WPF, C#: Draw a line onto existing bitmap in image control

Question

I have a bitmap image in an image control

I need to draw a red line on the bitmap each time I click with the mouse on

Answer 1

When you do Graphics.FromImage, this Graphics class (and also the System.Drawing.Pen) do not belong to WPF, they are part from WinForms and they are internally using Windows' GDI+ calls to draw and cannot draw on top of WPF.

If you didn't got an error when compiling the first line of your code, then probably your bitmapImg is a System.Drawing.Image (from WinForms) not an Image control from WPF (System.Window.Controls.Image).

As adrianm mentioned, the easiest way will probably be to use a Grid:

Then, in your click event handler you can make the line visible and give it the coordinates you want:

line.Visibility = Visible;
line.X1 = mouse_x;
line.Y1 = mouse_y;
line.X2 = ...;
line.Y2 = ...;