Easy way to check if SVG is supported by SWT

[ptziegler]

For the next release, we'd like to consume some of our SVG-based icons in the GEF project directly, rather than their PNG counterpart. But to remain compatible with older Eclipse releases, we need to check whether this is supported by the SWT version of the running application.

My current ideas are:

• to check whether the org.eclipse.swt.svg fragment is active (e.g. via Platform.getBundle())
• to check whether there is any active bundle providing the SVG capability
• to check whether the SVGRasterizer class exists (via reflection) and then assume that there is a matching implementation
• to try and load a "dummy" SVG and treat an exception as "unsupported"...

The first two are not really possible for Draw2D as it may be executed without OSGi and the latter are not very clean, either. So my question: Does SWT have an easy way to check whether the SVG (or any given file format) is currently supported?

[ptziegler]

To answer my own question: SVG support can be required via the following entry in the manifest header:

Require-Capability: eclipse.swt;filter:="(image.format=svg)";resolution:=optional

This capability must be marked as optional, to remain backwards compatible. To then check whether SVG is supported, following snippet can be used:

private static Boolean isSvgSupported;

public static boolean isSvgSupported() {
    if (isSvgSupported != null) {
        return isSvgSupported;
    }

    isSvgSupported = false;
    BundleWiring wiring = FrameworkUtil.getBundle(InternalGEFPlugin.class).adapt(BundleWiring.class);
    if (wiring == null) {
        return false;
    }

    List<BundleRequirement> requirements = wiring.getRequirements("eclipse.swt"); //$NON-NLS-1$
    for (BundleRequirement requirement : requirements) {
        String filter = requirement.getDirectives().get(Constants.FILTER_DIRECTIVE);
        if ("(image.format=svg)".equals(filter)) { //$NON-NLS-1$
            isSvgSupported = true;
            break;
        }
    }
    return isSvgSupported;
}

Though this only works if used with OSGi. Otherwise something like a system property must be used...

[HannesWell]

For non-OSGi runtime you could also check if you could obtain an implementation of the SVGRasterizer. This would then be one step further than your third suggestion "to check whether the SVGRasterizer class exists".
In OSGi runtime this could be difficult as the o.e.swt.svg fragment is lacking the required OSGi ServiceLoader mediator headers.

Please also keep in mind that SVGRasterizer is internal.

[ptziegler]

For non-OSGi runtime you could also check if you could obtain an implementation of the SVGRasterize

Good point, I didn't notice the SPI service. Thanks!

Please also keep in mind that SVGRasterizer is internal.

So there's no official way to contribute your own SVG rasterizer?

[laeubi]

I think the best way is really to load an (empty) SVG image and check if it gives an error.

Beside that I already suggested elsewhere that we probably should just first check for an svg file and use that even if a png is requested. That way one don't need to rewrite all code, but just supply a fragment with svgs to any plugin.