[OpenJDK 2D-Dev] [PATCH] Make automatic font substitution on macOS work for surrogate pairs

[Dmitry Batrak]

Sure, here's the simplest test, that can be used for visual inspection:

import javax.swing.*;
import java.awt.*;

public class SurrogatesFallbackTest {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            JFrame frame = new JFrame();
            JLabel label = new JLabel(new
String(Character.toChars(0x1d400))); // MATHEMATICAL BOLD CAPITAL A
            label.setFont(new Font("Menlo", Font.PLAIN, 36)); // expected
to fallback to STIXGeneral
            frame.add(label);
            frame.pack();
            frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        });
    }
}

I can convert it to an automatic test (rendering to a bitmap and comparing
the result to rendering of 'missing' glyph), and add it to the webrev, if
that makes sense.

Best regards,
Dmitry Batrak

On Thu, Oct 27, 2016 at 2:17 AM, Philip Race <philip.race at oracle.com> wrote:

> Hi,
>
> I can file a bug on this if I can't find one.
> If you can email me the test it will help even if it is not checked in.
>
> -phil.
>
> On 10/26/16, 6:28 AM, Dmitry Batrak wrote:
>
> Hello,
>
> I'd like to propose a patch to make automatic font substitution on macOS
> work for surrogate pairs.
> I have a Contributor status via agreement signed by JetBrains, hope
> someone can sponsor the patch.
>
> Currently, if requested font cannot render a Unicode character represented
> by a surrogate pair,
> no substitution is performed - Font.canDisplay will return false, and the
> character will be
> rendered as a 'missing' glyph. This behaviour doesn't violate any
> specification, but it looks like
> it can be easily improved, as underlying OS framework used under the hood
> does support surrogate pairs.
>
> The proposed change consists of two parts. First part is adjusting the
> code in CoreTextSupport.m
> to handle surrogate pairs while performing char-to-glyph mapping, by
> encoding non-displayable
> surrogate pairs using negative values of the codepoint, similar to how
> non-displayable BMP characters
> are encoded. Second part is fixing the rendering code (in
> CGGlyphImages.m), where wrong type was used
> to pass character values around, so that code for surrogate pairs
> handling, already present there,
> could work.
>
> I didn't include a test for this change, as it would depend on OS-specific
> font fallback mechanism
> and fonts installed, but I can create one that will work on a latest
> version of macOS with default
> fonts, if needed.
>
> Webrev for the fix is available at
> http://cr.openjdk.java.net/~avu/rfe_surrogates/webrev.00/
> (kindly posted by my colleague, having access to cr.openjdk.java.net).
>
> To my knowledge, there's no ticket in OpenJDK issue tracker for the
> proposed enhancement.
> I can submit it via http://bugs.java.com/, if that's an obstacle.
>
> Best regards,
> Dmitry Batrak
>
>


-- 
Dmitry Batrak
Senior Software Developer
JetBrains
http://www.jetbrains.com
The Drive to Develop
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