[Rev 02] RFR: 8238954: Improve performance of tiled snapshot rendering

[Ambarish Rapte]

On Mon, 9 Mar 2020 10:01:53 GMT, Frederic Thevenet <github.com+7450507+fthevenet at openjdk.org> wrote:

>> Issue JDK-8088198, where an exception would be thrown when trying to capture a snapshot whose final dimensions would be
>> larger than the running platform's maximum supported texture size, was addressed in openjfx14. The fix, based around
>> the idea of capturing as many tiles of the maximum possible size and re-compositing the final snapshot out of these, is
>> currently only attempted after the original, non-tiled, strategy has already failed. This was decided to avoid any risk
>> of regressions, either in terms of performances and correctness, while still offering some relief to the original
>> issue.  This follow-on issue aims to propose a fix to the original issue, that is able to correctly decide on the best
>> snapshot strategy (tiled or not) to adopt before applying it and ensure best performances possible when tiling is
>> necessary while still introducing no regressions compared to the original solution.
>
> Frederic Thevenet has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Avoid useless width and height calculation

The change seems good to me. Suggested few minor corrections and a query.

modules/javafx.graphics/src/main/java/com/sun/javafx/tk/quantum/QuantumToolkit.java line 1493:

> 1492:                 }
> 1493:                 else {
> 1494:                     rt.readPixels(buffer, rt.getContentX(), rt.getContentY(), w, h);

Please correct the `if` `else` formatting here and other places.

modules/javafx.graphics/src/main/java/com/sun/javafx/tk/quantum/QuantumToolkit.java line 1527:

> 1526:             private int computeOptimumTileSize(int size, int maxSize, AtomicBoolean isDivExact) {
> 1527:                 // This methods attempts to find the smallest integer divider for the provided `size`
> 1528:                 // while the result of the division is less than `maxSize`.

This **method** attempts to....

modules/javafx.graphics/src/main/java/com/sun/javafx/tk/quantum/QuantumToolkit.java line 1575:

> 1574:                         }
> 1575:                         // Find out it is is possible to divide up the image in tiles of the same size
> 1576:                         AtomicBoolean exactWidthDivFound = new AtomicBoolean(false);

Find out **if it** is possible...

modules/javafx.graphics/src/main/java/com/sun/javafx/tk/quantum/QuantumToolkit.java line 1600:

> 1599:                                 }
> 1600:                             }
> 1601:                         }

The `if (exactHeightDivFound.get())` and `else` block here look effectively same. Could you please take a re-look or
explain what am I missing here.

modules/javafx.graphics/src/main/java/com/sun/javafx/tk/quantum/QuantumToolkit.java line 1576:

> 1575:                         // Find out it is is possible to divide up the image in tiles of the same size
> 1576:                         AtomicBoolean exactWidthDivFound = new AtomicBoolean(false);
> 1577:                         int tileWidth = computeOptimumTileSize(w, maxTextureSize, exactWidthDivFound);

`exactWidthDivFound` is unused, may be can skip creating a named variable and just pass a unnamed `AtomicBoolean` in
next call to `computeOptimumTileSize`

-------------

Changes requested by arapte (Reviewer).

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