src/mesa/main/api_validate.c

   1 /*
   2  * Mesa 3-D graphics library
   3  * Version:  7.1
   4  *
   5  * Copyright (C) 1999-2007  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 #include <stdbool.h>
  26 #include "glheader.h"
  27 #include "api_validate.h"
  28 #include "bufferobj.h"
  29 #include "context.h"
  30 #include "imports.h"
  31 #include "mfeatures.h"
  32 #include "mtypes.h"
  33 #include "enums.h"
  34 #include "vbo/vbo.h"
  35 #include <stdbool.h>
  36
  37
  38 /**
  39  * \return  number of bytes in array [count] of type.
  40  */
  41 static GLsizei
  42 index_bytes(GLenum type, GLsizei count)
  43 {
  44    if (type == GL_UNSIGNED_INT) {
  45       return count * sizeof(GLuint);
  46    }
  47    else if (type == GL_UNSIGNED_BYTE) {
  48       return count * sizeof(GLubyte);
  49    }
  50    else {
  51       ASSERT(type == GL_UNSIGNED_SHORT);
  52       return count * sizeof(GLushort);
  53    }
  54 }
  55
  56
  57 /**
  58  * Find the max index in the given element/index buffer
  59  */
  60 GLuint
  61 _mesa_max_buffer_index(struct gl_context *ctx, GLuint count, GLenum type,
  62                        const void *indices,
  63                        struct gl_buffer_object *elementBuf)
  64 {
  65    const GLubyte *map = NULL;
  66    GLuint max = 0;
  67    GLuint i;
  68
  69    if (_mesa_is_bufferobj(elementBuf)) {
  70       /* elements are in a user-defined buffer object.  need to map it */
  71       map = ctx->Driver.MapBufferRange(ctx, 0, elementBuf->Size,
  72                                        GL_MAP_READ_BIT, elementBuf);
  73       /* Actual address is the sum of pointers */
  74       indices = (const GLvoid *) ADD_POINTERS(map, (const GLubyte *) indices);
  75    }
  76
  77    if (type == GL_UNSIGNED_INT) {
  78       for (i = 0; i < count; i++)
  79          if (((GLuint *) indices)[i] > max)
  80             max = ((GLuint *) indices)[i];
  81    }
  82    else if (type == GL_UNSIGNED_SHORT) {
  83       for (i = 0; i < count; i++)
  84          if (((GLushort *) indices)[i] > max)
  85             max = ((GLushort *) indices)[i];
  86    }
  87    else {
  88       ASSERT(type == GL_UNSIGNED_BYTE);
  89       for (i = 0; i < count; i++)
  90          if (((GLubyte *) indices)[i] > max)
  91             max = ((GLubyte *) indices)[i];
  92    }
  93
  94    if (map) {
  95       ctx->Driver.UnmapBuffer(ctx, elementBuf);
  96    }
  97
  98    return max;
  99 }
 100
 101
 102 /**
 103  * Check if OK to draw arrays/elements.
 104  */
 105 static GLboolean
 106 check_valid_to_render(struct gl_context *ctx, const char *function)
 107 {
 108    if (!_mesa_valid_to_render(ctx, function)) {
 109       return GL_FALSE;
 110    }
 111
 112    switch (ctx->API) {
 113    case API_OPENGLES2:
 114       /* For ES2, we can draw if any vertex array is enabled (and we
 115        * should always have a vertex program/shader). */
 116       if (ctx->Array.ArrayObj->_Enabled == 0x0 || !ctx->VertexProgram._Current)
 117          return GL_FALSE;
 118       break;
 119
 120    case API_OPENGLES:
 121       /* For OpenGL ES, only draw if we have vertex positions
 122        */
 123       if (!ctx->Array.ArrayObj->VertexAttrib[VERT_ATTRIB_POS].Enabled)
 124          return GL_FALSE;
 125       break;
 126
 127    case API_OPENGL_COMPAT:
 128    case API_OPENGL_CORE:
 129       {
 130          const struct gl_shader_program *vsProg =
 131             ctx->Shader.CurrentVertexProgram;
 132          GLboolean haveVertexShader = (vsProg && vsProg->LinkStatus);
 133          GLboolean haveVertexProgram = ctx->VertexProgram._Enabled;
 134          if (haveVertexShader || haveVertexProgram) {
 135             /* Draw regardless of whether or not we have any vertex arrays.
