RFR: 8264591: HBox/VBox child widths pixel-snap to wrong value [v2]

[Michael Strauß]

> The children of HBox/VBox don't always pixel-snap to the same value as the container itself when a render scale other than 1 is used. This can lead to a visual glitch where the content bounds don't line up with the container bounds. In this case, the container will extend beyond its content, or vice versa.
> 
> The following program shows the problem for HBox:
> 
> Region r1 = new Region();
> Region r2 = new Region();
> Region r3 = new Region();
> Region r4 = new Region();
> Region r5 = new Region();
> Region r6 = new Region();
> r1.setBackground(new Background(new BackgroundFill(Color.GREY, null, null)));
> r2.setBackground(new Background(new BackgroundFill(Color.DARKGRAY, null, null)));
> r3.setBackground(new Background(new BackgroundFill(Color.BLACK, null, null)));
> r4.setBackground(new Background(new BackgroundFill(Color.GREY, null, null)));
> r5.setBackground(new Background(new BackgroundFill(Color.DARKGRAY, null, null)));
> r6.setBackground(new Background(new BackgroundFill(Color.BLACK, null, null)));
> r1.setPrefWidth(25.3);
> r2.setPrefWidth(25.3);
> r3.setPrefWidth(25.4);
> r4.setPrefWidth(25.3);
> r5.setPrefWidth(25.3);
> r6.setPrefWidth(25.4);
> r1.setMaxHeight(30);
> r2.setMaxHeight(30);
> r3.setMaxHeight(30);
> r4.setMaxHeight(30);
> r5.setMaxHeight(30);
> r6.setMaxHeight(30);
> HBox hbox1 = new HBox(r1, r2, r3, r4, r5, r6);
> hbox1.setBackground(new Background(new BackgroundFill(Color.RED, null, null)));
> hbox1.setPrefHeight(40);
> 
> r1 = new Region();
> r2 = new Region();
> r3 = new Region();
> r4 = new Region();
> r5 = new Region();
> r6 = new Region();
> r1.setBackground(new Background(new BackgroundFill(Color.GREY, null, null)));
> r2.setBackground(new Background(new BackgroundFill(Color.DARKGRAY, null, null)));
> r3.setBackground(new Background(new BackgroundFill(Color.BLACK, null, null)));
> r4.setBackground(new Background(new BackgroundFill(Color.GREY, null, null)));
> r5.setBackground(new Background(new BackgroundFill(Color.DARKGRAY, null, null)));
> r6.setBackground(new Background(new BackgroundFill(Color.BLACK, null, null)));
> r1.setPrefWidth(25.3);
> r2.setPrefWidth(25.3);
> r3.setPrefWidth(25.4);
> r4.setPrefWidth(25.3);
> r5.setPrefWidth(25.3);
> r6.setPrefWidth(25.4);
> r1.setMaxHeight(30);
> r2.setMaxHeight(30);
> r3.setMaxHeight(30);
> r4.setMaxHeight(30);
> r5.setMaxHeight(30);
> r6.setMaxHeight(30);
> HBox hbox2 = new HBox(r1, r2, r3, r4, r5, r6);
> hbox2.setBackground(new Background(new BackgroundFill(Color.RED, null, null)));
> hbox2.setPrefHeight(40);
> hbox2.setPrefWidth(152);
> 
> VBox root = new VBox(new HBox(hbox1), new HBox(hbox2));
> root.setSpacing(20);
> Scene scene = new Scene(root, 500, 250);
> 
> primaryStage.setScene(scene);
> primaryStage.show();
> 
> 
> Here's a before-and-after comparison of the program above after applying the fix. Note that 'before', the backgrounds of the container (red) and its content (black) don't align perfectly. The render scale is 175% in this example.
> ![pixel-glitch](https://user-images.githubusercontent.com/43553916/112891996-146e2d80-90d9-11eb-9d83-97754ae38dc1.png)
> 
> I've filed a bug report and will change the title of the GitHub issue as soon as it's posted.

Michael Strauß has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - added documentation, improved method names
 - Merge branch 'master' into fixes/box-snap-to-pixel
 - Fix pixel-snapping glitches in VBox/HBox
 - Failing test

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

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/445/files
  - new: https://git.openjdk.java.net/jfx/pull/445/files/c218b809..744f19f5

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=445&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=445&range=00-01

  Stats: 449813 lines in 8109 files changed: 251439 ins; 126257 del; 72117 mod
  Patch: https://git.openjdk.java.net/jfx/pull/445.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/445/head:pull/445

PR: https://git.openjdk.java.net/jfx/pull/445