RFR: 8306707: Support pluggable image loading via javax.imageio

[John Hendrikx]

On Tue, 15 Oct 2024 22:29:52 GMT, John Hendrikx <jhendrikx 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
>
> modules/javafx.graphics/src/main/java/com/sun/javafx/image/impl/BaseByteToByteConverter.java line 296:
> 
>> 294:         {
>> 295:             srcscanbytes -= w * 3;
>> 296:             srcscanbytes -= w * 4;
> 
> This really doesn't look right.  Should it not be `dstscanbytes` on the 2nd line, and also multiplied by `3` instead of `4`?
> 
> It looks like this was incorrect in the original?

Also nitpicking: I think it's bad form to modify parameter values.

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

PR Review Comment: https://git.openjdk.org/jfx/pull/1593#discussion_r1802105879