 136              * (Ex: could draw a point using a constant vertex pos)
 137              */
 138             return GL_TRUE;
 139          }
 140          else {
 141             /* Draw if we have vertex positions (GL_VERTEX_ARRAY or generic
 142              * array [0]).
 143              */
 144             return (ctx->Array.ArrayObj->VertexAttrib[VERT_ATTRIB_POS].Enabled ||
 145                     ctx->Array.ArrayObj->VertexAttrib[VERT_ATTRIB_GENERIC0].Enabled);
 146          }
 147       }
 148       break;
 149
 150    default:
 151       assert(!"Invalid API value in check_valid_to_render()");
 152    }
 153
 154    return GL_TRUE;
 155 }
 156
 157
 158 /**
 159  * Do bounds checking on array element indexes.  Check that the vertices
 160  * pointed to by the indices don't lie outside buffer object bounds.
 161  * \return GL_TRUE if OK, GL_FALSE if any indexed vertex goes is out of bounds
 162  */
 163 static GLboolean
 164 check_index_bounds(struct gl_context *ctx, GLsizei count, GLenum type,
 165                    const GLvoid *indices, GLint basevertex)
 166 {
 167    struct _mesa_prim prim;
 168    struct _mesa_index_buffer ib;
 169    GLuint min, max;
 170
 171    /* Only the X Server needs to do this -- otherwise, accessing outside
 172     * array/BO bounds allows application termination.
 173     */
 174    if (!ctx->Const.CheckArrayBounds)
 175       return GL_TRUE;
 176
 177    memset(&prim, 0, sizeof(prim));
 178    prim.count = count;
 179
 180    memset(&ib, 0, sizeof(ib));
 181    ib.type = type;
 182    ib.ptr = indices;
 183    ib.obj = ctx->Array.ArrayObj->ElementArrayBufferObj;
 184
 185    vbo_get_minmax_indices(ctx, &prim, &ib, &min, &max, 1);
 186
 187    if ((int)(min + basevertex) < 0 ||
 188        max + basevertex >= ctx->Array.ArrayObj->_MaxElement) {
 189       /* the max element is out of bounds of one or more enabled arrays */
 190       _mesa_warning(ctx, "glDrawElements() index=%u is out of bounds (max=%u)",
 191                     max, ctx->Array.ArrayObj->_MaxElement);
 192       return GL_FALSE;
 193    }
 194
 195    return GL_TRUE;
 196 }
 197
 198
 199 /**
 200  * Is 'mode' a valid value for glBegin(), glDrawArrays(), glDrawElements(),
 201  * etc?  The set of legal values depends on whether geometry shaders/programs
 202  * are supported.
 203  */
 204 GLboolean
 205 _mesa_valid_prim_mode(struct gl_context *ctx, GLenum mode, const char *name)
 206 {
 207    bool valid_enum;
 208
 209    switch (mode) {
 210    case GL_POINTS:
 211    case GL_LINES:
 212    case GL_LINE_LOOP:
 213    case GL_LINE_STRIP:
 214    case GL_TRIANGLES:
 215    case GL_TRIANGLE_STRIP:
 216    case GL_TRIANGLE_FAN:
 217       valid_enum = true;
 218       break;
 219    case GL_QUADS:
 220    case GL_QUAD_STRIP:
 221    case GL_POLYGON:
 222       valid_enum = (ctx->API == API_OPENGL_COMPAT);
 223       break;
 224    case GL_LINES_ADJACENCY:
 225    case GL_LINE_STRIP_ADJACENCY:
 226    case GL_TRIANGLES_ADJACENCY:
 227    case GL_TRIANGLE_STRIP_ADJACENCY:
 228       valid_enum = _mesa_is_desktop_gl(ctx)
 229          && ctx->Extensions.ARB_geometry_shader4;
 230       break;
 231    default:
 232       valid_enum = false;
 233       break;
 234    }
 235
 236    if (!valid_enum) {
 237       _mesa_error(ctx, GL_INVALID_ENUM, "%s(mode=%x)", name, mode);
 238       return GL_FALSE;
 239    }
 240
 241    /* From the GL_EXT_transform_feedback spec:
 242     *
 243     *     "The error INVALID_OPERATION is generated if Begin, or any command
 244     *      that performs an explicit Begin, is called when:
 245     *
 246     *      * a geometry shader is not active and <mode> does not match the
 247     *        allowed begin modes for the current transform feedback state as
 248     *        given by table X.1.
