RFR: 8306707: Support pluggable image loading via javax.imageio [v18]

[Kevin Rushforth]

On Thu, 7 Nov 2024 19:04:07 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

>> This PR is an improved version of #1093.
>> 
>> JavaFX can load BMP, GIF, PNG, and JPEG images with its built-in image loaders. It has been a long-standing request to support more image formats, most notably (but not limited to) SVG. However, adding more built-in image loaders is a significant effort not only in creating the functionality, but also in maintaining the additional dependencies.
>> 
>> This will probably not happen any time soon, so we are left with three alternatives:
>> 1. Accept the fact that JavaFX will never be able to load additional image formats.
>> 2. Create a public image loader API, and hope that developers in the JavaFX ecosystem will create image loader plugins.
>> 3. Leverage the existing Java Image I/O API.
>> 
>> From these options, I think we should simply support existing Java APIs; both because it is the shortest and most realistic path forward, but also because I don't think it is sensible to bifurcate pluggable image loading in the Java ecosystem.
>> 
>> Of course, Java Image I/O is a part of the `java.desktop` module, which as of now, all JavaFX applications require. However, it has been noted in the previous PR that we shouldn't lock JavaFX into the `java.desktop` dependency even further.
>> 
>> I've improved this PR to not permanently require the `java.desktop` dependency: if the module is present, then JavaFX will use Image I/O for image formats that it can't load with the built-in loaders; if the module is not present, only the built-in loaders are available.
>> 
>> I have prepared a small sample application that showcases how the feature can be used to load SVG images in a JavaFX application: https://github.com/mstr2/jfx-imageio-sample
>
> Michael Strauß has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - move automatically added imports
>  - rename test...javax -> test...java2d

> This patch causes a failure in one of our closed white-box tests, which depends on internal API that has changed. It will be easy for us to fix it, but it will mean that down the road, when this is ready to go in, we will need to coordinate the timing of the integration with you.

I have a patch for our closed test that I've been using for testing. I ran a Jenkins headful test job and with that (closed) patch + the latest patch in this PR and all looks good.

I've looked over most of the code changes and it all looks good. I'll finish up next week.

@johanvos might want to review the changes in `IosImageLoader.java`

modules/javafx.graphics/src/main/java/com/sun/javafx/iio/png/PNGImageLoader2.java line 316:

> 314:                         : ImageStorage.ImageType.RGB;
> 315:             case PNG_COLOR_PALETTE:
> 316:                 return ImageStorage.ImageType.PALETTE;

Why was this case removed? Is it not used?

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PR Review: https://git.openjdk.org/jfx/pull/1593#pullrequestreview-2424642136
PR Review Comment: https://git.openjdk.org/jfx/pull/1593#discussion_r1834895733