Tk_ComputeTextLayout,  Tk_FreeTextLayout,  Tk_DrawTextLayout, Tk_Under-
       lineTextLayout, Tk_PointToChar,  Tk_CharBbox,  Tk_DistanceToTextLayout,
       Tk_IntersectTextLayout, Tk_TextLayoutToPostscript - routines to measure
       and display single-font, multi-line, justified text.


       #include <tk.h>

       Tk_ComputeTextLayout(tkfont, string, numChars, wrapLength, justify, flags, widthPtr, heightPtr)


       Tk_DrawTextLayout(display, drawable, gc, layout, x, y, firstChar, lastChar)

       Tk_UnderlineTextLayout(display, drawable, gc, layout, x, y, underline)

       Tk_PointToChar(layout, x, y)

       Tk_CharBbox(layout, index, xPtr, yPtr, widthPtr, heightPtr)

       Tk_DistanceToTextLayout(layout, x, y)

       Tk_IntersectTextLayout(layout, x, y, width, height)

       Tk_TextLayoutToPostscript(interp, layout)


       Tk_Font         tkfont         (in)      Font to use when  constructing
                                                and  displaying a text layout.
                                                The tkfont must  remain  valid
                                                for  the  lifetime of the text
                                                layout.    Must   have    been
                                                returned by a previous call to

       const char      *string        (in)      Potentially multi-line  string
                                                whose  dimensions  are  to  be
                                                computed  and  stored  in  the
                                                text  layout.  The string must
                                                remain valid for the  lifetime
                                                of the text layout.

       int             numChars       (in)      The  number  of  characters to
                                                consider from string.  If num-
                                                Chars  is  less  than  0, then
                                                assumes string is null  termi- |
                                                nated and uses Tcl_NumUtfChars |
                                                to  determine  the  length  of |

       int             wrapLength     (in)      Longest    permissible    line
                                                length, in pixels.   Lines  in
                                                string  will  automatically be
                                                broken at word boundaries  and
                                                wrapped  when  they reach this
                                                length.  If wrapLength is  too
                                                small  for even a single char-
                                                acter to fit  on  a  line,  it
                                                will  be expanded to allow one
                                                character to fit on each line.
                                                If  wrapLength  is <= 0, there
                                                is  no   automatic   wrapping;
                                                lines will get as long as they
                                                need to be and only wrap if  a
                                                newline/return   character  is

       Tk_Justify      justify        (in)      How to justify the lines in  a
                                                multi-line  text layout.  Pos-
                                                sible   values   are   TK_JUS-
                                                TIFY_LEFT,  TK_JUSTIFY_CENTER,
                                                or TK_JUSTIFY_RIGHT.   If  the
                                                text  layout  only  occupies a
                                                single line, then  justify  is

       int             flags          (in)      Various    flag   bits   OR-ed
                                                together.       TK_IGNORE_TABS
                                                means   that   tab  characters
                                                should not be expanded to  the
                                                next tab stop.  TK_IGNORE_NEW-
                                                LINES    means    that    new-
                                                line/return  characters should
                                                not cause a  line  break.   If
                                                either     tabs     or    new-
                                                lines/returns   are   ignored,
                                                then  they  will be treated as
                                                regular characters, being mea-
                                                sured and displayed in a plat-
                                                form-dependent    manner    as
                                                described  in Tk_MeasureChars,
                                                and will not have any  special

       int             *widthPtr      (out)     If   non-NULL,   filled   with
                                                either the width,  in  pixels,
                                                of the widest line in the text
                                                layout, or the width, in  pix-
                                                els,  of  the bounding box for
                                                the  character  specified   by

       int             *heightPtr     (out)     If   non-NULL,   filled   with
                                                either the  total  height,  in
                                                pixels,  of  all  the lines in
                                                the  text   layout,   or   the
                                                height,   in  pixels,  of  the
                                                bounding box for the character
                                                specified by index.

       Tk_TextLayout   layout         (in)      A  token  that  represents the
                                                cached   layout    information
                                                about  the single-font, multi-
                                                line, justified piece of text.
                                                This   token  is  returned  by

       Display         *display       (in)      Display on which to draw.