 249     *
 250     *      * a geometry shader is active and the output primitive type of the
 251     *        geometry shader does not match the allowed begin modes for the
 252     *        current transform feedback state as given by table X.1.
 253     *
 254     */
 255    if (ctx->TransformFeedback.CurrentObject->Active &&
 256        !ctx->TransformFeedback.CurrentObject->Paused) {
 257       GLboolean pass = GL_TRUE;
 258
 259       switch (mode) {
 260       case GL_POINTS:
 261          pass = ctx->TransformFeedback.Mode == GL_POINTS;
 262          break;
 263       case GL_LINES:
 264       case GL_LINE_STRIP:
 265       case GL_LINE_LOOP:
 266          pass = ctx->TransformFeedback.Mode == GL_LINES;
 267          break;
 268       default:
 269          pass = ctx->TransformFeedback.Mode == GL_TRIANGLES;
 270          break;
 271       }
 272       if (!pass) {
 273          _mesa_error(ctx, GL_INVALID_OPERATION,
 274                      "%s(mode=%s vs transform feedback %s)",
 275                      name,
 276                      _mesa_lookup_prim_by_nr(mode),
 277                      _mesa_lookup_prim_by_nr(ctx->TransformFeedback.Mode));
 278          return GL_FALSE;
 279       }
 280    }
 281
 282    return GL_TRUE;
 283 }
 284
 285 /**
 286  * Verify that the element type is valid.
 287  *
 288  * Generates \c GL_INVALID_ENUM and returns \c false if it is not.
 289  */
 290 static bool
 291 valid_elements_type(struct gl_context *ctx, GLenum type, const char *name)
 292 {
 293    switch (type) {
 294    case GL_UNSIGNED_BYTE:
 295    case GL_UNSIGNED_SHORT:
 296    case GL_UNSIGNED_INT:
 297       return true;
 298
 299    default:
 300       _mesa_error(ctx, GL_INVALID_ENUM, "%s(type = %s)", name,
 301                   _mesa_lookup_enum_by_nr(type));
 302       return false;
 303    }
 304 }
 305
 306 /**
 307  * Error checking for glDrawElements().  Includes parameter checking
 308  * and VBO bounds checking.
 309  * \return GL_TRUE if OK to render, GL_FALSE if error found
 310  */
 311 GLboolean
 312 _mesa_validate_DrawElements(struct gl_context *ctx,
 313                             GLenum mode, GLsizei count, GLenum type,
 314                             const GLvoid *indices, GLint basevertex)
 315 {
 316    ASSERT_OUTSIDE_BEGIN_END_WITH_RETVAL(ctx, GL_FALSE);
 317    FLUSH_CURRENT(ctx, 0);
 318
 319    if (count <= 0) {
 320       if (count < 0)
 321          _mesa_error(ctx, GL_INVALID_VALUE, "glDrawElements(count)" );
 322       return GL_FALSE;
 323    }
 324
 325    if (!_mesa_valid_prim_mode(ctx, mode, "glDrawElements")) {
 326       return GL_FALSE;
 327    }
 328
 329    if (!valid_elements_type(ctx, type, "glDrawElements"))
 330       return GL_FALSE;
 331
 332    if (!check_valid_to_render(ctx, "glDrawElements"))
 333       return GL_FALSE;
 334
 335    /* Vertex buffer object tests */
 336    if (_mesa_is_bufferobj(ctx->Array.ArrayObj->ElementArrayBufferObj)) {
 337       /* use indices in the buffer object */
 338       /* make sure count doesn't go outside buffer bounds */
 339       if (index_bytes(type, count) > ctx->Array.ArrayObj->ElementArrayBufferObj->Size) {
 340          _mesa_warning(ctx, "glDrawElements index out of buffer bounds");
 341          return GL_FALSE;
 342       }
 343    }
 344    else {
 345       /* not using a VBO */
 346       if (!indices)
 347          return GL_FALSE;
 348    }
 349
 350    if (!check_index_bounds(ctx, count, type, indices, basevertex))
 351       return GL_FALSE;
 352
 353    return GL_TRUE;
 354 }
 355
 356
 357 /**
 358  * Error checking for glMultiDrawElements().  Includes parameter checking
 359  * and VBO bounds checking.
