Device Types and Index Processing Requirements
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4/8/2010
The performance of index processing operations depends heavily on where the index buffer exists in memory and what type of rendering device is being used. Applications control the memory allocation for index buffers when they are created. When the D3DMPOOL_SYSTEMMEM memory flag (see D3DMPOOL) is set, the index buffer is created in system memory. When the D3DMPOOL_VIDEOMEM memory flag is used, the device driver allocated the index buffer in video memory.
The application can directly write indices to a index buffer allocated in driver-optimal memory. This technique prevents a redundant copy operation later. This technique does not work well if your application reads data back from an index buffer, because read operations done by the host from driver-optimal memory can be very slow. Therefore, if your application needs to read during processing or writes data to the buffer erratically, a system-memory index buffer is a better choice.