src/mesa/state_tracker/st_cb_fbo.c

   1 /**************************************************************************
   2  *
   3  * Copyright 2007 Tungsten Graphics, Inc., Cedar Park, Texas.
   4  * 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
   8  * "Software"), to deal in the Software without restriction, including
   9  * without limitation the rights to use, copy, modify, merge, publish,
  10  * distribute, sub license, and/or sell copies of the Software, and to
  11  * permit persons to whom the Software is furnished to do so, subject to
  12  * the following conditions:
  13  *
  14  * The above copyright notice and this permission notice (including the
  15  * next paragraph) shall be included in all copies or substantial portions
  16  * 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
  20  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
  21  * IN NO EVENT SHALL TUNGSTEN GRAPHICS AND/OR ITS SUPPLIERS BE LIABLE FOR
  22  * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  23  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  24  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  25  *
  26  **************************************************************************/
  27
  28
  29 /**
  30  * Framebuffer/renderbuffer functions.
  31  *
  32  * \author Brian Paul
  33  */
  34
  35
  36 #include "main/imports.h"
  37 #include "main/context.h"
  38 #include "main/fbobject.h"
  39 #include "main/framebuffer.h"
  40 #include "main/macros.h"
  41 #include "main/renderbuffer.h"
  42
  43 #include "pipe/p_context.h"
  44 #include "pipe/p_defines.h"
  45 #include "pipe/p_screen.h"
  46 #include "st_context.h"
  47 #include "st_cb_fbo.h"
  48 #include "st_format.h"
  49 #include "st_public.h"
  50 #include "st_texture.h"
  51
  52 #include "util/u_format.h"
  53 #include "util/u_rect.h"
  54 #include "util/u_inlines.h"
  55
  56
  57 /**
  58  * gl_renderbuffer::AllocStorage()
  59  * This is called to allocate the original drawing surface, and
  60  * during window resize.
  61  */
  62 static GLboolean
  63 st_renderbuffer_alloc_storage(GLcontext * ctx, struct gl_renderbuffer *rb,
  64                               GLenum internalFormat,
  65                               GLuint width, GLuint height)
  66 {
  67    struct pipe_screen *screen = ctx->st->pipe->screen;
  68    struct st_renderbuffer *strb = st_renderbuffer(rb);
  69    enum pipe_format format;
  70
  71    if (strb->format != PIPE_FORMAT_NONE)
  72       format = strb->format;
  73    else
  74       format = st_choose_renderbuffer_format(screen, internalFormat);
  75
  76    /* init renderbuffer fields */
  77    strb->Base.Width  = width;
  78    strb->Base.Height = height;
  79    strb->Base.Format = st_pipe_format_to_mesa_format(format);
  80    strb->Base.DataType = st_format_datatype(format);
  81
  82    strb->defined = GL_FALSE;  /* undefined contents now */
  83
  84    if (strb->software) {
  85       size_t size;
  86
  87       free(strb->data);
  88
  89       assert(strb->format != PIPE_FORMAT_NONE);
  90
  91       strb->stride = util_format_get_stride(strb->format, width);
  92       size = util_format_get_2d_size(strb->format, strb->stride, height);
  93
  94       strb->data = malloc(size);
  95
  96       return strb->data != NULL;
  97    }
  98    else {
  99       struct pipe_texture template;
 100       unsigned surface_usage;
 101
 102       /* Free the old surface and texture
 103        */
 104       pipe_surface_reference( &strb->surface, NULL );
 105       pipe_texture_reference( &strb->texture, NULL );
 106
 107       /* Setup new texture template.
