Question

I have a Control that can overlay multiple C# user controls in my GUI. This control has a semi-transparent background in order to ‘grey-out’ portions of the GUI and the class looks somethink like this:

public greyOutControl: UserControl
{
    // Usual stuff here

    protected overide OnPaint()
    {
        paintBackround();

        base.OnPaint();
    }
}

Currently the control sometimes gets caught in a loop and constantly re-draws the background, making the semi-transparent color appear less and less transparent.

My idea to combat this is the following (in broad terms):

1) Determine what controls the greyOutControl is on top of
2) call Refresh() on those controls to update the display
3) continue drawing the greyOutControl.

My question is: How can I determine which controls the greyOutControl overlaps?, or is there a way that I can refresh only the part of the GUI that greyOutControl covers?

Answer 1

The solution to this problem I found was to programmatically take a screen shot of the area being overlayed and then use that image as the background for the control being overlayed. This then allows you to put the alpha overlay into the image within the OnPaint() method and the control to draw itself correctly.

This does have the disadvantage that the background isn’t updated in the overlapping control, but unless there was a number of event handlers watching if something changes and then update the overlayed control I cant see any way around the issue. Sometimes I regret not trying to use WPF!