RFR: 8372530: Easier placement of windows with positioning anchor

[Marius Hanl]

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...

I will test and review this. Especially test with the scenarios where I used the workaround described in the mailing list. 
And give feedback accordingly (API and Functionality-wise).
Will probably take a bit, as there are some other things (like Direct3D12) on my list.

modules/javafx.graphics/src/main/java/javafx/stage/Stage.java line 1298:

> 1296:     @Override
> 1297:     public void centerOnScreen() {
> 1298:         relocationRequest = null; // cancel previous relocation request

As far as I understand, with the new anchor system, a center on screen can easily be achieved as well? I wonder if we could also deprecate this method instead. But not sure if I understand it correctly.

modules/javafx.graphics/src/main/java/javafx/stage/Stage.java line 1459:

> 1457:      * @since 26
> 1458:      */
> 1459:     public static final class Anchor {

This could be a record too

modules/javafx.graphics/src/main/java/javafx/stage/Window.java line 1120:

> 1118:                     }
> 1119: 
> 1120:                     // Give subclasses a chance to adjust the window bounds

Unrelated to this Enhancement, but I wonder if the `centerOnScreen` line before could also be rewritten using this system (at one point). Now, it looks like he might be centering the `Window`, and then fix the bounds to something else, wasting some time.

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

PR Comment: https://git.openjdk.org/jfx/pull/1986#issuecomment-3585241787
PR Review Comment: https://git.openjdk.org/jfx/pull/1986#discussion_r2570081956
PR Review Comment: https://git.openjdk.org/jfx/pull/1986#discussion_r2563846982
PR Review Comment: https://git.openjdk.org/jfx/pull/1986#discussion_r2563859678