RFR: 8350917: Allow parent nodes to provide CSS styleable properties for child nodes

[Michael Strauß]

On Mon, 17 Feb 2025 01:15:37 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

> 8350917: Allow parent nodes to provide CSS styleable properties for child nodes

modules/javafx.graphics/src/main/java/javafx/css/Styleable.java line 101:

> 99:      * only for its direct children!
> 100:      *
> 101:      * @return an immutable list of CSS meta data, never {@code null}

Since we don't specify that `getCssMetaData()` should never return null, we should consider also not specifying it here. Alternatively, maybe we should add the non-null requirement to the existing `getCssMetaData()`.

modules/javafx.graphics/src/main/java/javafx/scene/CssStyleHelper.java line 465:

> 463:     }
> 464: 
> 465:     private record StylingContext(Node node, CalculatedValue font, StyleMap styleMap, Set<PseudoClass> pseudoClasses) {}

It might not be a good trade-off to create lots of transient objects on a hot path just to save a few arguments in the calling convention. This would be a nice improvement once we have value types in Java.

modules/javafx.graphics/src/main/java/javafx/scene/layout/Pane.java line 128:

> 126:         @SuppressWarnings("unchecked")
> 127:         StyleableObjectProperty<T> castProperty = (StyleableObjectProperty<T>) child.getProperties()
> 128:             .computeIfAbsent(cssMetaData, k -> createChildConstraintProperty(child, cssMetaData));

Since we're on a hot path here, I'd like to see this work without unnecessary memory allocations:
1. Check `hasProperties()` before calling `getProperties()`.
2. Don't use `computeIfAbsent()` since it requires a capturing lambda.

modules/javafx.graphics/src/main/java/javafx/scene/layout/Pane.java line 140:

> 138:         }
> 139: 
> 140:         String propertyName = name + " (parent property)";

I think a more sensible naming scheme would be something like "VBox.margin", which should be supplied as an argument and not generated on the fly.

modules/javafx.graphics/src/main/java/javafx/scene/layout/Pane.java line 234:

> 232:             }
> 233: 
> 234:             if (value != null) {

How would the value ever be anything other than a `StyleableObjectProperty`, since `setChildConstraint()` always creates a `StyleableObjectProperty`?

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PR Review Comment: https://git.openjdk.org/jfx/pull/1714#discussion_r1997679699
PR Review Comment: https://git.openjdk.org/jfx/pull/1714#discussion_r1997663655
PR Review Comment: https://git.openjdk.org/jfx/pull/1714#discussion_r1997683419
PR Review Comment: https://git.openjdk.org/jfx/pull/1714#discussion_r1997682667
PR Review Comment: https://git.openjdk.org/jfx/pull/1714#discussion_r1997684595