The following illustration shows the format of execute buffers. Note that all data in an execute buffer must be DWORD-aligned.
The instruction stream consists of operation codes, or opcodes, and the data that is operated on by those opcodes. The opcodes define how the vertex list should be lit and rendered. Direct3D opcodes are listed in the D3DOPCODE enumerated type. The D3DINSTRUCTION structure describes instructions in an execute buffer; it contains an opcode, the size of each instruction data unit, and a count of the relevant data units that follow.
One of the most common instructions is a triangle list (D3DOP_TRIANGLE), which is simply a list of triangle primitives that reference vertices in the vertex list. Because all the primitives in the instruction stream reference vertices in the vertex list only, it is easy for the transformation module to reject a whole buffer of primitives if its vertices are outside the viewing frustum.