On Thu, 4 Jul 2024 19:40:57 GMT, Michael Strauß <mstra...@openjdk.org> wrote:
>> This PR completes the CSS Transitions story (see #870) by adding
>> interpolation support for backgrounds and borders, making them targetable by
>> transitions.
>>
>> `Background` and `Border` objects are deeply immutable, but not
>> interpolatable. Consider the following `Background`, which describes the
>> background of a `Region`:
>>
>>
>> Background {
>> fills = [
>> BackgroundFill {
>> fill = Color.RED
>> }
>> ]
>> }
>>
>>
>> Since backgrounds are deeply immutable, changing the region's background to
>> another color requires the construction of a new `Background`, containing a
>> new `BackgroundFill`, containing the new `Color`.
>>
>> Animating the background color using a CSS transition therefore requires the
>> entire Background object graph to be interpolatable in order to generate
>> intermediate backgrounds.
>>
>> More specifically, the following types will now implement `Interpolatable`.
>>
>> - `Insets`
>> - `Background`
>> - `BackgroundFill`
>> - `BackgroundImage`
>> - `BackgroundPosition`
>> - `BackgroundSize`
>> - `Border`
>> - `BorderImage`
>> - `BorderStroke`
>> - `BorderWidths`
>> - `CornerRadii`
>> - `ImagePattern`
>> - `LinearGradient`
>> - `RadialGradient`
>> - `Stop`
>>
>> ## Interpolation of composite objects
>>
>> As of now, only `Color`, `Point2D`, and `Point3D` are interpolatable. Each
>> of these classes is an aggregate of `double` values, which are combined
>> using linear interpolation. However, many of the new interpolatable classes
>> comprise of not only `double` values, but a whole range of other types. This
>> requires us to more precisely define what we mean by "interpolation".
>>
>> Mirroring the CSS specification, the `Interpolatable` interface defines
>> several types of component interpolation:
>>
>> | Interpolation type | Description |
>> |---|---|
>> | default | Component types that implement `Interpolatable` are interpolated
>> by calling the `interpolate(Object, double)}` method. |
>> | linear | Two components are combined by linear interpolation such that `t
>> = 0` produces the start value, and `t = 1` produces the end value. This
>> interpolation type is usually applicable for numeric components. |
>> | discrete | If two components cannot be meaningfully combined, the
>> intermediate component value is equal to the start value for `t < 0.5` and
>> equal to the end value for `t >= 0.5`. |
>> | pairwise | Two lists are combined by pairwise interpolation. If the start
>> list has fewer elements than the target list, the missing elements are
>> copied from the target li...
>
> 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 13 additional
> commits since the last revision:
>
> - fix line separators
> - add documentation to Point2D/3D
> - change documentation
> - add specification
> - add exports
> - revert change
> - revert change
> - added more tests
> - added specification and tests
> - Merge branch 'master' into feature/interpolatable
> - ... and 3 more: https://git.openjdk.org/jfx/compare/60cc590f...08ed751b
modules/javafx.graphics/src/main/java/javafx/scene/paint/Stop.java line 267:
> 265: public Stop(@NamedArg("offset") double offset,
> @NamedArg(value="color", defaultValue="BLACK") Color color) {
> 266: this.offset = offset;
> 267: this.color = Objects.requireNonNullElse(color,
> Color.TRANSPARENT);
Note that a `null` color is now treated as `TRANSPARENT` for the following
reasons:
1. The previous implementation was broken: if a `Stop` is constructed with a
`null` color, the `hashCode()` method throws a NPE because it doesn't check for
`null`.
2. It doesn't make sense to have a stop with `null` color. What does it even
mean?
3. When the stop list is normalized, an empty or null list is treated as a
two-stop list with `TRANSPARENT` color (see `normalize()`). So we already have
a scenario where `null` is treated as `TRANSPARENT`.
-------------
PR Review Comment: https://git.openjdk.org/jfx/pull/1471#discussion_r1666040056
