORT || rb->DataType == GL_UNSIGNED_SHORT);
 145
 146    /* bounds, with scissor */
 147    x = ctx->DrawBuffer->_Xmin;
 148    y = ctx->DrawBuffer->_Ymin;
 149    width = ctx->DrawBuffer->_Xmax - ctx->DrawBuffer->_Xmin;
 150    height = ctx->DrawBuffer->_Ymax - ctx->DrawBuffer->_Ymin;
 151
 152    if (rb->DataType == GL_SHORT || rb->DataType == GL_UNSIGNED_SHORT) {
 153       const GLfloat accScale = 32767.0;
 154       GLshort clearVal[4];
 155       GLuint i;
 156
 157       clearVal[0] = (GLshort) (ctx->Accum.ClearColor[0] * accScale);
 158       clearVal[1] = (GLshort) (ctx->Accum.ClearColor[1] * accScale);
 159       clearVal[2] = (GLshort) (ctx->Accum.ClearColor[2] * accScale);
 160       clearVal[3] = (GLshort) (ctx->Accum.ClearColor[3] * accScale);
 161
 162       for (i = 0; i < height; i++) {
 163          rb->PutMonoRow(ctx, rb, width, x, y + i, clearVal, NULL);
 164       }
 165    }
 166    else {
 167       /* someday support other sizes */
 168    }
 169
 170    /* update optimized accum state vars */
 171    if (ctx->Accum.ClearColor[0] == 0.0 && ctx->Accum.ClearColor[1] == 0.0 &&
 172        ctx->Accum.ClearColor[2] == 0.0 && ctx->Accum.ClearColor[3] == 0.0) {
 173 #if USE_OPTIMIZED_ACCUM
 174       swrast->_IntegerAccumMode = GL_TRUE;
 175 #else
 176       swrast->_IntegerAccumMode = GL_FALSE;
 177 #endif
 178       swrast->_IntegerAccumScaler = 0.0;  /* denotes empty accum buffer */
 179    }
 180    else {
 181       swrast->_IntegerAccumMode = GL_FALSE;
 182    }
 183 }
 184
 185
 186 static void
 187 accum_add(GLcontext *ctx, GLfloat value,
 188           GLint xpos, GLint ypos, GLint width, GLint height )
 189 {
 190    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 191    struct gl_renderbuffer *rb
 192       = ctx->DrawBuffer->Attachment[BUFFER_ACCUM].Renderbuffer;
 193
 194    assert(rb);
 195
 196    /* Leave optimized accum buffer mode */
 197    if (swrast->_IntegerAccumMode)
 198       rescale_accum(ctx);
 199
 200    if (rb->DataType == GL_SHORT || rb->DataType == GL_UNSIGNED_SHORT) {
 201       const GLshort incr = (GLshort) (value * ACCUM_SCALE16);
 202       if (rb->GetPointer(ctx, rb, 0, 0)) {
 203          GLint i, j;
 204          for (i = 0; i < height; i++) {
 205             GLshort *acc = (GLshort *) rb->GetPointer(ctx, rb, xpos, ypos + i);
 206             for (j = 0; j < 4 * width; j++) {
 207                acc[j] += incr;
 208             }
 209          }
 210       }
 211       else {
 212          GLint i, j;
 213          for (i = 0; i < height; i++) {
 214             GLshort accRow[4 * MAX_WIDTH];
 215             rb->GetRow(ctx, rb, width, xpos, ypos + i, accRow);
 216             for (j = 0; j < 4 * width; j++) {
 217                accRow[j] += incr;
 218             }
 219             rb->PutRow(ctx, rb, width, xpos, ypos + i, accRow, NULL);
 220          }
 221       }
 222    }
 223    else {
 224       /* other types someday */
 225    }
 226 }
 227
 228
 229 static void
 230 accum_mult(GLcontext *ctx, GLfloat mult,
 231            GLint xpos, GLint ypos, GLint width, GLint height )
 232 {
 233    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 234    struct gl_renderbuffer *rb
 235       = ctx->DrawBuffer->Attachment[BUFFER_ACCUM].Renderbuffer;
 236
 237    assert(rb);
 238
 239    /* Leave optimized accum buffer mode */
