Never does DrvSaveScreenBits been called

Dear All,
I implemented a mirror display driver, in fact, it works well. I wanted to improve the performance of mirror, especially displayed a menu or dialog box, so I used DrvSaveScreenBits to approach it, but I found DrvSaveScreenBits is never called by GDI, why? (yes, DrvSaveScreenBits doesn’t work, mirror works normally yet, I only want to know why it doesn’t work.)
The surface type is device-managed surface, and I had added {INDEX_DrvSaveScreenBits, (PFN)DrvSaveScreenBits} to DRVFN structure. Should I add others?

Best regards,

Did you sloved it?

> Did you sloved it?

NO, GDI didn’t call DrvSaveScreenBits, but DrvCopyBits when displaying context menu or dialog, I dont’ know why.