 360  * \return GL_TRUE if OK to render, GL_FALSE if error found
 361  */
 362 GLboolean
 363 _mesa_validate_MultiDrawElements(struct gl_context *ctx,
 364                                  GLenum mode, const GLsizei *count,
 365                                  GLenum type, const GLvoid * const *indices,
 366                                  GLuint primcount, const GLint *basevertex)
 367 {
 368    unsigned i;
 369
 370    ASSERT_OUTSIDE_BEGIN_END_WITH_RETVAL(ctx, GL_FALSE);
 371    FLUSH_CURRENT(ctx, 0);
 372
 373    for (i = 0; i < primcount; i++) {
 374       if (count[i] <= 0) {
 375          if (count[i] < 0)
 376             _mesa_error(ctx, GL_INVALID_VALUE,
 377                         "glMultiDrawElements(count)" );
 378          return GL_FALSE;
 379       }
 380    }
 381
 382    if (!_mesa_valid_prim_mode(ctx, mode, "glMultiDrawElements")) {
 383       return GL_FALSE;
 384    }
 385
 386    if (!valid_elements_type(ctx, type, "glMultiDrawElements"))
 387       return GL_FALSE;
 388
 389    if (!check_valid_to_render(ctx, "glMultiDrawElements"))
 390       return GL_FALSE;
 391
 392    /* Vertex buffer object tests */
 393    if (_mesa_is_bufferobj(ctx->Array.ArrayObj->ElementArrayBufferObj)) {
 394       /* use indices in the buffer object */
 395       /* make sure count doesn't go outside buffer bounds */
 396       for (i = 0; i < primcount; i++) {
 397          if (index_bytes(type, count[i]) >
 398              ctx->Array.ArrayObj->ElementArrayBufferObj->Size) {
 399             _mesa_warning(ctx,
 400                           "glMultiDrawElements index out of buffer bounds");
 401             return GL_FALSE;
 402          }
 403       }
 404    }
 405    else {
 406       /* not using a VBO */
 407       for (i = 0; i < primcount; i++) {
 408          if (!indices[i])
 409             return GL_FALSE;
 410       }
 411    }
 412
 413    for (i = 0; i < primcount; i++) {
 414       if (!check_index_bounds(ctx, count[i], type, indices[i],
 415                               basevertex ? basevertex[i] : 0))
 416          return GL_FALSE;
 417    }
 418
 419    return GL_TRUE;
 420 }
 421
 422
 423 /**
 424  * Error checking for glDrawRangeElements().  Includes parameter checking
 425  * and VBO bounds checking.
