Question

I am trying to make simple app that allows one to compare image to transparent PNG templates, by dragging the template over picture. For this I need a way to create a PictureBox that will contain the PNG image and be transparent where the the png is transparent. Everything works fine but the transparency part: When I load a PNG image to the PictureBox (background color is set to transparent) it shows the background color of the containing panel rather than the image that it hovers.

I searched but only found a way to make the PictureBox completely transparent.

Answer 1

It is difficult to make a control that is partially transparent.

What you should do is handle the lower PictureBox s Paint event (the one that does not need to be transparent), and draw the overlay image using e.Graphics.DrawImage(image, x, y). This will draw transparent and semi-transparent images correctly.

EDIT: In response to your comment, there s nothing wrong with calling the Invalidate method in the MouseMove event. However, you will notice some flickering. To solve the flickering, make a control that inherits PictureBox, and call SetStyle(ControlStyles.DoubleBuffered, true) in the constructor.

Answer 2

This works fine if you add the pictureBoxOnTop to the list of controls of the pictureBoxToBeHovered to be hovered.

        pictureBoxToBeHovered.Controls.Add(pictureBoxOnTop);
        pictureBoxOnTop.BackColor = Color.Transparent;
        pictureBoxOnTop .Location = new Point(0,0) ;

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