NeHe OpenGL Lesson45 - Vertex Buffer Objects

This samples shows us how to put the mesh render data such as the vertex position, texture coordinates and even more vertex data upload into the video hardware. The samples what saw before that vertex data provided by the glVertex3f or glTexCoord2f commands, or vertex array. All those stuff are located in the main memory. They will be submitted to GPU as needed. But most of those vertex data that will not be modified and static could be allocated in the video memory at startup. This will save the data transferring time and vertex format GPU optimized. Both of them will improve the render performance.

 

OpenGL Vertex Buffer Object extension Access

On windows, we need to use the OpenGL ARB extension to access those vertex buffer object functions. The following are the code that used to access OpenGL extensions:

g_fVBOSupported = IsExtensionSupported( "GL_ARB_vertex_buffer_object" );
if( g_fVBOSupported )
{
    // Get Pointers To The GL Functions
    glGenBuffersARB = (PFNGLGENBUFFERSARBPROC) wglGetProcAddress("glGenBuffersARB");
    glBindBufferARB = (PFNGLBINDBUFFERARBPROC) wglGetProcAddress("glBindBufferARB");
    glBufferDataARB = (PFNGLBUFFERDATAARBPROC) wglGetProcAddress("glBufferDataARB");
    glDeleteBuffersARB = (PFNGLDELETEBUFFERSARBPROC) wglGetProcAddress("glDeleteBuffersARB");
//...

 

Create Vertex buffer Objects

After the vertex data ready, then create the vertex buffer object, upload vertex data into the vertex buffer objects. The code as following:

// Generate And Bind The Vertex Buffer
glGenBuffersARB( 1, &m_nVBOVertices );                            // Get A Valid Name
glBindBufferARB( GL_ARRAY_BUFFER_ARB, m_nVBOVertices );            // Bind The Buffer
// Load The Data
glBufferDataARB( GL_ARRAY_BUFFER_ARB, m_nVertexCount*3*sizeof(float), 
    m_pVertices, GL_STATIC_DRAW_ARB );

// Generate And Bind The Texture Coordinate Buffer
glGenBuffersARB( 1, &m_nVBOTexCoords );                            // Get A Valid Name
glBindBufferARB( GL_ARRAY_BUFFER_ARB, m_nVBOTexCoords );        // Bind The Buffer
// Load The Data
glBufferDataARB( GL_ARRAY_BUFFER_ARB, m_nVertexCount*2*sizeof(float),
    m_pTexCoords, GL_STATIC_DRAW_ARB );

 

Render With Vertex Buffer Objects

// Enable Pointers
glEnableClientState( GL_VERTEX_ARRAY );        
glEnableClientState( GL_TEXTURE_COORD_ARRAY );

glBindBufferARB( GL_ARRAY_BUFFER_ARB, g_pMesh->m_nVBOVertices );
// Set The Vertex Pointer To The Vertex Buffer
glVertexPointer( 3, GL_FLOAT, 0, (char *) NULL );        

glBindBufferARB( GL_ARRAY_BUFFER_ARB, g_pMesh->m_nVBOTexCoords );
// Set The TexCoord Pointer To The TexCoord Buffer
glTexCoordPointer( 2, GL_FLOAT, 0, (char *) NULL );        

// Draw All Of The Triangles At Once
glDrawArrays( GL_TRIANGLES, 0, g_pMesh->m_nVertexCount );    

// Disable Pointers
glDisableClientState( GL_VERTEX_ARRAY );        
glDisableClientState( GL_TEXTURE_COORD_ARRAY );

 

Render With Vertex Array

The process render with vertex buffer objects is the same as render with vertex array. The code as following:

// Enable Pointers
glEnableClientState( GL_VERTEX_ARRAY );        
glEnableClientState( GL_TEXTURE_COORD_ARRAY );

glVertexPointer( 3, GL_FLOAT, 0, g_pMesh->m_pVertices ); 
glTexCoordPointer( 2, GL_FLOAT, 0, g_pMesh->m_pTexCoords );     

// Draw All Of The Triangles At Once
glDrawArrays( GL_TRIANGLES, 0, g_pMesh->m_nVertexCount );    

// Disable Pointers
glDisableClientState( GL_VERTEX_ARRAY );        
glDisableClientState( GL_TEXTURE_COORD_ARRAY );

 

Release Vertex Buffer Objects

unsigned int nBuffers[2] = { m_nVBOVertices, m_nVBOTexCoords };
glDeleteBuffersARB( 2, nBuffers );

 

The source code could be found here.