       Drawable        drawable       (in)      Window or pixmap in  which  to

       GC              gc             (in)      Graphics  context  to  use for
                                                drawing text layout.  The font
                                                selected  in this GC must cor-
                                                respond  to  the  tkfont  used
                                                when   constructing  the  text

       int             x, y           (in)      Point, in pixels, at which  to
                                                place the upper-left hand cor-
                                                ner of the text layout when it
                                                is being drawn, or the coordi-
                                                nates of a point (with respect
                                                to  the upper-left hand corner
                                                of the text layout)  to  check
                                                against the text layout.

       int             firstChar      (in)      The index of the first charac-
                                                ter to  draw  from  the  given
                                                text  layout.   The  number  0
                                                means to draw from the  begin-

       int             lastChar       (in)      The  index of the last charac-
                                                ter up to which to draw.   The
                                                character     specified     by
                                                lastChar itself  will  not  be
                                                drawn.   A  number less than 0
                                                means to draw  all  characters
                                                in the text layout.

       int             underline      (in)      Index  of the single character
                                                to underline in the text  lay-
                                                out,  or  a number less than 0
                                                for no underline.

       int             index          (in)      The  index  of  the  character
                                                whose bounding box is desired.
                                                The bounding box  is  computed
                                                with respect to the upper-left
                                                hand corner of the  text  lay-

       int             *xPtr, *yPtr   (out)     Filled   with  the  upper-left
                                                hand corner, in pixels, of the
                                                bounding box for the character
                                                specified by index.  Either or
                                                both  xPtr  and  yPtr  may  be
                                                NULL, in which case the corre-
                                                sponding  value  is not calcu-

       int             width, height  (in)      Specifies   the   width    and
                                                height,   in  pixels,  of  the
                                                rectangular  area  to  compare
                                                for  intersection  against the
                                                text layout.

       Tcl_Interp      *interp        (out)     Postscript  code   that   will
                                                print   the   text  layout  is
                                                appended to interp->result.


       These routines are for measuring  and  displaying  single-font,  multi-
       line,  justified text.  To measure and display simple single-font, sin-
       gle-line strings,  refer  to  the  documentation  for  Tk_MeasureChars.
       There  is  no  programming  interface  in  the core of Tk that supports
       multi-font, multi-line text; support for that behavior must be built on
       top  of  simpler layers.  Note that unlike the lower level text display |
       routines, the functions described here all  operate  on  character-ori- |
       ented  lengths  and  indices rather than byte-oriented values.  See the |
       description of Tcl_UtfAtIndex for more details  on  converting  between |
       character and byte offsets.

       The  routines described here are built on top of the programming inter-
       face described in the Tk_MeasureChars  documentation.   Tab  characters
       and  newline/return characters may be treated specially by these proce-
       dures, but all other characters are passed through to the lower  level.

       Tk_ComputeTextLayout  computes the layout information needed to display
       a single-font, multi-line, justified  string  of  text  and  returns  a
       Tk_TextLayout token that holds this information.  This token is used in
       subsequent calls to procedures such as Tk_DrawTextLayout,  Tk_Distance-
       ToTextLayout,  and  Tk_FreeTextLayout.  The string and tkfont used when
       computing the layout must remain valid for the lifetime of this  token.

       Tk_FreeTextLayout is called to release the storage associated with lay-
       out when it is no longer needed.  A layout should not be  used  in  any
       other text layout procedures once it has been released.

       Tk_DrawTextLayout  uses  the information in layout to display a single-
       font, multi-line, justified string of text at the specified location.

       Tk_UnderlineTextLayout uses the information in  layout  to  display  an
       underline  below an individual character.  This procedure does not draw
       the text, just the underline.  To produce natively underlined text,  an
       underlined  font  should  be  constructed  and  used.   All characters,
       including tabs, newline/return characters, and spaces at  the  ends  of
       lines,  can  be  underlined  using this method.  However, the underline
       will never be drawn outside of the computed width of layout; the under-
       line  will  stop  at  the edge for any character that would extend par-
       tially outside of layout, and the underline will not be visible at  all
       for  any character that would be located completely outside of the lay-

       Tk_PointToChar uses the information in layout to determine the  charac-
       ter closest to the given point.  The point is specified with respect to
       the upper-left hand corner of the layout, which  is  considered  to  be
       located at (0, 0).  Any point whose y-value is less that 0 will be con-
       sidered closest to the first character in the text  layout;  any  point
       whose  y-value  is  greater  than the height of the text layout will be
       considered closest to the last character in the text layout.  Any point
       whose  x-value  is  less than 0 will be considered closest to the first
       character on that line; any point whose x-value  is  greater  than  the
       width of the text layout will be considered closest to the last charac-
       ter on that line.  The return value is the index of the character  that
       was closest to the point.  Given a layout with no characters, the value
       0 will always be  returned,  referring  to  a  hypothetical  zero-width
       placeholder character.

