Determining the visible lines of a JEditorPane within a JScrollPane

Question

I need to track what lines are visible (the Document line numbers) within the Viewport of a JScrollPane that contains a JEditorPane. Is this achievable?

Answer 1

That's a tricky one.
Maybe something like this:
First get the view coordinate of the top left corner of the view port
Point p = scrollPane.getViewPort().getViewPosition();Then convert that view location into a model location. The model location will be an index into the document.
int modelLocation = editorPane.viewToModel( p );Now you just need to count how many lines are before this index location. As I recall there is a main root element for the whole document. The root element is made up of child elements, one for each line. This may be different for HTML but might work for text or rich text.
Element rootElement = editorPane.getDocument().getRootElements()[0];
// getElementIndex() will give you the child element index (e.g. line element that is at the given document location).
int lines = rootElement.getElementIndex( modelLocation );Do the same for the point location that is at the viewport's location plus the viewport's size (i.e. the lower right corner of the viewport).
There is a LOT of speculation here since I haven't actually put this to a test case. But maybe its enough to point you in a direction that works.
-Mike