[Rev 03] RFR: 8238954: Improve performance of tiled snapshot rendering

[Frederic Thevenet]

On Tue, 17 Mar 2020 14:19:45 GMT, Frederic Thevenet <github.com+7450507+fthevenet at openjdk.org> wrote:

>> Now that the tiling is done in the `QuantumRenderer` level, I'll bring back
>> [JDK-8189082](https://bugs.openjdk.java.net/browse/JDK-8189082). Can't this tiling be used to fix that?
>
>> 
>> 
>> Now that the tiling is done in the `QuantumRenderer` level, I'll bring back
>> [JDK-8189082](https://bugs.openjdk.java.net/browse/JDK-8189082). Can't this tiling be used to fix that?
> 
> It won't help with thing in their current state, as the `RenderToImage` method that is modified in this PR is currently
> called only by the snapshot feature in `Scene` But of course I suspect the same technique could also be used to solve
> [JDK-8189082](https://bugs.openjdk.java.net/browse/JDK-8189082) and now is indeed a good time to investigate it
> further. I'll have a look to see if it is possible to factorize the tiling implementation for both classes of issues,
> in which case it would make sense to do prior to merging this PR. If it is different enough that the implementation
> cannot be shared but only the general idea, then I suggest we address it in a different PR.  What do you all think ?

At first glance, the NPE in [JDK-8189082](https://bugs.openjdk.java.net/browse/JDK-8189082) occurs in the Prism layer,
which is one level _below_ Quantum where the tiling is currently implemented, so I'm not sure tit is reachable from
there; if we want the code to be shared, it looks like it would need to be moved even further down (maybe in the
`ResourceFactory`?)

Also, while reusing code is generally the way to go, in such lower layers, very closely intertwined with the actual
rendering, I'm afraid that insisting on having a "one-size-fits-all" implementation might get in the way of necessary
case-by-case optimizations, so I'd like to have someone with a deeper knowledge  of the code base to weight in before
starting work in that direction. Maybe @kevinrushforth could advise?

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PR: https://git.openjdk.java.net/jfx/pull/112