CODEWITHSUNDEEP
opengl
AlexXsWx
AlexXsWx

Reputation: 123

glMultiDrawElements

I read the red book (7th edition) and while testing glMultiDrawElements I got nothing on my screen, and "Access violation" error in debug console. I use MVS2010, and here are main code parts I compile:

// C4UB_V2F interwined format, vertex are CCW ordered
static const GLfloat vertex[] = {

    // First triangle
    0xff0000ff, 0.25f, 1.0f, // nevermind on that incorrect integer colors
    0x00ff00ff, 0.0f,  0.0f,
    0x0000ffff, 0.5f,  0.0f,

    // Second one
    0xff0000ff, 0.75f, 0.0f,
    0x00ff00ff, 0.5f,  1.0f,
    0x0000ffff, 1.0f,  1.0f

};


void init() {

    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glShadeModel(GL_SMOOTH);
    glInterleavedArrays(GL_C4UB_V2F, 0, vertex);

}


static const GLubyte order[] = { 0, 1, 2, 3, 4, 5 };

static GLubyte oneIndices[] = {0, 1, 2};
static GLubyte twoIndices[] = {3, 4, 5};
static GLsizei count[] = {3, 3};
static GLvoid * indices[2] = {oneIndices, twoIndices};

void render() {

    glClear(GL_COLOR_BUFFER_BIT);

    // This one works perfectly:
    //glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, order); 

    // And this one generates access violation error
    // in the book there's no indices casting, but MVS2010 is too lazy to cast it itself
    glMultiDrawElements(GL_TRIANGLES, count, GL_UNSIGNED_BYTE, (const GLvoid **)indices, 2);


    // This command never executes 'cause of acces violation error occuring 
    glFlush();

}

Seems to me I've missed something while casting indices, but I can't get what exactly. Any ideas?

Upvotes: 1

Views: 2682

Answers (2)

Nicol Bolas
Nicol Bolas

Reputation: 474376

I just checked - printf("%i", glDrawElementsInstanced); is printing zero.

There are two possibilities for that.

  1. Your OpenGL implementation doesn't support them. This would mean that you have ancient drivers, or you aren't creating a context properly. Since you're using FreeGLUT, a context creation problem is unlikely. If your hardware was made in the last 7 years, you should be able to get them.

  2. You did not initialize GLEW. You must call glewInit after creating the OpenGL window with FreeGLUT. Otherwise, you will not have properly initialized GLEW, and your function pointers will be NULL.

Upvotes: 1

Christian Rau
Christian Rau

Reputation: 45968

Due to your comments it seems these functions are not supported by your hardware and/or driver. glMultiDrawElements is supported from 1.4 on and glDrawRangeElements is supported from 1.2 on. Make sure your hardware supports these versions and you got the latest drivers.

And of course you first have to retrieve the corresponding function pointers before you can use them. This can be done manually by means of wglGetProcAddress (assuming Windows due to your mentioning of VS) or by an extension loading library, like GLEW.

Upvotes: 0

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