c# Winforms: Refreshing a portion of a GUI (containing 1 or more controls)

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

I don't see a direct way of finding the overlapping controls. I think you might need to check the whole control tree to find out that. About refreshing, you can use Control.Invalidate(Rectangle) method to specify which part to refresh.

Answer 2

Why don't you keep track of your transparent controls and paint them after all the other controls are drawn?. Painting anything at the top of the Z-order shouldn't cause the other controls to be repainted.