 108        */
 109       memset(&template, 0, sizeof(template));
 110       template.target = PIPE_TEXTURE_2D;
 111       template.format = format;
 112       template.width0 = width;
 113       template.height0 = height;
 114       template.depth0 = 1;
 115       template.last_level = 0;
 116       template.nr_samples = rb->NumSamples;
 117       if (util_format_is_depth_or_stencil(format)) {
 118          template.tex_usage = PIPE_TEXTURE_USAGE_DEPTH_STENCIL;
 119       }
 120       else {
 121          template.tex_usage = (PIPE_TEXTURE_USAGE_DISPLAY_TARGET |
 122                                PIPE_TEXTURE_USAGE_RENDER_TARGET);
 123       }
 124
 125       /* Probably need dedicated flags for surface usage too:
 126        */
 127       surface_usage = (PIPE_BUFFER_USAGE_GPU_READ |
 128                        PIPE_BUFFER_USAGE_GPU_WRITE);
 129 #if 0
 130                        PIPE_BUFFER_USAGE_CPU_READ |
 131                        PIPE_BUFFER_USAGE_CPU_WRITE);
 132 #endif
 133
 134       strb->texture = screen->texture_create(screen, &template);
 135
 136       if (!strb->texture)
 137          return FALSE;
 138
 139       strb->surface = screen->get_tex_surface(screen,
 140                                               strb->texture,
 141                                               0, 0, 0,
 142                                               surface_usage);
 143       if (strb->surface) {
 144          assert(strb->surface->texture);
 145          assert(strb->surface->format);
 146          assert(strb->surface->width == width);
 147          assert(strb->surface->height == height);
 148       }
 149
 150       return strb->surface != NULL;
 151    }
 152 }
 153
 154
 155 /**
 156  * gl_renderbuffer::Delete()
 157  */
 158 static void
 159 st_renderbuffer_delete(struct gl_renderbuffer *rb)
 160 {
 161    struct st_renderbuffer *strb = st_renderbuffer(rb);
 162    ASSERT(strb);
 163    pipe_surface_reference(&strb->surface, NULL);
 164    pipe_texture_reference(&strb->texture, NULL);
 165    free(strb->data);
 166    free(strb);
 167 }
 168
 169
 170 /**
 171  * gl_renderbuffer::GetPointer()
 172  */
 173 static void *
 174 null_get_pointer(GLcontext * ctx, struct gl_renderbuffer *rb,
 175                  GLint x, GLint y)
 176 {
 177    /* By returning NULL we force all software rendering to go through
 178     * the span routines.
 179     */
 180 #if 0
 181    assert(0);  /* Should never get called with softpipe */
 182 #endif
 183    return NULL;
 184 }
 185
 186
 187 /**
 188  * Called via ctx->Driver.NewFramebuffer()
 189  */
 190 static struct gl_framebuffer *
 191 st_new_framebuffer(GLcontext *ctx, GLuint name)
 192 {
 193    /* XXX not sure we need to subclass gl_framebuffer for pipe */
 194    return _mesa_new_framebuffer(ctx, name);
 195 }
 196
 197
 198 /**
 199  * Called via ctx->Driver.NewRenderbuffer()
 200  */
 201 static struct gl_renderbuffer *
 202 st_new_renderbuffer(GLcontext *ctx, GLuint name)
 203 {
 204    struct st_renderbuffer *strb = ST_CALLOC_STRUCT(st_renderbuffer);
 205    if (strb) {
 206       _mesa_init_renderbuffer(&strb->Base, name);
 207       strb->Base.Delete = st_renderbuffer_delete;
 208       strb->Base.AllocStorage = st_renderbuffer_alloc_storage;
 209       strb->Base.GetPointer = null_get_pointer;
 210       strb->format = PIPE_FORMAT_NONE;
 211       return &strb->Base;
 212    }
 213    return NULL;
 214 }
 215
 216
 217 /**
 218  * Allocate a renderbuffer for a an on-screen window (not a user-created
 219  * renderbuffer).  The window system code determines the format.
