Controlling Layout Direction

The direction of a compound string is stored so that the data structure is equally useful for describing text in left-to-right languages such as English, Spanish, French, and German, or for text in right-to-left languages, such as Hebrew and Arabic. In Motif applications, you can set the layout direction using the XmNlayoutDirection resource from the VendorShell or MenuShell. The Manager and Primitive widget as well as Gadgets, also have an XmNlayoutDirection resource. The default value is inherited from the closest ancestor with the same resource.

In the case of an XmText widget, you must specify the vertical direction as well as the horizontal direction. Setting the layoutDirection to XmRIGHT_TO_LEFT results in the string direction from right to left, but the cursor moves vertically down. If the vertical direction is important and you require top-to-bottom alignment, be sure to specify XmRIGHT_TO_LEFT_TOP_TO_BOTTOM. This setting specifies that the components are laid out from right to left first and then top to bottom, and results in the desired behavior.

The behavior of the XmText and TextField widgets is also influenced by the XmNalignment and XmNlayoutModifier resources of the XmRendition. These resources, in addition to XmNlayoutDirection, control the layout behavior of the Text widget. This behavior is illustrated in Figure 6–2.

The input string used in the figure is:

The XmNlayoutModifier string @ls orientation= setting values for the following figure are shown in the left column.

Figure 6–2 Layout Direction

As the illustration shows, XmNalignment dictates whether the text is flush right or left in conjunction with the layout direction. XmNlayoutModifier breaks the text into segments and arranges them left-to-right or right-to-left, depending on the orientation value. In other words, if the XmNlayoutDirection is XmRIGHT_TO_LEFT, and the XmNAlignment value is XmALIGNMENT_BEGINNING, the string is flush right.

Example 6–1 Creating a Rendition

The following code creates an XmLabel whose XmNlabelString is of the type XmCHARSET_TEXT, using the Rendition whose tag is “ArabicShaped.” The Rendition is created with an XmNlayoutAttrObject of “ar” (corresponding to the locale name for the Arabic locale) and a layout modifier string that specifies for the output buffer a Numerals value of NUMERALS_CONTEXTUAL and a ShapeCharset value of “iso8859–6”.

The locale-specific layout module transforms its input text into an output buffer of physical characters encoded using the 16-bit Unicode codeset. Because an explicit layout locale has been specified, this text is rendered properly independent of the runtime locale setting. In this example, the input is encoded in ISO 8859–6.

int n;
Arg args[10];
Widget w;
XmString labelString;
XmRendition rendition;
XmStringTag renditionTag;
XmRenderTable renderTable;
      /* alef lam baa noon taa - iso8859-6 */
labelString = XmStringGenerate("\307\344\310\346\312\", NULL
			                          XmCHARSET_TEXT, "ArabicShaped");
w = XtVaCreateManagedWidget("a label", xmLabelWidgetClass, parent,
                             XmNlabelString, labelString,
		                          XmNlabelType, XmSTRING,
                             NULL);
n = 0;
XtSetArg(args[n], XmNfontName, "-*-*-medium-r-normal-*-24-*-*-*-*-*-*");
      n++;
XtSetArg(args[n], XmNfontType, XmFONT_IS_XOC); n++;
XtSetArg(args[n], XmNlayoutAttrObject, "ar"); n++;
XtSetArg(args[n], XmNlayoutModifier, 
          "@ls numerals=:contextual, shapecharset=iso8859-6"); n++;
renditionTag = (XmStringTag) "ArabicShaped";
rendition = XmRenditionCreate(w, renditionTag, argcs
s, n);
renderTable = 
    XmRenderTableAddRenditions(NULL, &rendition, 1, XmREPLACE_MERGE);
XtVaSetValues(w, XmNrenderTable, renderTable, NULL);

Example 6–2 Editing a Rendition

The following code creates a TextField widget and a RenderTable with a single Rendition. Both the XmNlayoutAttrObject and XmNlayoutModifier pseudo resources have been left unspecified and therefore default to NULL. This value means that the layout object associated with the Rendition belongs to the default locale, if one exists.

For this example to work properly, the locale must be set to one whose codeset is ISO 8859-6 and whose locale-specific layout module can support the IMPLICIT_BASIC algorithm. The Rendition's LayoutObject's ImplicitAlg value is modified through the Rendition's XmNlayoutModifier pseudo resource.

int n;
Arg args[10];
Widget w;
	XmRendition rendition;
XmStringTag renditionTag;
XmRenderTable renderTable;
w = XmCreateTextField(parent, "text field", args, 0);
n = 0;
	XtSetArg(args[n], XmNfontName, "-*-*-medium-r-normal-*-24-*-*-*-*-*-*-*");
     n++;
	XtSetArg(args[n], XmNfontType, XmFONT_IS_XOC); n++;
renditionTag = (XmStringTag) "ArabicShaped";
rendition = XmRenditionCreate(w, renditionTag, args, n);
renderTable = 
    XmRenderTableAddRenditions(NULL, &rendition, 1, XmREPLACE_MERGE);
XtVaSetValues(w, XmNrenderTable, renderTable, NULL);
	....
n = 0;
XtSetArg(args[n], XmNlayoutModifier, "@ls implicitalg=basic");
     n++;
XmRenditionUpdate(rendition, args, n);