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Editorial Team
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Asked: 2026-06-02T20:28:02+00:00

I want to make something akin to a diagram editor – an application that

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I want to make something akin to a diagram editor – an application that allows the user to create, view and edit a bunch of shapes on a canvas. My GUI has essentially three parts – a standard JMenuBar, one JPanel on the right side for showing info about the shapes and a JPanel next to it that should be used for visualizing the shapes.

Aside from that, I have a package that defines the shapes. For simplicity’s sake say there is just a Square, containing the following information: coordinates on the canvas, size, user-defined name and description, color.
The main class of the project (an extension of JFrame) contains lists of Squares.

Now, I could visualize the shapes by simply drawing them in the JPanel using drawrect and whatnot, but I want to create an interactive editor – if the user right-clicks on a visualized shape, a context menu would pop-up allowing him to move it, change its properties or remove the shape altogether. Clicking an empty spot in the JPanel would allow the user (again, via a menu) to create a new shape.

Is there an automated way to do this as opposed to manually keeping a matrix mapping each pixel of the canvas to a certain shape and checking it upon right click? One where I could say, for example, draw this here within the JPanel and do something onclick…
A related question, when I edit the shape in the JPanel, how do I access the Square/Circle list in the main application class, so that I can really change it? I suppose this is simple, but right now I don’t know how I would do it.

Please point me in the right direction, anything will be appreciated, tips, examples, links to relevant tutorials…

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1 Answer

  1. Editorial Team

    The most common way to accomplish this is to allow shapes to determine if point is inside the shape. Hopefully your code is object oriented and each type of your shape is a class.

    All you have to do is to define a method such as boolean isInside( point: Point) for each shape. Once you have those all you have to do is walk the shapes in the reverse z-order (from top to bottom) and and see where the mouse click point lends. If it does not lend on any shape – you clicked the canvas. Once you have this info you can show an appropriate menu.

    Hope this helps

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