 220  */
 221 struct gl_renderbuffer *
 222 st_new_renderbuffer_fb(enum pipe_format format, int samples, boolean sw)
 223 {
 224    struct st_renderbuffer *strb;
 225
 226    strb = ST_CALLOC_STRUCT(st_renderbuffer);
 227    if (!strb) {
 228       _mesa_error(NULL, GL_OUT_OF_MEMORY, "creating renderbuffer");
 229       return NULL;
 230    }
 231
 232    _mesa_init_renderbuffer(&strb->Base, 0);
 233    strb->Base.ClassID = 0x4242; /* just a unique value */
 234    strb->Base.NumSamples = samples;
 235    strb->Base.Format = st_pipe_format_to_mesa_format(format);
 236    strb->Base.DataType = st_format_datatype(format);
 237    strb->format = format;
 238    strb->software = sw;
 239
 240    switch (format) {
 241    case PIPE_FORMAT_A8R8G8B8_UNORM:
 242    case PIPE_FORMAT_B8G8R8A8_UNORM:
 243    case PIPE_FORMAT_X8R8G8B8_UNORM:
 244    case PIPE_FORMAT_B8G8R8X8_UNORM:
 245    case PIPE_FORMAT_A1R5G5B5_UNORM:
 246    case PIPE_FORMAT_A4R4G4B4_UNORM:
 247    case PIPE_FORMAT_R5G6B5_UNORM:
 248       strb->Base.InternalFormat = GL_RGBA;
 249       break;
 250    case PIPE_FORMAT_Z16_UNORM:
 251       strb->Base.InternalFormat = GL_DEPTH_COMPONENT16;
 252       break;
 253    case PIPE_FORMAT_Z32_UNORM:
 254       strb->Base.InternalFormat = GL_DEPTH_COMPONENT32;
 255       break;
 256    case PIPE_FORMAT_S8Z24_UNORM:
 257    case PIPE_FORMAT_Z24S8_UNORM:
 258    case PIPE_FORMAT_X8Z24_UNORM:
 259    case PIPE_FORMAT_Z24X8_UNORM:
 260       strb->Base.InternalFormat = GL_DEPTH24_STENCIL8_EXT;
 261       break;
 262    case PIPE_FORMAT_S8_UNORM:
 263       strb->Base.InternalFormat = GL_STENCIL_INDEX8_EXT;
 264       break;
 265    case PIPE_FORMAT_R16G16B16A16_SNORM:
 266       strb->Base.InternalFormat = GL_RGBA16;
 267       break;
 268    default:
 269       _mesa_problem(NULL,
 270                     "Unexpected format in st_new_renderbuffer_fb");
 271       free(strb);
 272       return NULL;
 273    }
 274
 275    /* st-specific methods */
 276    strb->Base.Delete = st_renderbuffer_delete;
 277    strb->Base.AllocStorage = st_renderbuffer_alloc_storage;
 278    strb->Base.GetPointer = null_get_pointer;
 279
 280    /* surface is allocated in st_renderbuffer_alloc_storage() */
 281    strb->surface = NULL;
 282
 283    return &strb->Base;
 284 }
 285
 286
 287
 288
 289 /**
 290  * Called via ctx->Driver.BindFramebufferEXT().
 291  */
 292 static void
 293 st_bind_framebuffer(GLcontext *ctx, GLenum target,
 294                     struct gl_framebuffer *fb, struct gl_framebuffer *fbread)
 295 {
 296
 297 }
 298
 299 /**
 300  * Called by ctx->Driver.FramebufferRenderbuffer
 301  */
 302 static void
 303 st_framebuffer_renderbuffer(GLcontext *ctx,
 304                             struct gl_framebuffer *fb,
 305                             GLenum attachment,
 306                             struct gl_renderbuffer *rb)
 307 {
 308    /* XXX no need for derivation? */
 309    _mesa_framebuffer_renderbuffer(ctx, fb, attachment, rb);
 310 }
 311
 312
 313 /**
 314  * Called by ctx->Driver.RenderTexture
 315  */
 316 static void
 317 st_render_texture(GLcontext *ctx,
 318                   struct gl_framebuffer *fb,
 319                   struct gl_renderbuffer_attachment *att)
 320 {
 321    struct pipe_screen *screen = ctx->st->pipe->screen;
 322    struct st_renderbuffer *strb;
 323    struct gl_renderbuffer *rb;
 324    struct pipe_texture *pt = st_get_texobj_texture(att->Texture);
 325    struct st_texture_object *stObj;
 326    const struct gl_texture_image *texImage;
 327    GLint pt_level;
 328
 329    /* When would this fail?  Perhaps assert? */
 330    if (!pt)
 331       return;
 332
 333    /* The first gallium texture level = Mesa BaseLevel */
 334    pt_level = MAX2(0, (GLint) att->TextureLevel - att->Texture->BaseLevel);
