how to create a transparent rectangle responding to click event in Tkinter

Question

I need to draw a rectangle in a tkinter.canvas to respond click event:

click_area = self.canvas.create_rectangle(0,0,pa_width,pa_height,fill=\'LightBlue\',ou         


        

Answer 1

I came across this same issue trying to use the find_closest Canvas method to modify existing rectangles, but simply binding to the canvas didn't work. The issue is that a Tkinter rectangle without a fill will only respond to clicks on its border.

Then I read about the stipple argument to create_rectangle from here:

stipple: A bitmap indicating how the interior of the rectangle will be stippled.

Default is stipple="", which means a solid color. A typical value would be stipple='gray25'. Has no effect unless the fill has been set to some color. See Section 5.7, “Bitmaps”.

And the section on bitmaps states that only a few stipple options are available by default, but none of them are completely transparent. However, you can specify your own custom bitmap as an X bitmap image (a .xbm file).

XBM files are really just text files with a C-like syntax, so I made my own 2x2 bitmap with all transparent pixels and saved it as transparent.xbm in the same directory as my Tkinter script. Here's the code for the XBM file:

#define trans_width 2
#define trans_height 2
static unsigned char trans_bits[] = {
   0x00, 0x00
};

Then, you can specify the custom stipple by prefixing the xbm file name with a @ when creating your rectangle:

self.canvas.create_rectangle(
    x1,
    y1,
    x2,
    y2,
    outline='green',
    fill='gray',  # still needed or stipple won't work
    stipple='@transparent.xbm',
    width=2
)

Note, you still need to provided some fill value or the stipple will not be applied. The actual fill value doesn't matter as the stipple will "override" it in the canvas.