 240    if (swrast->_IntegerAccumMode)
 241       rescale_accum(ctx);
 242
 243    if (rb->DataType == GL_SHORT || rb->DataType == GL_UNSIGNED_SHORT) {
 244       if (rb->GetPointer(ctx, rb, 0, 0)) {
 245          GLint i, j;
 246          for (i = 0; i < height; i++) {
 247             GLshort *acc = (GLshort *) rb->GetPointer(ctx, rb, xpos, ypos + i);
 248             for (j = 0; j < 4 * width; j++) {
 249                acc[j] = (GLshort) (acc[j] * mult);
 250             }
 251          }
 252       }
 253       else {
 254          GLint i, j;
 255          for (i = 0; i < height; i++) {
 256             GLshort accRow[4 * MAX_WIDTH];
 257             rb->GetRow(ctx, rb, width, xpos, ypos + i, accRow);
 258             for (j = 0; j < 4 * width; j++) {
 259                accRow[j] = (GLshort) (accRow[j] * mult);
 260             }
 261             rb->PutRow(ctx, rb, width, xpos, ypos + i, accRow, NULL);
 262          }
 263       }
 264    }
 265    else {
 266       /* other types someday */
 267    }
 268 }
 269
 270
 271
 272 static void
 273 accum_accum(GLcontext *ctx, GLfloat value,
 274             GLint xpos, GLint ypos, GLint width, GLint height )
 275 {
 276    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 277    struct gl_renderbuffer *rb
 278       = ctx->DrawBuffer->Attachment[BUFFER_ACCUM].Renderbuffer;
 279    const GLboolean directAccess = (rb->GetPointer(ctx, rb, 0, 0) != NULL);
 280
 281    assert(rb);
 282
 283    if (!ctx->ReadBuffer->_ColorReadBuffer) {
 284       /* no read buffer - OK */
 285       return;
 286    }
 287
 288    /* May have to leave optimized accum buffer mode */
 289    if (swrast->_IntegerAccumScaler == 0.0 && value > 0.0 && value <= 1.0)
 290       swrast->_IntegerAccumScaler = value;
 291    if (swrast->_IntegerAccumMode && value != swrast->_IntegerAccumScaler)
 292       rescale_accum(ctx);
 293
 294    if (rb->DataType == GL_SHORT || rb->DataType == GL_UNSIGNED_SHORT) {
 295       const GLfloat scale = value * ACCUM_SCALE16 / CHAN_MAXF;
 296       GLshort accumRow[4 * MAX_WIDTH];
 297       GLchan rgba[MAX_WIDTH][4];
 298       GLint i;
 299
 300       for (i = 0; i < height; i++) {
 301          GLshort *acc;
 302          if (directAccess) {
 303             acc = (GLshort *) rb->GetPointer(ctx, rb, xpos, ypos + i);
 304          }
 305          else {
 306             rb->GetRow(ctx, rb, width, xpos, ypos + i, accumRow);
 307             acc = accumRow;
 308          }
 309
 310          /* read colors from color buffer */
 311          _swrast_read_rgba_span(ctx, ctx->ReadBuffer->_ColorReadBuffer, width,
 312                                 xpos, ypos + i, CHAN_TYPE, rgba);
 313
 314          /* do accumulation */
 315          if (swrast->_IntegerAccumMode) {
 316             /* simply add integer color values into accum buffer */
 317             GLint j;
 318             for (j = 0; j < width; j++) {
 319                acc[j * 4 + 0] += rgba[j][RCOMP];
 320                acc[j * 4 + 1] += rgba[j][GCOMP];
 321                acc[j * 4 + 2] += rgba[j][BCOMP];
 322                acc[j * 4 + 3] += rgba[j][ACOMP];
 323             }
 324          }
 325          else {
 326             /* scaled integer (or float) accum buffer */
 327             GLint j;
 328             for (j = 0; j < width; j++) {
 329                acc[j * 4 + 0] += (GLshort) ((GLfloat) rgba[j][RCOMP] * scale);
