Vertex Attributes, Vertex Arrays, and Buffer Objects - Praise for OpenGL ES 30 Programming Guide - page 158

Example 6-8 Mapping a Buffer Object for Writing (continued)

idxMappedBuf = (GLushort*)
glMapBufferRange ( GL_ELEMENT_ARRAY_BUFFER, 0,
sizeof(GLushort) * numIndices,
GL_MAP_WRITE_BIT |
GL_MAP_INVALIDATE_BUFFER_BIT );
if ( idxMappedBuf == NULL )
{
esLogMessage( "Error mapping element buffer object." );
return;
}

// Copy the data into the mapped buffer
memcpy ( idxMappedBuf, indices,
sizeof(GLushort) * numIndices );

// Unmap the buffer
if ( glUnmapBuffer( GL_ELEMENT_ARRAY_BUFFER ) == GL_FALSE )
{
esLogMessage( "Error unmapping element buffer object." );
return;
}

Flushing a Mapped Buffer

An application may wish to map a range (or all) of a buffer object using
glMapBufferRange , but update only discrete subregions of the mapped
range. To avoid the potential performance penalty for flushing the entire
mapped range when calling glUnmapBuffer , the application can map
with the GL_MAP_FLUSH_EXPLICIT_BIT access flag (along with GL_MAP_
WRITE_BIT ). When the application has finished updating a portion of the
mapped range, it can indicate this fact using glFlushMappedBufferRange .

void * glFlushMappedBufferRange (GLenum target ,
GLintptr offset,
GLsizeiptr length )

target can be set to any of the following targets:

GL_ARRAY_BUFFER
GL_ELEMENT_ARRAY_BUFFER
GL_COPY_READ_BUFFER
GL_COPY_WRITE_BUFFER
GL_PIXEL_PACK_BUFFER
GL_PIXEL_UNPACK_BUFFER