RFR: 8372530: Easier placement of windows with positioning anchor

[Andy Goryachev]

On Tue, 25 Nov 2025 18:58:14 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

> This enhancement allows `Stage` to be placed on the screen similar to a popup window, where a user-specified positioning anchors defines a point on the stage that should coincide with a given location on the screen. For this purpose, the following new methods are added to `Stage`:
> 
> 
> public class Stage {
>     public void relocate(AnchorPoint screenAnchor, AnchorPoint stageAnchor);
>     public void relocate(AnchorPoint screenAnchor, Insets screenPadding, AnchorPoint stageAnchor, AnchorPolicy);
>     public void relocate(Screen, AnchorPoint screenAnchor, Insets screenPadding, AnchorPoint stageAnchor, AnchorPolicy);
> }
> 
> 
> ## AnchorPoint
> `AnchorPoint` is a point that is either specified in absolute coordinates, or relative to the screen or stage:
> 
> var anchor1 = AnchorPoint.proportional(0.5, 0.5); // center of the screen/stage
> var anchor2 = AnchorPoint.absolute(100, 100); // absolute coordinates within screen/stage
> 
> 
> For example, a stage that sits flush with the bottom-right corner of the screen can be shown as follows:
> 
> var screenAnchor = AnchorPoint.proportional(1, 1); // or use the AnchorPoint.BOTTOM_RIGHT constant
> var stageAnchor = AnchorPoint.proportional(1, 1);
> stage.relocate(screenAnchor, stageAnchor);
> stage.show();
> 
> 
> ## AnchorPolicy
> `AnchorPolicy` controls how the anchor may be adjusted when the preferred placement doesn't fit within the screen bounds:
> 
> 
> public enum AnchorPolicy {
>     FIXED,
>     FLIP_HORIZONTAL,
>     FLIP_VERTICAL,
>     AUTO
> }
> 
> 
> * `FIXED`: always use the provided anchor; only adjust the resulting position to fit within the screen.
> * `FLIP_HORIZONTAL`: if the preferred placement violates horizontal constraints, try a horizontally flipped anchor (e.g. top-left to top-right) before falling back to the original anchor.
> * `FLIP_VERTICAL`: likewise for vertical constraints.
> * `AUTO`: automatically choose the most suitable flip:
>    if only horizontal constraints are violated, acts like `FLIP_HORIZONTAL`;
>    if only vertical constraints are violated, acts like `FLIP_VERTICAL`;
>    if both are violated, try a diagonally flipped anchor (both axes) and pick the placement that requires the least adjustment.
> 
> This is useful for popup-like behavior where you have a preferred "opening direction", but want the window to flip to the opposite side of the reference point when there isn’t enough space (e.g. "prefer below, but open above if below doesn’t fit").
> 
> ### PopupWindow support
> The new `PopupWindow.anchorPolicy` property adds the same "flip the anchor when it...

modules/javafx.graphics/src/main/java/com/sun/javafx/stage/WindowRelocator.java line 105:

> 103:             } else {
> 104:                 gravityX = stageAnchor.getX() / windowWidth;
> 105:                 gravityY = stageAnchor.getY() / windowHeight;

It might be a good idea to explain what "gravity" is, maybe in `ComputedLocation` or `WindowLocationAlgorithm`.

Here, for example, L101 tells us the gravity is measured in pixels, while L104 indicates the gravity is dimensionless.

modules/javafx.graphics/src/main/java/javafx/stage/Stage.java line 1322:

> 1320:      * @since 26
> 1321:      */
> 1322:     public final void relocate(Screen screen, AnchorPoint screenAnchor, Insets screenPadding,

would it be conceptually simpler to offer just one new method with all the possible parameters (screen anchors, insets) instead of several?  I presume these new methods will be rarely used.
or, if there is one frequent case, provide an additional utility method for that case?

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

PR Review Comment: https://git.openjdk.org/jfx/pull/1986#discussion_r2608315565
PR Review Comment: https://git.openjdk.org/jfx/pull/1986#discussion_r2608469098