 335    texImage = att->Texture->Image[att->CubeMapFace][pt_level];
 336
 337    /* create new renderbuffer which wraps the texture image */
 338    rb = st_new_renderbuffer(ctx, 0);
 339    if (!rb) {
 340       _mesa_error(ctx, GL_OUT_OF_MEMORY, "glFramebufferTexture()");
 341       return;
 342    }
 343
 344    _mesa_reference_renderbuffer(&att->Renderbuffer, rb);
 345    assert(rb->RefCount == 1);
 346    rb->AllocStorage = NULL; /* should not get called */
 347    strb = st_renderbuffer(rb);
 348
 349    assert(strb->Base.RefCount > 0);
 350
 351    /* get the texture for the texture object */
 352    stObj = st_texture_object(att->Texture);
 353
 354    /* point renderbuffer at texobject */
 355    strb->rtt = stObj;
 356    strb->rtt_level = pt_level;
 357    strb->rtt_face = att->CubeMapFace;
 358    strb->rtt_slice = att->Zoffset;
 359
 360    rb->Width = texImage->Width2;
 361    rb->Height = texImage->Height2;
 362    rb->_BaseFormat = texImage->_BaseFormat;
 363    /*printf("***** render to texture level %d: %d x %d\n", att->TextureLevel, rb->Width, rb->Height);*/
 364
 365    /*printf("***** pipe texture %d x %d\n", pt->width0, pt->height0);*/
 366
 367    pipe_texture_reference( &strb->texture, pt );
 368
 369    pipe_surface_reference(&strb->surface, NULL);
 370
 371    assert(strb->rtt_level <= strb->texture->last_level);
 372
 373    /* new surface for rendering into the texture */
 374    strb->surface = screen->get_tex_surface(screen,
 375                                            strb->texture,
 376                                            strb->rtt_face,
 377                                            strb->rtt_level,
 378                                            strb->rtt_slice,
 379                                            PIPE_BUFFER_USAGE_GPU_READ |
 380                                            PIPE_BUFFER_USAGE_GPU_WRITE);
 381
 382    strb->Base.Format = st_pipe_format_to_mesa_format(pt->format);
 383    strb->Base.DataType = st_format_datatype(pt->format);
 384
 385    /*
 386    printf("RENDER TO TEXTURE obj=%p pt=%p surf=%p  %d x %d\n",
 387           att->Texture, pt, strb->surface, rb->Width, rb->Height);
 388    */
 389
 390    /* Invalidate buffer state so that the pipe's framebuffer state
 391     * gets updated.
 392     * That's where the new renderbuffer (which we just created) gets
 393     * passed to the pipe as a (color/depth) render target.
 394     */
 395    st_invalidate_state(ctx, _NEW_BUFFERS);
 396 }
 397
 398
 399 /**
 400  * Called via ctx->Driver.FinishRenderTexture.
 401  */
 402 static void
 403 st_finish_render_texture(GLcontext *ctx,
 404                          struct gl_renderbuffer_attachment *att)
 405 {
 406    struct st_renderbuffer *strb = st_renderbuffer(att->Renderbuffer);
 407
 408    if (!strb)
 409       return;
 410
 411    st_flush( ctx->st, PIPE_FLUSH_RENDER_CACHE, NULL );
 412
 413    if (strb->surface)
 414       pipe_surface_reference( &strb->surface, NULL );
 415
 416    strb->rtt = NULL;
 417
 418    /*
 419    printf("FINISH RENDER TO TEXTURE surf=%p\n", strb->surface);
 420    */
 421
 422    _mesa_reference_renderbuffer(&att->Renderbuffer, NULL);
 423
 424    /* restore previous framebuffer state */
 425    st_invalidate_state(ctx, _NEW_BUFFERS);
 426 }
 427
 428
 429 /**
 430  * Validate a renderbuffer attachment for a particular usage.
 431  */
 432
 433 static GLboolean
 434 st_validate_attachment(struct pipe_screen *screen,
 435                        const struct gl_renderbuffer_attachment *att,
 436                        GLuint usage)
 437 {
 438    const struct st_texture_object *stObj =
 439       st_texture_object(att->Texture);
 440
 441    /**
 442     * Only validate texture attachments for now, since
 443     * st_renderbuffer_alloc_storage makes sure that
 444     * the format is supported.