 330                acc[j * 4 + 1] += (GLshort) ((GLfloat) rgba[j][GCOMP] * scale);
 331                acc[j * 4 + 2] += (GLshort) ((GLfloat) rgba[j][BCOMP] * scale);
 332                acc[j * 4 + 3] += (GLshort) ((GLfloat) rgba[j][ACOMP] * scale);
 333             }
 334          }
 335
 336          if (!directAccess) {
 337             rb->PutRow(ctx, rb, width, xpos, ypos + i, accumRow, NULL);
 338          }
 339       }
 340    }
 341    else {
 342       /* other types someday */
 343    }
 344 }
 345
 346
 347
 348 static void
 349 accum_load(GLcontext *ctx, GLfloat value,
 350            GLint xpos, GLint ypos, GLint width, GLint height )
 351 {
 352    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 353    struct gl_renderbuffer *rb
 354       = ctx->DrawBuffer->Attachment[BUFFER_ACCUM].Renderbuffer;
 355    const GLboolean directAccess = (rb->GetPointer(ctx, rb, 0, 0) != NULL);
 356
 357    assert(rb);
 358
 359    if (!ctx->ReadBuffer->_ColorReadBuffer) {
 360       /* no read buffer - OK */
 361       return;
 362    }
 363
 364    /* This is a change to go into optimized accum buffer mode */
 365    if (value > 0.0 && value <= 1.0) {
 366 #if USE_OPTIMIZED_ACCUM
 367       swrast->_IntegerAccumMode = GL_TRUE;
 368 #else
 369       swrast->_IntegerAccumMode = GL_FALSE;
 370 #endif
 371       swrast->_IntegerAccumScaler = value;
 372    }
 373    else {
 374       swrast->_IntegerAccumMode = GL_FALSE;
 375       swrast->_IntegerAccumScaler = 0.0;
 376    }
 377
 378    if (rb->DataType == GL_SHORT || rb->DataType == GL_UNSIGNED_SHORT) {
 379       const GLfloat scale = value * ACCUM_SCALE16 / CHAN_MAXF;
 380       GLshort accumRow[4 * MAX_WIDTH];
 381       GLchan rgba[MAX_WIDTH][4];
 382       GLint i;
 383
 384       for (i = 0; i < height; i++) {
 385          GLshort *acc;
 386          if (directAccess) {
 387             acc = (GLshort *) rb->GetPointer(ctx, rb, xpos, ypos + i);
 388          }
 389          else {
 390             rb->GetRow(ctx, rb, width, xpos, ypos + i, accumRow);
 391             acc = accumRow;
 392          }
 393
 394          /* read colors from color buffer */
 395          _swrast_read_rgba_span(ctx, ctx->ReadBuffer->_ColorReadBuffer, width,
 396                                 xpos, ypos + i, CHAN_TYPE, rgba);
 397
 398          /* do load */
 399          if (swrast->_IntegerAccumMode) {
 400             /* just copy values in */
 401             GLint j;
 402             assert(swrast->_IntegerAccumScaler > 0.0);
 403             assert(swrast->_IntegerAccumScaler <= 1.0);
 404             for (j = 0; j < width; j++) {
 405                acc[j * 4 + 0] = rgba[j][RCOMP];
 406                acc[j * 4 + 1] = rgba[j][GCOMP];
 407                acc[j * 4 + 2] = rgba[j][BCOMP];
 408                acc[j * 4 + 3] = rgba[j][ACOMP];
 409             }
 410          }
 411          else {
 412             /* scaled integer (or float) accum buffer */
 413             GLint j;
 414             for (j = 0; j < width; j++) {
 415                acc[j * 4 + 0] = (GLshort) ((GLfloat) rgba[j][RCOMP] * scale);
 416                acc[j * 4 + 1] = (GLshort) ((GLfloat) rgba[j][GCOMP] * scale);
 417                acc[j * 4 + 2] = (GLshort) ((GLfloat) rgba[j][BCOMP] * scale);
 418                acc[j * 4 + 3] = (GLshort) ((GLfloat) rgba[j][ACOMP] * scale);
