.NET (Core and Framework)

if (this.RenderTransparent)
    this.PaintTransparentBackground(e, rectangle);

internal void PaintTransparentBackground(PaintEventArgs e, Rectangle rectangle) 
{
    Graphics local0;
    Control local1;
    POINT local2;
    PaintEventArgs local3;
    GraphicsState local4;
    int local5;

    local0 = e.Graphics;
    local1 = this.ParentInternal;
    if (local1 != null) 
    {
        // If we have a parent, copy its client area
        local2 = new POINT();
        local2.y = (local5 = 0);
        local2.x = local5;
        UnsafeNativeMethods.MapWindowPoints(new HandleRef(this, this.Handle), new HandleRef(local1, local1.Handle), local2, 1);
        rectangle.Offset(local2.x, local2.y);
        local3 = new PaintEventArgs(local0, rectangle);
        local4 = local0.Save();

        try 
        {
            local0.TranslateTransform((float) -local2.x, (float) -local2.y);
            this.InvokePaintBackground(local1, local3);
            local0.Restore(local4);
            local4 = local0.Save();
            local0.TranslateTransform((float) -local2.x, (float) -local2.y);
            this.InvokePaint(local1, local3);
        }
        finally
        {
            local0.Restore(local4);
        }
    }

    // Here it is:
    // What was Microsoft thinking???!!!
    // After all that work, this just paints over it all!
    local0.FillRectangle(SystemBrushes.Control, rectangle);
}