- layout transformation for wide character strings
cc [ flag... ] file... –llayout [ library... ] #include <sys/layout.h> int m_wtransform_layout(LayoutObject layout_object, const wchar_t *InpBuf, const size_t ImpSize, const void *OutBuf, size_t *Outsize, size_t *InpToOut, size_t *OutToInp, unsignedchar *Property, size_t *InpBufIndex);
The m_wtransform_layout() function performs layout transformations (reordering, shaping, cell determination) or provides additional information needed for layout transformation (such as the expected size of the transformed layout, the nesting level of different segments in the text and cross-references between the locations of the corresponding elements before and after the layout transformation). Both the input text and output text are wide character strings.
The m_wtransform_layout() function transforms the input text in InpBuf according to the current layout values in layout_object. Any layout value whose value type is LayoutTextDescriptor describes the attributes of the InpBuf and OutBuf arguments. If the attributes are the same for both InpBuf and OutBuf, a null transformation is performed with respect to that specific layout value.
The InpBuf argument specifies the source text to be processed. The InpBuf may not be NULL, unless there is a need to reset the internal state.
The InpSize argument is the number of bytes within InpBuf to be processed by the transformation. Its value will not change after return from the transformation. InpSize set to -1 indicates that the text in InpBuf is delimited by a null code element. If InpSize is not set to -1, it is possible to have some null elements in the input buffer. This might be used, for example, for a “one shot” transformation of several strings, separated by nulls.
Output of this function may be one or more of the following depending on the setting of the arguments:
Any transformed data is stored in OutBuf, converted to ShapeCharset.
The number of wide characters in OutBuf.
A cross-reference from each InpBuf code element to the transformed data. The cross-reference relates to the data in InpBuf starting with the first element that InpBufIndex points to (and not necessarily starting from the beginning of the InpBuf).
A cross-reference to each InpBuf code element from the transformed data. The cross-reference relates to the data in InpBuf starting with the first element that InpBufIndex points to (and not necessarily starting from the beginning of the InpBuf).
A weighted value that represents peculiar input string transformation properties with different connotations as explained below. If this argument is not a nullpointer, it represents an array of values with the same number of elements as the source substring text before the transformation. Each byte will contain relevant “property” information of the corresponding element in InpBuf starting from the element pointed by InpBufIndex. The four rightmost bits of each “property” byte will contain information for bidirectional environments (when ActiveDirectional is True) and they will mean “NestingLevels.” The possible value from 0 to 15 represents the nesting level of the corresponding element in the InpBuf starting from the element pointed by InpBufIndex. If ActiveDirectional is false the content of NestingLevel bits will be ignored. The leftmost bit of each “property” byte will contain a “new cell indicator” for composed character environments, and will have a value of either 1 (for an element in InpBuf that is transformed to the beginning of a new cell) or 0 (for the “zero-length” composing character elements, when these are grouped into the same presentation cell with a non- composing character). Here again, each element of “property” pertains to the elements in the InpBuf starting from the element pointed by InpBufIndex. (Remember that this is not necessarily the beginning of InpBuf). If none of the transformation properties is required, the argument Property can be NULL. The use of “property” can be enhanced in the future to pertain to other possible usage in other environments.
The InpBufIndex argument is an offset value to the location of the transformed text. When m_wtransform_layout() is called, InpBufIndex contains the offset to the element in InpBuf that will be transformed first. (Note that this is not necessarily the first element in InpBuf). At the return from the transformation, InpBufIndex contains the offset to the first element in the InpBuf that has not been transformed. If the entire substring has been transformed successfully, InpBufIndex will be incremented by the amount defined by InpSize.
Each of these output arguments may be null to specify that no output is desired for the specific argument, but at least one of them should be set to a non-null value to perform any significant work.
In addition to the possible outputs above, layout_object maintains a directional state across calls to the transform functions. The directional state is reset to its initial state whenever any of the layout values TypeOfText, Orientation, or ImplicitAlg is modified by means of a call to m_setvalues_layout().
The layout_object argument specifies a LayoutObject returned by the m_create_layout() function.
The OutBufargument contains the transformed data. This argument can be specified as a null pointer to indicate that no transformed data is required.
The encoding of the OutBuf argument depends on the ShapeCharset layout value defined in layout_object. If the ActiveShapeEditing layout value is not set (False), the encoding of OutBuf is guaranteed to be the same as the codeset of the locale associated with the LayoutObject defined by layout_object.
On input, the OutSize argument specifies the size of the output buffer in number of wide characters. The output buffer should be large enough to contain the transformed result; otherwise, only a partial transformation is performed. If the ActiveShapeEditing layout value is set (True) the OutBuf should be allocated to contain at least the InpSize multiplied by ShapeCharsetSize.
On return, the OutSize argument is modified to the actual number of code elements in OutBuf.
