Can anyone help or point me in the right direction for figuring out how to create a drag and draw rectangular box to be used as a selection tool in PyGtk? I am presently using an event box with a drawable window and the user can click once in the upper left and once in the lower right corner of the portion of image they would like to choose which will then draw a rectangle over the selection, but a drag and draw rectangle will allow the user to better adjust and get better accuracy.
I have looked quite a few places for information or a tutorial on this but I haven’t found much. I am relatively new to Gtk+ so perhaps this is so simple that no one has to ask.
Actually, this doesn’t seem all that lamebrained at all. It is actually quite specific, and a little challenging.
I’ll give you the steps to start you off, but as you’re beginning (and you didn’t post any specific code), it would be better for you to create the code yourself based on documentation and my hints.
By the way, look up the official PyGTK documentation – that should be your definitive source for all the objects and functions of PyGTK. It is very well written and exhaustive, and I rarely have to look more than five minutes to find what I need.
What I suggest you do is use three signals, connected to your drawing area.
Create three callbacks (tutorial here), one for each event. Connect your drawing area to your events and callbacks (again, see tutorial. You may need to go through a few pages on it.).
You are going to also need to create two boolean variables on the global level (above the main class, at the same level you import modules.) The first controls whether the selection tool is chosen (call it “Select_On”), and the second for if it is active (call it “Select_Active”)
On the button you use to start the select tool, set “Select_On” to “True”. This should probably be a toggle button, so make sure you set it up so “Select_On” gets set to off if you toggle the button off.
On button-press-event, create the object for selecting. What you’re going with now actually should work well. Also, set “Select_Active” to “True”.
On motion-notify-event, change the size of your object based on cursor position. Refer to that documentation for that particular kind of object to learn how to change its size, and refer here for how to get the cursor position.
Be prepared to write an algorithm to determine how to change the size of the selection object based on the cursor position. If you need help with that, feel free to ask for it in a separate question.
On button-release-event, set “Select_Active” to “False”, and call all your code for actually confirming the selection.
As an aside, the benefit to using the “motion-notify-event” is that, as soon as the cursor leaves the widget you’re selection in, the selection box stops changes sizes. The cursor must re-enter the widget to continue changing the selection box size.
I hope all that works for you, and wishing you the very best on your project!