 419             }
 420          }
 421
 422          if (!directAccess) {
 423             rb->PutRow(ctx, rb, width, xpos, ypos + i, accumRow, NULL);
 424          }
 425       }
 426    }
 427 }
 428
 429
 430 static void
 431 accum_return(GLcontext *ctx, GLfloat value,
 432              GLint xpos, GLint ypos, GLint width, GLint height )
 433 {
 434    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 435    struct gl_framebuffer *fb = ctx->DrawBuffer;
 436    struct gl_renderbuffer *accumRb = fb->Attachment[BUFFER_ACCUM].Renderbuffer;
 437    const GLboolean directAccess
 438       = (accumRb->GetPointer(ctx, accumRb, 0, 0) != NULL);
 439    const GLboolean masking = (!ctx->Color.ColorMask[RCOMP] ||
 440                               !ctx->Color.ColorMask[GCOMP] ||
 441                               !ctx->Color.ColorMask[BCOMP] ||
 442                               !ctx->Color.ColorMask[ACOMP]);
 443
 444    static GLchan multTable[32768];
 445    static GLfloat prevMult = 0.0;
 446    const GLfloat mult = swrast->_IntegerAccumScaler;
 447    const GLint max = MIN2((GLint) (256 / mult), 32767);
 448
 449    /* May have to leave optimized accum buffer mode */
 450    if (swrast->_IntegerAccumMode && value != 1.0)
 451       rescale_accum(ctx);
 452
 453    if (swrast->_IntegerAccumMode && swrast->_IntegerAccumScaler > 0) {
 454       /* build lookup table to avoid many floating point multiplies */
 455       GLint j;
 456       assert(swrast->_IntegerAccumScaler <= 1.0);
 457       if (mult != prevMult) {
 458          for (j = 0; j < max; j++)
 459             multTable[j] = IROUND((GLfloat) j * mult);
 460          prevMult = mult;
 461       }
 462    }
 463
 464    if (accumRb->DataType == GL_SHORT ||
 465        accumRb->DataType == GL_UNSIGNED_SHORT) {
 466       const GLfloat scale = value * CHAN_MAXF / ACCUM_SCALE16;
 467       GLuint buffer;
 468       GLint i;
 469
 470       /* XXX maybe transpose the 'i' and 'buffer' loops??? */
 471       for (i = 0; i < height; i++) {
 472          GLshort accumRow[4 * MAX_WIDTH];
 473          GLshort *acc;
 474          SWspan span;
 475
 476          /* init color span */
 477          INIT_SPAN(span, GL_BITMAP);
 478          span.end = width;
 479          span.arrayMask = SPAN_RGBA;
 480          span.x = xpos;
 481          span.y = ypos + i;
 482
 483          if (directAccess) {
 484             acc = (GLshort *) accumRb->GetPointer(ctx, accumRb, xpos, ypos +i);
 485          }
 486          else {
 487             accumRb->GetRow(ctx, accumRb, width, xpos, ypos + i, accumRow);
 488             acc = accumRow;
 489          }
 490
 491          /* get the colors to return */
 492          if (swrast->_IntegerAccumMode) {
 493             GLint j;
 494             for (j = 0; j < width; j++) {
 495                ASSERT(acc[j * 4 + 0] < max);
 496                ASSERT(acc[j * 4 + 1] < max);
 497                ASSERT(acc[j * 4 + 2] < max);
 498                ASSERT(acc[j * 4 + 3] < max);
 499                span.array->rgba[j][RCOMP] = multTable[acc[j * 4 + 0]];
 500                span.array->rgba[j][GCOMP] = multTable[acc[j * 4 + 1]];
 501                span.array->rgba[j][BCOMP] = multTable[acc[j * 4 + 2]];
 502                span.array->rgba[j][ACOMP] = multTable[acc[j * 4 + 3]];
 503             }
 504          }
 505          else {