       Tk_CharBbox  uses  the information in layout to return the bounding box
       for the character specified by index.  The width of the bounding box is
       the  advance  width  of the character, and does not include any left or
       right bearing.  Any character that extends partially outside of  layout
       is considered to be truncated at the edge.  Any character that would be
       located completely outside of layout is considered to be zero-width and
       pegged  against  the  edge.  The height of the bounding box is the line
       height for this font, extending from the top of the ascent to the  bot-
       tom  of  the descent; information about the actual height of individual
       letters is not available.  For measurement purposes, a layout that con-
       tains no characters is considered to contain a single zero-width place-
       holder character at index 0.  If index was not a valid character index,
       the  return  value is 0 and *xPtr, *yPtr, *widthPtr, and *heightPtr are
       unmodified.  Otherwise, if index did specify a valid, the return  value
       is  non-zero,  and  *xPtr,  *yPtr, *widthPtr, and *heightPtr are filled
       with the bounding box information for the character.  If any  of  xPtr,
       yPtr,  widthPtr,  or heightPtr are NULL, the corresponding value is not
       calculated or stored.

       Tk_DistanceToTextLayout computes the shortest distance in  pixels  from
       the  given  point  (x,  y) to the characters in layout.  Newline/return
       characters and non-displaying space characters that occur at the end of
       individual  lines in the text layout are ignored for hit detection pur-
       poses, but tab characters are not.  The return value is 0 if the  point
       actually  hits the layout.  If the point didn't hit the layout then the
       return value is the distance in pixels from the point to the layout.

       Tk_IntersectTextLayout  determines  whether  a  layout  lies   entirely
       inside,   entirely  outside,  or  overlaps  a  given  rectangle.   New-
       line/return characters and non-displaying space characters  that  occur
       at  the end of individual lines in the layout are ignored for intersec-
       tion calculations.  The return value is -1 if the  layout  is  entirely
       outside  of  the  rectangle,  0 if it overlaps, and 1 if it is entirely
       inside of the rectangle.

       Tk_TextLayoutToPostscript outputs code consisting of a Postscript array
       of  strings  that  represent the individual lines in layout.  It is the
       responsibility of the caller to take the Postscript  array  of  strings
       and add some Postscript function operate on the array to render each of
       the lines.  The code that represents the Postscript array of strings is
       appended to interp->result.


       When measuring a text layout, space characters that occur at the end of
       a line are ignored.  The space characters still exist and the insertion
       point  can  be  positioned  amongst them, but their additional width is
       ignored when justifying lines or returning the total width  of  a  text
       layout.  All end-of-line space characters are considered to be attached
       to the right edge of the line; this behavior is logical for left-justi-
       fied text and reasonable for center-justified text, but not very useful
       when editing right-justified  text.   Spaces  are  considered  variable
       width  characters;  the  first  space that extends past the edge of the
       text layout is clipped to the edge, and any subsequent  spaces  on  the
       line  are  considered  zero  width  and pegged against the edge.  Space
       characters that occur in the middle of a line  of  text  are  not  sup-
       pressed and occupy their normal space width.

       Tab  characters are not ignored for measurement calculations.  If wrap-
       ping is turned on and there are enough tabs on a  line,  the  next  tab
       will  wrap  to the beginning of the next line.  There are some possible
       strange interactions between tabs and justification; tab positions  are
       calculated  and the line length computed in a left-justified world, and
       then the whole resulting line is shifted so it is  centered  or  right-
       justified, causing the tab columns not to align any more.

       When wrapping is turned on, lines may wrap at word breaks (space or tab
       characters) or newline/returns.  A dash or hyphen character in the mid-
       dle  of  a  word  is not considered a word break.  Tk_ComputeTextLayout
       always attempts to place at least one word on each line.  If it  cannot
       because  the  wrapLength  is  too small, the word will be broken and as
       much as fits placed on the line and the rest on subsequent line(s).  If
       wrapLength  is  so small that not even one character can fit on a given
       line, the wrapLength is ignored for that line and one character will be
       placed  on  the  line  anyhow.   When wrapping is turned off, only new-
       line/return characters may cause a line break.

       When a text layout has been created using an  underlined  tkfont,  then
       any  space  characters  that occur at the end of individual lines, new-
       lines/returns, and tabs will not be displayed underlined when  Tk_Draw-
       TextLayout is called, because those characters are never actually drawn
       - they are merely placeholders maintained in the layout.



Tk                                    8.1              Tk_ComputeTextLayout(3)

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