Updating the screen without flicker

SUMMARY

This article describes a technique for drawing to a window Device Context (DC) in such a way that the screen does not flicker. The technique is very simple and easy to implement.

Many applications written for the Microsoft Windows operating system maintain status information such as the current time in a small control window that flickers very annoyingly each time it's updated. All standard Windows controls flicker if updated at frequent intervals. The solution to this problem is to implement a simple control and use an off-screen device context (DC) to construct the image, which is then copied in total to the client area of the control window. The net result is a control that can be updated without causing any flicker.

FLICKER has window procedures for two controls--one of these flickers; the other one doesn't. The application creates an instance of each of these controls and updates the window text ten times every second to show how one flickers and the other doesn't. Both controls support the system text color, window background color, and the WM_SETTEXT and WM_SETFONT messages.