 426  * \return GL_TRUE if OK to render, GL_FALSE if error found
 427  */
 428 GLboolean
 429 _mesa_validate_DrawRangeElements(struct gl_context *ctx, GLenum mode,
 430                                  GLuint start, GLuint end,
 431                                  GLsizei count, GLenum type,
 432                                  const GLvoid *indices, GLint basevertex)
 433 {
 434    ASSERT_OUTSIDE_BEGIN_END_WITH_RETVAL(ctx, GL_FALSE);
 435    FLUSH_CURRENT(ctx, 0);
 436
 437    if (count <= 0) {
 438       if (count < 0)
 439          _mesa_error(ctx, GL_INVALID_VALUE, "glDrawRangeElements(count)" );
 440       return GL_FALSE;
 441    }
 442
 443    if (!_mesa_valid_prim_mode(ctx, mode, "glDrawRangeElements")) {
 444       return GL_FALSE;
 445    }
 446
 447    if (end < start) {
 448       _mesa_error(ctx, GL_INVALID_VALUE, "glDrawRangeElements(end<start)");
 449       return GL_FALSE;
 450    }
 451
 452    if (!valid_elements_type(ctx, type, "glDrawRangeElements"))
 453       return GL_FALSE;
 454
 455    if (!check_valid_to_render(ctx, "glDrawRangeElements"))
 456       return GL_FALSE;
 457
 458    /* Vertex buffer object tests */
 459    if (_mesa_is_bufferobj(ctx->Array.ArrayObj->ElementArrayBufferObj)) {
 460       /* use indices in the buffer object */
 461       /* make sure count doesn't go outside buffer bounds */
 462       if (index_bytes(type, count) > ctx->Array.ArrayObj->ElementArrayBufferObj->Size) {
 463          _mesa_warning(ctx, "glDrawRangeElements index out of buffer bounds");
 464          return GL_FALSE;
 465       }
 466    }
 467    else {
 468       /* not using a VBO */
 469       if (!indices)
 470          return GL_FALSE;
 471    }
 472
 473    if (!check_index_bounds(ctx, count, type, indices, basevertex))
 474       return GL_FALSE;
 475
 476    return GL_TRUE;
 477 }
 478
 479
 480 /**
 481  * Called from the tnl module to error check the function parameters and
 482  * verify that we really can draw something.
 483  * \return GL_TRUE if OK to render, GL_FALSE if error found
 484  */
 485 GLboolean
 486 _mesa_validate_DrawArrays(struct gl_context *ctx,
 487                           GLenum mode, GLint start, GLsizei count)
 488 {
 489    ASSERT_OUTSIDE_BEGIN_END_WITH_RETVAL(ctx, GL_FALSE);
 490    FLUSH_CURRENT(ctx, 0);
 491
 492    if (count <= 0) {
 493       if (count < 0)
 494          _mesa_error(ctx, GL_INVALID_VALUE, "glDrawArrays(count)" );
 495       return GL_FALSE;
 496    }
 497
 498    if (!_mesa_valid_prim_mode(ctx, mode, "glDrawArrays")) {
 499       return GL_FALSE;
 500    }
 501
 502    if (!check_valid_to_render(ctx, "glDrawArrays"))
 503       return GL_FALSE;
 504
 505    if (ctx->Const.CheckArrayBounds) {
 506       if (start + count > (GLint) ctx->Array.ArrayObj->_MaxElement)
 507          return GL_FALSE;
 508    }
 509
 510    return GL_TRUE;
 511 }
 512
 513
 514 GLboolean
 515 _mesa_validate_DrawArraysInstanced(struct gl_context *ctx, GLenum mode, GLint first,
 516                                    GLsizei count, GLsizei numInstances)
 517 {
 518    ASSERT_OUTSIDE_BEGIN_END_WITH_RETVAL(ctx, GL_FALSE);
 519    FLUSH_CURRENT(ctx, 0);
 520
 521    if (count <= 0) {
 522       if (count < 0)
 523          _mesa_error(ctx, GL_INVALID_VALUE,
 524                      "glDrawArraysInstanced(count=%d)", count);
 525       return GL_FALSE;
 526    }
 527
 528    if (first < 0) {
 529       _mesa_error(ctx, GL_INVALID_VALUE,
 530                   "glDrawArraysInstanced(start=%d)", first);
 531       return GL_FALSE;
 532    }
 533
 534    if (!_mesa_valid_prim_mode(ctx, mode, "glDrawArraysInstanced")) {
 535       return GL_FALSE;
 536    }
 537
 538    if (numInstances <= 0) {
 539       if (numInstances < 0)
 540          _mesa_error(ctx, GL_INVALID_VALUE,
 541                      "glDrawArraysInstanced(numInstances=%d)", numInstances);
