Are you able to test on platforms other than macOS? (I’m not, so I can’t help with that.)
Alan > On Jun 7, 2023, at 10:53 AM, Jeremy <[email protected]> wrote: > > # Problem Summary > > For non-opaque windows, Window#paint calls `gg.fillRect(0, 0, getWidth(), > getHeight())` before `super.paint(g)`. > > This can cause flickering on Mac, and the flickering seems to have gotten > much worse in recent JVMs. (See movie attachments to original ticket.) > > # Discussion > > This is my 2nd PR for this ticket. The original is > [here](https://github.com/openjdk/jdk/pull/12993); that proposed change was > IMO more invasive/scarier. It was auto-closed after 8 weeks of inactivity, > and I'd rather offer this PR instead. > > In that previous discussion Alan Snyder framed the core problem as a "lack of > synchronization" (see [comment > here](https://github.com/openjdk/jdk/pull/12993#issuecomment-1467528061)). If > the monitor refreshes/flushes after we've called `fillRect` *but before we > finish `super.paint`*: it makes sense that we'd see a flicker. > > I agree with Alan, but I think the problem can also be framed as a > mixing-Swing-with-AWT issue. (Which IMO will involve an easier fix.) > > This PR is a low-risk change (relative to the previous PR) that intercepts > calls to repaint a Window that is also RootPaneContainer. Now we'll redirect > those calls to paint the JRootPane instead. This means we'll exclusively > paint within Swing's/RepaintManager's double-buffered architecture, so we > bypass the risky call to `fillRect` on the screen's Graphics2D. (And this > change occurs within RepaintManager, so we're clearly already in Swing's > architecture.) > > So with this change: we paint everything to the double-buffer, and the *only > time* we paint to the Window's Graphics2D is when have set up a > AlphaComposite.Src and replace its contents with our buffer's contents. > > # Tests > > This PR includes a new test for 8303950 itself. This is pretty > self-explanatory: we repaint a trivial animation for a few seconds and use > the Robot to see if a pixel is the expected color. > > This PR also includes a test called `bug8303950_legacyWindowPaintBehavior` > that creates a grid of 4 windows with varying opacity/backgrounds: > > <img width="805" alt="image" > src="https://github.com/openjdk/jdk/assets/7669569/497c21a0-ed18-413f-a5c7-3ea146644fd6";> > > I was surprised by how these windows rendered, but I don't think that's worth > debating here. This test simply makes sure that we preserve this preexisting > behavior. The broad "rules" appear to be: > 1. If a JComponent identifies as opaque (see `JComponent.isOpaque`) then the > JComponent's background is used. (In this case: that's the opaque green top > two windows.) This is probably coming from `ComponentUI.update` > 2. If a JRootPane has a translucent background, that color "wins". It doesn't > composite on top of a window's translucent background: it simply *replaces* > it. (See the blue-ish bottom-right window. Note it's blue -- not purple.) > This is probably because the RepaintManager uses `AlphaComposite.Src` in a > couple of places to replace its destination Graphics. > 3. If a JRootPane has a null background color, then the Window's background > color paints as expected. (See the red-ish bottom-left window.) > > ------------- > > Commit messages: > - 8303950: working on occasional unit failures > - 8303950: avoid System.exit(1) > - 8303950: adding opaque white window under test windows > - 8303950: this resolves bug8303950 by adding special RootPaneContainer > behavior > - 8303950: adding unit test for legacy window behavior > - 8303950: fixing false negative > - 8303950: adding failing test to identify problem > - Merge pull request #4 from openjdk/master > - Merge pull request #3 from openjdk/master > - Merge pull request #2 from openjdk/master > - ... and 1 more: https://git.openjdk.org/jdk/compare/98a7a60f...37834391 > > Changes: https://git.openjdk.org/jdk/pull/14363/files > Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14363&range=00 > Issue: https://bugs.openjdk.org/browse/JDK-8303950 > Stats: 409 lines in 3 files changed: 407 ins; 1 del; 1 mod > Patch: https://git.openjdk.org/jdk/pull/14363.diff > Fetch: git fetch https://git.openjdk.org/jdk.git pull/14363/head:pull/14363 > > PR: https://git.openjdk.org/jdk/pull/14363 >
