Tuesday, September 30, 2008

Flash news: RTL support for DesignGridLayout

Tonight, I have just committed into Subversion the support of right-to-left orientation for DesignGridLayout. as a fix for issue #9.

Implementation was easier than foreseen, except for the test part itself (see below).

First of all, here are 2 screenshots with the same layout, but one uses LTR, the other uses RTL.

DesignGridLayout automatically discovers the orientation to be used for the container it is in charge of laying out, and simply inverts x coordinates if container is RTL-based.

Determining component orientation is based on the Component#getComponentOrientation() method which returns a ComponentOrientation instance. This instance determines the orientation of the text, it is not limited to horizontal LTR (eg English) and RTL (eg Arabic) languages, but also defines languages that are written vertically (all from top to bottom) and which "lines" (should we say "columns"?) are written from right to left (eg Chinese, Japanese) or left to right (eg Mongolian).

However, as far as I know, Swing components LAFs do not support components for vertical languages (I have never seen a vertical JLabel or JTextField), hence for these languages, we have to revert to the "usual" horizontal LTR orientation. For this, DesignGridLayout needs a simple trick to determine text orientation:
ComponentOrientation orientation = parent.getComponentOrientation();
boolean rtl = orientation.isHorizontal() && !orientation.isLeftToRight();

Just using orientation.isLeftToRight() is not sufficient because it would render eg Japanese horizontally from right to left, which I doubt any Japanese person can read (just imagine reading English from right to left!).

As mentioned above, implementing this enhancement was quite easy, but writing test cases for it was much more difficult than I expected.

My original idea for tests was just to set the default Locale to one of English, Arabic, Japanese or Mongolian (in order to cover the four possible situations defined in ComponentOrientation). But it turned out that just creating a new Locale through new Locale("JA") will work only if you have this Locale installed with your JRE, else a new Locale will be instantiated but it will be unusable; in particular, ComponentOrientation.getOrientation(Locale locale) will not return the expected value.

Since my JRE does not include Arabic, Hebrew, Japanese, Chinese and Mongolian, I had to find another way for testing. I chose to directly create a ComponentOrientation instance, but this is not possible since it has no public constructor and it is declared final! The only way to directly use ComponentOrientation is to use one of the 2 provided static instances LEFT_TO_RIGHT and RIGHT_TO_LEFT, which is what I did. But it prevented me from testing the new DesignGridLayout RTL support with vertical orientations.

Hence my call to DesignGridLayout users in Japan or China (for vertical right to left) and Mongolia (for vertical left to right) for testing the latest DesignGridLayout (in subversion trunk) with their respective Locale and send me a screenshot of their results. Thanks in advance!

That'll be all for today.

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