RFR: 8322619: Parts of SG no longer update during rendering - overlapping - culling - dirty [v5]

[Florian Kirmaier]

On Fri, 3 May 2024 10:23:27 GMT, Florian Kirmaier <fkirmaier at openjdk.org> wrote:

>> In some situations, a part of the SG is no longer rendered.
>> I created a test program that showcases this problem.
>> 
>> Explanation:
>> 
>> This can happen, when a part of the SG, is covered by another Node.
>> In this part, one node is totally covered, and the other node is visible.
>> 
>> When the totally covered Node is changed, then it is marked dirty and it's parent, recursively until an already dirty node is found.
>> Due to the Culling, this totally covered Node is not rendered - with the effect that the tree is never marked as Clean.
>> 
>> In this state, a Node is Dirty but not It's parent. Based on my CodeReview, this is an invalid state which should never happen.
>> 
>> In this invalid state, when the other Node is changed, which is visible, then the dirty state is no longer propagated upwards - because the recursive "NGNode.markTreeDirty" algorithm encounters a dirty node early.
>> 
>> This has the effect, that any SG changes in the visible Node are no longer rendered. Sometimes the situation repairs itself.
>> 
>> Useful parameters for further investigations:
>> -Djavafx.pulseLogger=true
>> -Dprism.printrendergraph=true
>> -Djavafx.pulseLogger.threshold=0
>> 
>> PR:
>> This PR ensures the dirty flag is set to false of the tree when the culling is used.
>> It doesn't seem to break any existing tests - but I'm not sure whether this is the right way to fix it.
>> It would be great to have some feedback on this solution - maybe guiding me to a better solution.
>> 
>> I could write a test, that just does the same thing as the test application, but checks every frame that these nodes are not dirty - but maybe there is a better way to test this.
>
> Florian Kirmaier has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - JDK-8322619: Add test
>  - Revert "JDK-8322619: Clear dirty flag on the node and all its children if they are skipped due to visible==false or opacity==0"
>    
>    This reverts commit 5f9f1574515c078c1fd0dccd476325090a0b284d.

Sorry for creating the CSR, it was an accident.

Now that Eduard has both created an alternative solution, but also has reviewed that this solution is correct, and provided an unit-test - I think this (or the other) PR is ready to move forwards.

@kevinrushforth 
What do you think?

This is still quite a fundamental bug which is probably quite prevalent, 
because when it happens it is really hard to notice it.
But it probably happens more often than we think.

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PR Comment: https://git.openjdk.org/jfx/pull/1310#issuecomment-2117507318