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Noticable on macintosh: Scroll the editor with the mouse wheel, quickly, over a large file. You will see the code folding bar get painted once with the gray window background color, and then overpainted with its contents. This definitely slows down scrolling.
Code folding side bar signs are painted. It is not image, because the signs need to be resized in accordance with fontsize change. The fill if required for side bar background coloring. The same mechanism is used also in glyph gutter. There is only one repaint operation call during one scroll. Fill operation is not time consuming. CodeFoldingSideBar just overrides JComponent.paintComponent, where in parent paintComponent method is also filling the component with background color. I am closing this as wontfix.
Then override Component.update() to do nothing - what's happening is, when scrolling on mac-os, it is flushed twice - once with gray, and again with the background color. It looks very bad, and it definitely does affect performance when paints are being flushed direct to the screen (no double buffering) when scrolling. When not scrolling, I agree with you, it's no big deal.
Unfortunatelly I cannot reproduce the problem. But I have overriden Component.update() to do nothing as you suggested. (BTW, on winXP the method "update" is never called during scrolling or painting.) But perhaps this vary on OS and causes problem on Mac. Could you please verify the fix? Thanks. /cvs/editor/libsrc/org/netbeans/editor/CodeFoldingSideBar.java,v <-- CodeFoldingSideBar.java new revision: 1.23; previous revision: 1.22