 445     */
 446
 447    if (att->Type != GL_TEXTURE)
 448       return GL_TRUE;
 449
 450    if (!stObj)
 451       return GL_FALSE;
 452
 453    return screen->is_format_supported(screen, stObj->pt->format,
 454                                       PIPE_TEXTURE_2D,
 455                                       usage, 0);
 456 }
 457
 458 /**
 459  * Check that the framebuffer configuration is valid in terms of what
 460  * the driver can support.
 461  *
 462  * For Gallium we only supports combined Z+stencil, not separate buffers.
 463  */
 464 static void
 465 st_validate_framebuffer(GLcontext *ctx, struct gl_framebuffer *fb)
 466 {
 467    struct pipe_screen *screen = ctx->st->pipe->screen;
 468    const struct gl_renderbuffer *depthRb =
 469       fb->Attachment[BUFFER_DEPTH].Renderbuffer;
 470    const struct gl_renderbuffer *stencilRb =
 471       fb->Attachment[BUFFER_STENCIL].Renderbuffer;
 472    GLuint i;
 473
 474    if (stencilRb && depthRb && stencilRb != depthRb) {
 475       fb->_Status = GL_FRAMEBUFFER_UNSUPPORTED_EXT;
 476       return;
 477    }
 478
 479    if (!st_validate_attachment(screen,
 480                                &fb->Attachment[BUFFER_DEPTH],
 481                                PIPE_TEXTURE_USAGE_DEPTH_STENCIL)) {
 482       fb->_Status = GL_FRAMEBUFFER_UNSUPPORTED_EXT;
 483       return;
 484    }
 485    if (!st_validate_attachment(screen,
 486                                &fb->Attachment[BUFFER_STENCIL],
 487                                PIPE_TEXTURE_USAGE_DEPTH_STENCIL)) {
 488       fb->_Status = GL_FRAMEBUFFER_UNSUPPORTED_EXT;
 489       return;
 490    }
 491    for (i = 0; i < ctx->Const.MaxColorAttachments; i++) {
 492       if (!st_validate_attachment(screen,
 493                                   &fb->Attachment[BUFFER_COLOR0 + i],
 494                                   PIPE_TEXTURE_USAGE_RENDER_TARGET)) {
 495          fb->_Status = GL_FRAMEBUFFER_UNSUPPORTED_EXT;
 496          return;
 497       }
 498    }
 499 }
 500
 501
 502 /**
 503  * Copy back color buffer to front color buffer.
 504  */
 505 static void
 506 copy_back_to_front(struct st_context *st,
 507                    struct gl_framebuffer *fb,
 508                    gl_buffer_index frontIndex,
 509                    gl_buffer_index backIndex)
 510
 511 {
 512    struct st_framebuffer *stfb = (struct st_framebuffer *) fb;
 513    struct pipe_surface *surf_front, *surf_back;
 514
 515    (void) st_get_framebuffer_surface(stfb, frontIndex, &surf_front);
 516    (void) st_get_framebuffer_surface(stfb, backIndex, &surf_back);
 517
 518    if (surf_front && surf_back) {
 519       if (st->pipe->surface_copy) {
 520          st->pipe->surface_copy(st->pipe,
 521                                 surf_front, 0, 0,  /* dest */
 522                                 surf_back, 0, 0,   /* src */
 523                                 fb->Width, fb->Height);
 524       } else {
 525          util_surface_copy(st->pipe, FALSE,
 526                            surf_front, 0, 0,
 527                            surf_back, 0, 0,
 528                            fb->Width, fb->Height);
 529       }
 530    }
 531 }
 532
 533
 534 /**
 535  * Check if we're drawing into, or read from, a front color buffer.  If the
 536  * front buffer is missing, create it now.
 537  *
 538  * The back color buffer must exist since we'll use its format/samples info
 539  * for creating the front buffer.
