Transparent overlay which does not scroll with its parent

I would like to have a form which has a few controls as transparent overlays over 开发者_如何学Ca bitmap. This bitmap is subject to transform matrix (zoom & scroll). I'm trying to achieve a look similar to GoogleMaps where the controls do not move when the background image is panned/zoomed.

I've tried to mimic this in my OnPaint. However, when the window is scrolled only the newly exposed area gets invalidated so my control doesn’t repaint.

I've tried to calculate where the old control was, invalidate that area, and also invalidate the area where it's supposed to have been. When I do this it flickers and you can still see the image as its scrolled.

I tried to put a ButtonControl on my display window. However, it always scrolls with its parent control. I tried to capture the scroll events and then adjust the position of the ButtonControl. This also has a delay update effect so it looks not so good.

Any ideas would be greatly appreciated.

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It sounds to me like you need to Invalidate() your control wich handles the OnPaint event.

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Unfortunately, you get the flicker because the Auto-scrolling mechanism sets its position, and then you restore it. The result is two messages being sent to the button.

Place your bitmap and scroll logic in a separate control that fill the entire form. That means both your bitmap control and the button are child controls of the form.

Alternatively, draw the button yourself. You will then of course need to do some work on getting it to respond to mouse clicks etc. The ControlPaint class has methods that help you mimic the appearance of Windows controls.