Hi,
You can use the EDSP_ definitions to check for all the different pixelformats. See a list of them here:
http://www.edgelib.com/index.php?node=1 ... dsp_true16
When locking the backbuffer you can expect EDSP_INDEXED8 (only for pc builds when specified specifically), EDSP_TRUE12, EDSP_TRUE16 or EDSP_TRUE32. Other colordepths are emulated.