[FIXED] JavaFX: how to clear a drawing without affecting background

Issue

Very simple question, but I could not find the answer in JavaFX docs or StackOverflow:

I have a JavaFX Canvas filled with a graph (various calls to strokeLine(), not the issue here). I need to be able to draw a rectangle over this graph, then simply clear the rectangle, without affecting the graph in the background. (Like an undo operation).

Code to draw the rectangle ('p' and 'e' are points):

gc.rect(p.getX(), p.getY(), e.getX()-p.getX(), e.getY()-p.getY());
gc.stroke();

The most obvious answer would be to use the clearRect() method, but the problem is that it clears also the portion of the graph in the background...

So the question is: how do I clear a drawing that was made with stroke(), without affecting the other drawings in the background?

Solution

You can't do this with one canvas.

Canvas only store the result of your painting operation. This is the interest of the canvas you can stroke million times the same line and it will only store and represent the result and doesn't consume more memory.

So you if you need to draw Something over your chart you should put an other canvas over the chart and draw on the second canvas.

Answered By - user43968
Answer Checked By - Katrina (JavaFixing Volunteer)