Matthew Webster wrote:
I need to draw a somethings over a background image
periodically. For example, draw minute hand and
second hand on a clock image. To do so, I have to
erase current hands first then draw new hands. But
erasing hands will destroy the clock image. So I have
redraw clock image and before drawing new hands. Is
there any way to avoid redrawing background image?
You could XOR in the hands, or store the clobbered section somewhere else.
The best solution, however, is to treat the symptom, not the cause. The
problem with erasing and redrawing is that it causes a noticeable flicker.
You can eliminate that flicker with double-buffering: draw both the
background and the hands to an off-screen buffer, then copy that onto the
main screen.
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