RFR: 8318364: Add an FFM-based implementation of harfbuzz OpenType layout

[Jorn Vernee]

On Tue, 29 Aug 2023 22:04:40 GMT, Phil Race <prr at openjdk.org> wrote:

> 8318364: Add an FFM-based implementation of harfbuzz OpenType layout

src/java.desktop/share/classes/sun/font/HBShaper.java line 310:

> 308:         SequenceLayout glyphInfosLayout = MemoryLayout.sequenceLayout(maxinfo, GlyphInfoLayout);
> 309:         codePointHandle = getVarHandle(glyphInfosLayout, "codepoint");
> 310:         clusterHandle = getVarHandle(glyphInfosLayout, "cluster");

There are better ways to do this in the latest API, by using the extra offset parameter and `MemoryLayout::scaleHandle`.

I suggest changing this to:

Suggestion:

        x_offsetHandle = getVarHandle(PositionLayout, "x_offset");
        y_offsetHandle = getVarHandle(PositionLayout, "y_offset");
        x_advanceHandle = getVarHandle(PositionLayout, "x_advance");
        y_advanceHandle = getVarHandle(PositionLayout, "y_advance");
        codePointHandle = getVarHandle(GlyphInfoLayout, "codepoint");
        clusterHandle = getVarHandle(GlyphInfoLayout, "cluster");


And then in `getVarHandle`:


    private static VarHandle getVarHandle(MemoryLayout enclosing, String name) {
        VarHandle h = layout.varHandle(PathElement.groupElement(name));
        // scale offset by the size of 'enclosing'
        h = MethodHandles.collectCoordinates(h, 1, enclosing.scaleHandle());
        /* insert 0 offset so don't need to pass arg every time */
        return MethodHandles.insertCoordinates(h, 1, 0L).withInvokeExactBehavior();
    }


(hope I eyeballed that correctly...)

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PR Review Comment: https://git.openjdk.org/jdk/pull/15476#discussion_r1361989861