The m_transform_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 character strings.

The m_transform_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:

OutBuf

Any transformed data is stored in OutBuf, converted to ShapeCharset.

Outsize

The number of bytes in OutBuf.

InpToOut

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).

OutToInp

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).

Property

A weighted value that represents peculiar input string transformation properties with different connotations as explained below. If this argument is not a null pointer, 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_transform_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.

The layout object maintains a directional state that keeps track of directional changes, based on the last segment transformed. The directional state is maintained across calls to the layout transformation functions and allows stream data to be processed with the layout 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 OutBuf argument 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 bytes. 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 bytes placed 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 bytes 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 bytes) in OutBuf that identifies the transformed ShapeCharset element of the nth byte in InpBuf. In the case of multibyte encoding, the index points (for each of the bytes of a code element in the InpBuf) to the first byte of the transformed code element in the OutBuf.

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 bytes 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 the byte pointed to by InpBufIndex, that identifies the logical code element of the nth byte in OutBuf. In the case of multibyte encoding, the index will point for each of the bytes of a transformed code element in the OutBuf to the first byte of the code element in the InpBuf.

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_transform_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_transform_layout() function may fail if:

E2BIG

The output buffer is full and the source text is not entirely processed.

EBADF

The layout values are set to a meaningless combination or the layout object is not valid.

EILSEQ

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.

EINVAL

Transformation stopped due to an incomplete composite sequence at the end of the input buffer, or OutSize contains NULL.

ERANGE

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_transform_layout() might be unpredictable or implementation-specific with errno set to EBADF.

See attributes(5) for descriptions of the following attributes:

attributes(5)