Maxim

(ניתן לראות פוסט זה עם תרגום לעברית)

Two weeks ago I've being asked to add a support for Hebrew texts in our last Silverlight project - "Com-Unit", this application is used by sport commentators and provides graphical presentation for real-time basketball statistics. Also displays some sportive "Trivia" about teams and players, this "Trivia" is written in Hebrew. I knew that it will lead to many problems, because MS didn't add (yet) RTL support in any version of Silverlight.

In "Ice Age of Silverlight 1.1" (couple months before Justin had published his library) I developed very simple "TextBlockWrapper" with primitive algorithm for Hebrew texts conversion and forgotten about it. I tried to implement this library and discovered that it's primitive algorithm can't be used with mixed texts (especially from sportive area).

It managed with texts like this:

But more complicated texts are messed:

I didn't have time and passion to deal with fixing of my algorithm, but remembered that somewhere are good men that developed Silverlight Library with RTL support for Hebrew and Arabic (Tamir, Justin, and others). This is quit good open source project with few bugs that can be fixed.

I found that "TextBlock" has some minor bugs:

Wrong display of properties in MS Blend 2.0:

(All properties that tagged [TypeConverter(typeof(EnumValueConverter<TextWrapping>))] can't be displayed properly)

All texts are wrapped badly (paragraphs are spliced in wrong places):
 
(As you can see there is a lot of empty space on left side) 

MS Blend crashed some times after changes in property grid of control:

(This one appeared when I tried to reset "Text" property)

In general this is good library, can be fixed and extended. I decided to mix good things from both projects and to fix small parts in "TextBlock".

My "TextBlockWrapper" is using original Silverlight "TextBlock" to measure strings for better text wrapping, so I made some changes:

(No text is sliced in right places and wrapped much better)

I added small class "StringFormatter" with 2 functions for paragraph splitting:

This one is measuring size of text, using "TextBlock" than expends it self by text:

public static Size MeasureString(string text, FontFamily fontFamily, double fontSize)
{
    // very important: use "System.Windows.Controls.TextBlock" from Silverlight
    // to avoid recursive call in "BiDiControls.TextBlock"
    var textBlock = new Controls.TextBlock
                        {
                            FontFamily = fontFamily,
                            FontSize = fontSize,
                            Text = text
                        };
    return new Size(textBlock.ActualWidth, textBlock.ActualHeight);
}

(Note: the function has some disadvantage - each call creates new instance of "TextBlock" control, any suggestion for improvement will be accepted with joy)

This one is splitting text into paragraphs (helps "TextBlock" to wrap RTL text properly):

public static string SplitParagraphs(string text, double targetWidth, FontFamily targetFontFamily, double targetFontSize)
{
    if (string.IsNullOrEmpty(text) || text.Length < 2) return text;
    Size s = MeasureString(text, targetFontFamily, targetFontSize);
    if (s.Width < targetWidth) return text;
    int indents = (int) Math.Round(s.Width/targetWidth);
    int length = text.Length/indents;
    for (int i = 0; i < indents; i++)
    {
        int index = text.IndexOf(" ", length*(i + 1) - 1);
        if (index < 0) continue;
        text = text.Insert(index, "\r");
    }
    return text;
}

(Note: the function has some disadvantage - requires exact width of control, any suggestion for improvement will be accepted with joy)

The "BidiControls" uses "NBidi" algorithm (developed by good man: Itai Bar-Haim), now I use it in my small library.

Now my "TextBlockWrapper" displays mixed text in right way:

("NBidi" converts text with brackets, parenthesis and other stuff much better then mine - I'm lazy :), but you can see minor defect on right side of "TextBlock" - each sentence is padded with small space character, I don't know if it comes from "NBidi" or wrapped "TextBlock" has this problem, same problem we can see in "BidiControls" too)

"TextBlockWrapper":

Some properties are wrapping original properties of internal "TextBlock" and some are new:

(bool) AutoDetectTextFlowDirection: if = [true], the text flow will be automatically detected by unicode characters.

(double) LineBorderIndent: (temp. prop.) used for paragraphs' padding.

(TextAlignmentExtended) TextAlign: extended property for text alignment, now supports "Left", "Right", "Center" and "ByTextFlowDirection" (then text is automatically aligned according to RTL/LTR flow direction); "Justify" will be added later.

(TextFlowDirection) TextFlowDirection: "RightToLeft" or "LeftToRight".

(bool) UseNBidiAlgorithm: if = [true], the text will converted by "NBidi" algorithm, otherwise by mine (can be used with simple texts, works faster then "NBidi").

Links to pages with binaries, source code, license, documentation and other stuff:

"RtlSupport" project page on Codeplex.com

"BidiControls" project page on Codeplex.com (patch is available here).

Source code can be downloaded also from here.

PS: I'm not responsible for any damage that may be caused from reading this post or by using binaries, sources or other stuff that is related to this post or my blog. Fill free to use/extend/improve/publish my library with reference to my blog or to my email. Blah, blah, blah...