EXC_BAD_ACCESS on glDrawElements and Vertex Buffer Objects

SDL Development
7

Hi Leonard,

I’ve taken a look at GL_ARB_vertex_buffer_object, but that did not reveal any
errors in your code to me. However, you did not show the part where you are
calling glBufferData to fill the buffers.

Anyway, I have two theories:

#1
GLUT and SDL might use a different setup of the screen or window, causing
different GL implementations to be used. For example, I’ve learned that on my
Windows system, requesting 32 bits of depth buffer causes a fallback to MS’
software GL. NVidia’s hardware GL will only work up to 24 bits of depth (at
least for my video card and driver).
I do not know whether something similar is possible on OSX.

If different GLs are at work, the one enabled by GLUT might not support VBOs.
The program would then just run the “else” code, which we know doesn’t fail.

So, unless you already did, try and verify that the VBO code is actually called
when using GLUT.

#2
If VBO support is present in both cases, try checking glError after every GL
function call.

For example, if glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, …) failed, no buffer
object would be bound. Then glDrawElements would have to use BUFFER_OFFSET(0),
which evaluates to a NULL pointer, as a regular pointer to the index data in
system memory. It would thus dereference a NULL pointer.
And although I don’t know much about OSX, EXC_BAD_ACCESS sure sounds like it is
the expected result of dereferencing a NULL pointer.

MartinOn 03.11.2010 17:07, Leonard Teo wrote:

Hi guys,

I wrote a simple application using GLUT that I’m porting to SDL now to turn it into a game.

I am having a bizarre issue specifically with using glDrawElements and Vertex Buffer Objects, SDL 1.2.14 OSX. If I don’t use VBO’s the program runs fine. It only throws a “EXC_BAD_ACCESS” when using VBO’s. To make the matter more obscure. The program runs totally fine in GLUT. Am I missing something?

Any help would be most appreciated.

Thanks,

Leonard

Here’s the drawing code:

if (glewGetExtension(“GL_ARB_vertex_buffer_object”))
{
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);

  //Load vertices
  glBindBuffer(GL_ARRAY_BUFFER, this->mesh->vbo_vertices);
  glVertexPointer(3, GL_FLOAT, 0, BUFFER_OFFSET(0));
  
  //Load normals
  glBindBuffer(GL_ARRAY_BUFFER, this->mesh->vbo_normals);
  glNormalPointer(GL_FLOAT, 0, BUFFER_OFFSET(0));

  //Load UVs
  glBindBuffer(GL_ARRAY_BUFFER, this->mesh->vbo_uvs);
  glTexCoordPointer(2, GL_FLOAT, 0, BUFFER_OFFSET(0));

  glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this->mesh->vbo_index);
  App dies here ----->  glDrawElements(GL_TRIANGLES, 3*this->mesh->numFaces, GL_UNSIGNED_INT, BUFFER_OFFSET(0));

  glDisableClientState(GL_VERTEX_ARRAY);
  glDisableClientState(GL_NORMAL_ARRAY);
  glDisableClientState(GL_TEXTURE_COORD_ARRAY);

} else {

  //BTW: If I run this block of code instead of the above, everything renders fine. App doesn't die.

  //Drawing with vertex arrays
  glEnableClientState(GL_VERTEX_ARRAY);
  glEnableClientState(GL_NORMAL_ARRAY);
  glEnableClientState(GL_TEXTURE_COORD_ARRAY);

  glVertexPointer(3, GL_FLOAT, 0, this->mesh->vertexArray);
  glNormalPointer(GL_FLOAT, 0, this->mesh->normalsArray);
  glTexCoordPointer(2, GL_FLOAT, 0, this->mesh->uvArray);

  glDrawElements(GL_TRIANGLES, 3*this->mesh->numFaces, GL_UNSIGNED_INT, this->mesh->indexArray);

  glDisableClientState(GL_VERTEX_ARRAY);
  glDisableClientState(GL_NORMAL_ARRAY);
  glDisableClientState(GL_TEXTURE_COORD_ARRAY);

}

Here’s the debug information:

Program received signal: ?EXC_BAD_ACCESS?.

Thread-1-<com.apple.main-thread>
#0 0x17747a93 in gleRunVertexSubmitImmediate
#1 0x1774772c in gleLLVMArrayFunc
#2 0x177476e4 in gleSetVertexArrayFunc
#3 0x1773073c in gleDrawArraysOrElements_ExecCore
#4 0x176baa7b in glDrawElements_Exec
#5 0x97524050 in glDrawElements

asm gleRunVertexSubmitImmediate

0x17747a93<+0771> mov (%eax,%ecx,4),%eax ← the app dies on this.

Here’s my SDL initialization code:

//Initialize SDL
if (SDL_Init(SDL_INIT_VIDEO)< 0)
{
cout<< “Could not initialize SDL”<< endl<< SDL_GetError();
exit(2);
}

//Set window
SDL_WM_SetCaption(“Hello World!”, “Hello World!”);

//Set openGL window
if ( SDL_SetVideoMode(width, height, 32, SDL_OPENGL | SDL_RESIZABLE) == NULL ) {
cout<< “Unable to create OpenGL context: %s\n”<< endl<< SDL_GetError();
SDL_Quit();
exit(2);
}

//Set up event handling
SDL_Event event;
bool quit = false;

//Initialize GLEW
GLenum err = glewInit();
if (GLEW_OK != err)
{
//Problem: glewInit failed, something is seriously wrong.
fprintf(stderr, “Error: %s\n”, glewGetErrorString(err));
exit(1);
}
fprintf(stdout, “Status: Using GLEW %s\n”, glewGetString(GLEW_VERSION));

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