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GL_ARB_vertex_buffer_object

Started by akn81 Apr 20, 2003 at 4:09 AM 5 replies 1.1k views

Original Post

Apr 20, 2003 at 4:09 AM

Hi there, is anyone familiar with how to use this extension? I''ve heard that it has replaced VAR, but I don''t understand how to use it. I''m working on a 3d space sim, and was thinking for situations where many identical ships are onscreen perhaps it might be better to upload a single mesh to the video card, then call glTranslatef() for each ship before rendering the mesh. Is that a good idea?

The_Fallen

Apr 20, 2003 at 4:59 AM

Generate a buffer:

  
glGenBuffersARB(1, &m_BufferObject);

Bind the buffer and initilialize it with your geometry data:

  
glBindBufferARB(GL_ARRAY_BUFFER_ARB, m_BufferObject);
glBufferDataARB(GL_ARRAY_BUFFER_ARB, memorysize, m_Memory, GL_STATIC_DRAW_ARB);

Or GL_DYNAMIC_DRAW_ARB for a dynamic array.

And for drawing bind your buffer again:

  
glBindBufferARB(GL_ARRAY_BUFFER_ARB, m_BufferObject);

Tell OpenGL what data you''ve got:

  
glVertexPointer(3, GL_FLOAT, m_StructureSize, BUFFER_OFFSET(0));
glEnableClientState(GL_VERTEX_ARRAY);

BUFFER_OFFSET is something like this:

  
#define BUFFER_OFFSET(i)	((char *)NULL + (i))

And then draw like this:

  
glDrawElements(mode, count, GL_UNSIGNED_SHORT, indices);

The_Fallen

Apr 20, 2003 at 5:01 AM

And search on developer.nvidia.com, there are some really good papers about that topic.

akn81

Author

akn81

Apr 20, 2003 at 5:29 AM

Thanks for giving me the steps, but what is m_BufferObject and m_Memory? I''m sorry I couldn''t find any examples using vertex_buffer_object on Nvidia''s page, at best I got the specification from oss.sgi.com, but I just want a practical example, lets say to draw a cube. Can you help me out with that please?

_DarkWIng_

Apr 20, 2003 at 6:14 AM

at the end of extension documentation there are a bunch of examples how to use ARB_VBO with different settings (static/dynamic,....)

You should never let your fears become the boundaries of your dreams.

The_Fallen

Apr 21, 2003 at 10:11 AM

Sorry, here are my variables:

    
GLuint m_BufferObject;     // holds the buffer

int memorysize;            // total size of vertex memory

char *m_Memory;            // pointer to the vertex memory

                           // (need only a pointer, char not necessary)

int m_StructureSize;       // size in bytes of one vertex in memory

  

And in the call to glDrawElements():

      
mode    = GL_TRIANGLES, GL_TRIANGLE_STRIPS or whatsoever
count   = number of vertices
indices = pointer to the index array

[edited by - The_Fallen on April 21, 2003 2:54:33 PM]

akn81

Author

akn81

Apr 22, 2003 at 1:00 PM

Thank you! I''ll go and test it out now, if I run into problems I''ll let you know

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