Graphics Reference
In-Depth Information
in the screen resolution, multiple screens being used by OpenGL ES context,
or an out-of-memory event that causes the mapped memory to be discarded.
1
The code in Example 6-8 demonstrates the use of
glMapBufferRange
and
glUnmapBuffer
to write the contents of vertex buffer objects.
Example 6-8
Mapping a Buffer Object for Writing
GLfloat *vtxMappedBuf;
GLushort *idxMappedBuf;
glGenBuffers ( 2, userData->vboIds );
glBindBuffer ( GL_ARRAY_BUFFER, userData->vboIds[0] );
glBufferData ( GL_ARRAY_BUFFER, vtxStride * numVertices,
NULL, GL_STATIC_DRAW );
vtxMappedBuf = (GLfloat*)
glMapBufferRange ( GL_ARRAY_BUFFER, 0,
vtxStride * numVertices,
GL_MAP_WRITE_BIT |
GL_MAP_INVALIDATE_BUFFER_BIT );
if ( vtxMappedBuf == NULL )
{
esLogMessage( "Error mapping vertex buffer object." );
return;
}
// Copy the data into the mapped buffer
memcpy ( vtxMappedBuf, vtxBuf, vtxStride * numVertices );
// Unmap the buffer
if ( glUnmapBuffer( GL_ARRAY_BUFFER ) == GL_FALSE )
{
esLogMessage( "Error unmapping array buffer object." );
return;
}
// Map the index buffer
glBindBuffer ( GL_ELEMENT_ARRAY_BUFFER,
userData->vboIds[1] );
glBufferData ( GL_ELEMENT_ARRAY_BUFFER,
sizeof(GLushort) * numIndices,
NULL, GL_STATIC_DRAW );
(continues)
1.
If the screen resolution changes to a larger width, height, and bits per pixel at
runtime, the mapped memory may have to be released. Note that this is not a
very common issue on handheld devices. A backing store is rarely implemented
on most handheld and embedded devices. Therefore, an out-of-memory event will
result in memory being freed and becoming available for reuse for critical needs.