When the OutSize argument is specified as zero, the function calculates the size of an output buffer large enough to contain the transformed text, and the result is returned in this field. The content of the buffers specified by InpBuf and OutBuf, and the value of InpBufIndex, remain unchanged. If OutSize = NULL, the EINVAL error condition should be returned.
If the InpToOut argument is not a null pointer, it points to an array of values with the same number of wide characters in InpBuf starting with the one pointed by InpBufIndex and up to the end of the substring in the buffer. On output, the nth value in InpToOut corresponds to the nth byte in InpBuf. This value is the index (in units of wide characters) in OutBufthat identifies the transformed ShapeCharset element of the nth byte in InpBuf.
InpToOut may be specified as NULL if no index array from InpBuf to OutBuf is desired.
If the OutToInp argument is not a null pointer, it points to an array of values with the same number of wide characters as contained in OutBuf. On output, the nth value in OutToInp corresponds to the nth byte in OutBuf. This value is the index in InpBuf, starting with wide character byte pointed to by InpBufIndex, that identifies the logical code element of the nth wide character in OutBuf.
OutToInp may be specified as NULL if no index array from OutBuf to InpBuf is desired.
To perform shaping of a text string without reordering of code elements, the layout_object should be set with input and output layout value TypeOfText set to TEXT_VISUAL and both in and out of Orientation set to the same value.
If successful, the m_wtransform_layout() function returns 0. If unsuccessful, the returned value is -1 and the errno is set to indicate the source of error. When the size of OutBuf is not large enough to contain the entire transformed text, the input text state at the end of the uncompleted transformation is saved internally and the error condition E2BIG is returned in errno.
The m_wtransform_layout() function may fail if:
The output buffer is full and the source text is not entirely processed.
The layout values are set to a meaningless combination or the layout object is not valid.
Transformation stopped due to an input code element that cannot be shaped or is invalid. The InpBufIndex argument is set to indicate the code element causing the error. The suspect code element is either a valid code element but cannot be shaped into the ShapeCharset layout value, or is an invalid code element not defined by the codeset of the locale of layout_object. The mbtowc() and wctomb() functions, when used in the same locale as the LayoutObject, can be used to determine if the code element is valid.
Transformation stopped due to an incomplete composite sequence at the end of the input buffer, or OutSize contains NULL.
More than 15 embedding levels are in source text or InpBuf contain unbalanced directional layout information (push/pop) or an incomplete composite sequence has been detected in the input buffer at the beginning of the string pointed to by InpBufIndex.
An incomplete composite sequence at the end of the input buffer is not always detectable. Sometimes the fact that the sequence is incomplete will only be detected when additional character elements belonging to the composite sequence are found at the beginning of the next input buffer.
A LayoutObject will have a meaningful combination of default layout values. Whoever chooses to change the default layout values is responsible for making sure that the combination of layout values is meaningful. Otherwise, the result of m_wtransform_layout() might be unpredictable or implementation-specific with errno set to EBADF.
Example 1 Shaping and reordering input string into output buffer
The following example illustrated what the different arguments of m_wtransform_layout() look like when a string in InpBuf is shaped and reordered into OutBuf. Upper-case letters in the example represent left-to-right letters while lower-case letters represent right-to-left letters. xyz represents the shapes of cde.
Position: 0123456789 InpBuf: AB cde 12z Position: 0123456789 OutBuf: AB 12 zyxZ Position: 0123456789 OutToInp: 0127865439 Position: 0123456789 Property.NestLevel: 0001111220 Property.CelBdry: 1111111111
The values (encoded in bianry) returned in the Property argument define the directionality of each code element in the source text as defined by the type of algorithm used within the layout_object. Whlie the algorithm may be implementation dependent, the resulting values and levels are defined such as to allow a single method to be used in determining the directionality of the sourece text. The base rules are:
Odd levels are always RTL.
Even levels are always LTR.
The Orientation layout value setting determines the initial level (0 or 1) used.
Within a Property array each increment in the level indicates the corresponding code elements should be presented in the opposite direction. Callers of this function should realize that the Property values for certain code elements is dependent on the context of the given character and the layout values: Orientation and ImplicitAlg. Callers should not assume that a given code element always has the same Property value in all cases.
Example 2 Algorithm to handle nesting
The following is an example of a standard presentation algorithm that handles nesting correctly. The goal of this algorithm is ultimately to return to a zero nest level. Note that more efficient algorithms do exist; the following is provided for clarity rather than for efficiency.
Search for the highest next level in the string.
Reverse all surrounding code elements of the same level. Reduce the nest level of these code elements by 1.
Repeat 1 and 2 until all code elements are of level 0.
The following shows the progression of the example from above:
Position: 0123456789 0123456789 0123456789 InpBuf: AB cde 12Z AB cde 21Z AB 12 edcZ Property.NestLevel: 0001111220 0001111110 0000000000 Property.CellBdry: 1111111111 1111111111 1111111111
See attributes(5) for descriptions of the following attributes: