c++ - Correct method for redrawing a layered window -

i have window created ws_ex_layered window style. drawing onto memory bitmap using gdi+, , using updatelayeredwindow update graphical content of layered window. intend use window main window of application, require redraw frequently.

seeing layered windows not receive wm_paint windows message^[?], need come appropriate method re-drawing window. optimisation not essential, it's nice have cake , eat too. therefore, in search of "correct" method use.

here thoughts far:

• i guess it's idea render onto off-screen bitmap before bitblting or similar.

• 60 frames rendered per second should (more than?) enough (but how compare other applications' frame rates?).

possible solutions:

• use settimer send wm_timer message on regular basis.

  • useful because through specifying time-out value, can achieve desired frames per second, without requirement measure duration "frame" takes rendered.

  • would cause input or other lags due frequency , speed of messages.

• render frames when particular events occur, such window resize.

  • would require me figure out events require redraw.

  • would reduce amount of unnecessary frames being rendered.

• render frames when there no messages in message queue, checking peekmessage.

  • this might slow down processing of window messages.

  • this cause high cpu usage because more frames necessary being processed.

• create new thread perform render loop.

  • timing calculations have performed in order maintain steady frame-rate.

layered windows don't receive wm_paint messages otherwise generated after window visibility changed, won't prevent them receive message @ all.

you can continue use invalidaterect change window update region, wait wm_paint in window procedure, draw contents in bitmap , call updatelayeredwindow change window contents. can use method request redraw when content of window changes, example, when button pressed, or window has been resized (or activated/deactivated).