 542       return GL_FALSE;
 543    }
 544
 545    if (!check_valid_to_render(ctx, "glDrawArraysInstanced(invalid to render)"))
 546       return GL_FALSE;
 547
 548    if (ctx->Const.CheckArrayBounds) {
 549       if (first + count > (GLint) ctx->Array.ArrayObj->_MaxElement)
 550          return GL_FALSE;
 551    }
 552
 553    return GL_TRUE;
 554 }
 555
 556
 557 GLboolean
 558 _mesa_validate_DrawElementsInstanced(struct gl_context *ctx,
 559                                      GLenum mode, GLsizei count, GLenum type,
 560                                      const GLvoid *indices, GLsizei numInstances,
 561                                      GLint basevertex)
 562 {
 563    ASSERT_OUTSIDE_BEGIN_END_WITH_RETVAL(ctx, GL_FALSE);
 564    FLUSH_CURRENT(ctx, 0);
 565
 566    if (count <= 0) {
 567       if (count < 0)
 568          _mesa_error(ctx, GL_INVALID_VALUE,
 569                      "glDrawElementsInstanced(count=%d)", count);
 570       return GL_FALSE;
 571    }
 572
 573    if (!_mesa_valid_prim_mode(ctx, mode, "glDrawElementsInstanced")) {
 574       return GL_FALSE;
 575    }
 576
 577    if (!valid_elements_type(ctx, type, "glDrawElementsInstanced"))
 578       return GL_FALSE;
 579
 580    if (numInstances <= 0) {
 581       if (numInstances < 0)
 582          _mesa_error(ctx, GL_INVALID_VALUE,
 583                      "glDrawElementsInstanced(numInstances=%d)", numInstances);
 584       return GL_FALSE;
 585    }
 586
 587    if (!check_valid_to_render(ctx, "glDrawElementsInstanced"))
 588       return GL_FALSE;
 589
 590    /* Vertex buffer object tests */
 591    if (_mesa_is_bufferobj(ctx->Array.ArrayObj->ElementArrayBufferObj)) {
 592       /* use indices in the buffer object */
 593       /* make sure count doesn't go outside buffer bounds */
 594       if (index_bytes(type, count) > ctx->Array.ArrayObj->ElementArrayBufferObj->Size) {
 595          _mesa_warning(ctx,
 596                        "glDrawElementsInstanced index out of buffer bounds");
 597          return GL_FALSE;
 598       }
 599    }
 600    else {
 601       /* not using a VBO */
 602       if (!indices)
 603          return GL_FALSE;
 604    }
 605
 606    if (!check_index_bounds(ctx, count, type, indices, basevertex))
 607       return GL_FALSE;
 608
 609    return GL_TRUE;
 610 }
 611
 612
 613 GLboolean
 614 _mesa_validate_DrawTransformFeedback(struct gl_context *ctx,
 615                                      GLenum mode,
 616                                      struct gl_transform_feedback_object *obj,
 617                                      GLuint stream,
 618                                      GLsizei numInstances)
 619 {
 620    ASSERT_OUTSIDE_BEGIN_END_WITH_RETVAL(ctx, GL_FALSE);
 621    FLUSH_CURRENT(ctx, 0);
 622
 623    if (!_mesa_valid_prim_mode(ctx, mode, "glDrawTransformFeedback*(mode)")) {
 624       return GL_FALSE;
 625    }
 626
 627    if (!obj) {
 628       _mesa_error(ctx, GL_INVALID_VALUE, "glDrawTransformFeedback*(name)");
 629       return GL_FALSE;
 630    }
 631
 632    if (!obj->EndedAnytime) {
 633       _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawTransformFeedback*");
 634       return GL_FALSE;
 635    }
 636
 637    if (stream >= ctx->Const.MaxVertexStreams) {
 638       _mesa_error(ctx, GL_INVALID_VALUE,
 639                   "glDrawTransformFeedbackStream*(index>=MaxVertexStream)");
 640       return GL_FALSE;
 641    }
 642
 643    if (numInstances <= 0) {
 644       if (numInstances < 0)
 645          _mesa_error(ctx, GL_INVALID_VALUE,
 646                      "glDrawTransformFeedback*Instanced(numInstances=%d)",
 647                      numInstances);
 648       return GL_FALSE;
 649    }
 650
 651    if (!check_valid_to_render(ctx, "glDrawTransformFeedback*")) {
 652       return GL_FALSE;
 653    }
 654
 655    return GL_TRUE;
 656 }