 506             /* scaled integer (or float) accum buffer */
 507             GLint j;
 508             for (j = 0; j < width; j++) {
 509 #if CHAN_BITS==32
 510                GLchan r = acc[j * 4 + 0] * scale;
 511                GLchan g = acc[j * 4 + 1] * scale;
 512                GLchan b = acc[j * 4 + 2] * scale;
 513                GLchan a = acc[j * 4 + 3] * scale;
 514 #else
 515                GLint r = IROUND( (GLfloat) (acc[j * 4 + 0]) * scale );
 516                GLint g = IROUND( (GLfloat) (acc[j * 4 + 1]) * scale );
 517                GLint b = IROUND( (GLfloat) (acc[j * 4 + 2]) * scale );
 518                GLint a = IROUND( (GLfloat) (acc[j * 4 + 3]) * scale );
 519 #endif
 520                span.array->rgba[j][RCOMP] = CLAMP( r, 0, CHAN_MAX );
 521                span.array->rgba[j][GCOMP] = CLAMP( g, 0, CHAN_MAX );
 522                span.array->rgba[j][BCOMP] = CLAMP( b, 0, CHAN_MAX );
 523                span.array->rgba[j][ACOMP] = CLAMP( a, 0, CHAN_MAX );
 524             }
 525          }
 526
 527          /* store colors */
 528          for (buffer = 0; buffer < fb->_NumColorDrawBuffers[0]; buffer++) {
 529             struct gl_renderbuffer *rb = fb->_ColorDrawBuffers[0][buffer];
 530             if (masking) {
 531                _swrast_mask_rgba_span(ctx, rb, &span);
 532             }
 533             rb->PutRow(ctx, rb, width, xpos, ypos + i, span.array->rgba, NULL);
 534          }
 535       }
 536    }
 537    else {
 538       /* other types someday */
 539    }
 540 }
 541
 542
 543
 544 /**
 545  * Software fallback for glAccum.
 546  */
 547 void
 548 _swrast_Accum(GLcontext *ctx, GLenum op, GLfloat value)
 549 {
 550    SWcontext *swrast = SWRAST_CONTEXT(ctx);
 551    GLint xpos, ypos, width, height;
 552
 553    if (SWRAST_CONTEXT(ctx)->NewState)
 554       _swrast_validate_derived( ctx );
 555
 556    if (!ctx->DrawBuffer->Attachment[BUFFER_ACCUM].Renderbuffer) {
 557       _mesa_warning(ctx, "Calling glAccum() without an accumulation buffer");
 558       return;
 559    }
 560
 561    RENDER_START(swrast, ctx);
 562
 563    /* Compute region after calling RENDER_START so that we know the
 564     * drawbuffer's size/bounds are up to date.
 565     */
 566    xpos = ctx->DrawBuffer->_Xmin;
 567    ypos = ctx->DrawBuffer->_Ymin;
 568    width =  ctx->DrawBuffer->_Xmax - ctx->DrawBuffer->_Xmin;
 569    height = ctx->DrawBuffer->_Ymax - ctx->DrawBuffer->_Ymin;
 570
 571    switch (op) {
 572       case GL_ADD:
 573          if (value != 0.0F) {
 574             accum_add(ctx, value, xpos, ypos, width, height);
 575          }
 576          break;
 577       case GL_MULT:
 578          if (value != 1.0F) {
 579             accum_mult(ctx, value, xpos, ypos, width, height);
 580          }
 581          break;
 582       case GL_ACCUM:
 583          if (value != 0.0F) {
 584             accum_accum(ctx, value, xpos, ypos, width, height);
 585          }
 586          break;
 587       case GL_LOAD:
 588          accum_load(ctx, value, xpos, ypos, width, height);
 589          break;
 590       case GL_RETURN:
 591          accum_return(ctx, value, xpos, ypos, width, height);
 592          break;
 593       default:
 594          _mesa_problem(ctx, "invalid mode in _swrast_Accum()");
 595          break;
 596    }
 597
 598    RENDER_FINISH(swrast, ctx);
 599 }