 540  *
 541  * \param frontIndex  either BUFFER_FRONT_LEFT or BUFFER_FRONT_RIGHT
 542  * \param backIndex  either BUFFER_BACK_LEFT or BUFFER_BACK_RIGHT
 543  */
 544 static void
 545 check_create_front_buffer(GLcontext *ctx, struct gl_framebuffer *fb,
 546                           gl_buffer_index frontIndex,
 547                           gl_buffer_index backIndex)
 548 {
 549    if (fb->Attachment[frontIndex].Renderbuffer == NULL) {
 550       GLboolean create = GL_FALSE;
 551
 552       /* check if drawing to or reading from front buffer */
 553       if (fb->_ColorReadBufferIndex == frontIndex) {
 554          create = GL_TRUE;
 555       }
 556       else {
 557          GLuint b;
 558          for (b = 0; b < fb->_NumColorDrawBuffers; b++) {
 559             if (fb->_ColorDrawBufferIndexes[b] == frontIndex) {
 560                create = GL_TRUE;
 561                break;
 562             }
 563          }
 564       }
 565
 566       if (create) {
 567          struct st_renderbuffer *back;
 568          struct gl_renderbuffer *front;
 569          enum pipe_format colorFormat;
 570          uint samples;
 571
 572          if (0)
 573             _mesa_debug(ctx, "Allocate new front buffer\n");
 574
 575          /* get back renderbuffer info */
 576          back = st_renderbuffer(fb->Attachment[backIndex].Renderbuffer);
 577          colorFormat = back->format;
 578          samples = back->Base.NumSamples;
 579
 580          /* create front renderbuffer */
 581          front = st_new_renderbuffer_fb(colorFormat, samples, FALSE);
 582          _mesa_add_renderbuffer(fb, frontIndex, front);
 583
 584          /* alloc texture/surface for new front buffer */
 585          front->AllocStorage(ctx, front, front->InternalFormat,
 586                              fb->Width, fb->Height);
 587
 588          /* initialize the front color buffer contents by copying
 589           * the back buffer.
 590           */
 591          copy_back_to_front(ctx->st, fb, frontIndex, backIndex);
 592       }
 593    }
 594 }
 595
 596
 597 /**
 598  * If front left/right color buffers are missing, create them now.
 599  */
 600 static void
 601 check_create_front_buffers(GLcontext *ctx, struct gl_framebuffer *fb)
 602 {
 603    /* check if we need to create the front left buffer now */
 604    check_create_front_buffer(ctx, fb, BUFFER_FRONT_LEFT, BUFFER_BACK_LEFT);
 605
 606    if (fb->Visual.stereoMode) {
 607       check_create_front_buffer(ctx, fb, BUFFER_FRONT_RIGHT, BUFFER_BACK_RIGHT);
 608    }
 609
 610    st_invalidate_state(ctx, _NEW_BUFFERS);
 611 }
 612
 613
 614 /**
 615  * Called via glDrawBuffer.
 616  */
 617 static void
 618 st_DrawBuffers(GLcontext *ctx, GLsizei count, const GLenum *buffers)
 619 {
 620    (void) count;
 621    (void) buffers;
 622    check_create_front_buffers(ctx, ctx->DrawBuffer);
 623 }
 624
 625
 626 /**
 627  * Called via glReadBuffer.
 628  */
 629 static void
 630 st_ReadBuffer(GLcontext *ctx, GLenum buffer)
 631 {
 632    (void) buffer;
 633    check_create_front_buffers(ctx, ctx->ReadBuffer);
 634 }
 635
 636
 637 void st_init_fbo_functions(struct dd_function_table *functions)
 638 {
 639    functions->NewFramebuffer = st_new_framebuffer;
 640    functions->NewRenderbuffer = st_new_renderbuffer;
 641    functions->BindFramebuffer = st_bind_framebuffer;
 642    functions->FramebufferRenderbuffer = st_framebuffer_renderbuffer;
 643    functions->RenderTexture = st_render_texture;
 644    functions->FinishRenderTexture = st_finish_render_texture;
 645    functions->ValidateFramebuffer = st_validate_framebuffer;
 646    /* no longer needed by core Mesa, drivers handle resizes...
 647    functions->ResizeBuffers = st_resize_buffers;
 648    */
 649
 650    functions->DrawBuffers = st_DrawBuffers;
 651    functions->ReadBuffer = st_ReadBuffer;
 652 }