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How to center text on page in PostScript for CID-Keyed fonts converted from ttf related to Indian Languages?

This post is sequel to Conversion from ttf to type 2 CID font (type 42 base font)

How to write a postscript program that centers a text generated from character set of CID-Keyed fonts on a page?

Note: CID-Keyed fonts are Type 0 Composite fonts which have been converted from truetype fonts applicable to Indian Languages. Without this conversion, no postscript program can access truetype fonts.

Thanks in advance.

Added the following Demonstration Postscript Program.

The CID-keyed font NotoSansTamil-Regular.t42 has been converted from Google's Tamil ttf font. Refer Post Conversion from ttf to type 2 CID font (type 42 base font) for conversion.

On Windows platform make sure that NotoSansTamil-Regular.t42 file is available in folder D:\cidfonts (or any other drive of convenience).

On Linux platform, make sure that NotoSansTamil-Regular.t42 file is available in folder ~/cidfonts.

Write the following Postscript program D:\cidfonts\center.ps on Windows platform or ~/cidfonts/center.pson Linux platform as given below:

%!PS-Adobe-3.0
/CTXT {dup stringwidth pop 3 -1 roll 2 copy lt {sub neg 2 div 4 -1 roll add 3 -1 roll} {pop pop 3 1 roll} ifelse  moveto show} bind def     % Center text. usage: X Y Width <Hex String> CTX. Example-1: 36 300 500 <Hex String> CTXT and Example-2: 36 300 500 (String) CTXT
/myNoTo {/NotoSansTamil-Regular findfont exch scalefont setfont} bind def   % usage: 15 myNoTo

13 myNoTo
% தமிழ் தங்களை வரவேற்கிறது!
0 500 594 <0155017201aa019801a500030163018801a5017f01b101aa018801c20003016901b101cb00aa> CTXT

% Tamil Welcomes You!
0 450 594 <0019001d002a005e00030019004e00120030002200030024001f002f0024005b0012002a0020007a00aa> CTXT
showpage

Issue the following Ghostscript command to execute the postscript program center.ps.

  • gswin64c.exe "D:\cidfonts\NotoSansTamil-Regular.t42" "D:\cidfonts\center.ps (on Windows Platform).
  • gs ~/cidfonts/NotoSansTamil-Regular.t42 ~/cidfonts/center.ps (on Linux Platform).

This will display two strings தமிழ் தங்களை வரவேற்கிறது! and Tamil Welcomes You! respectively centered in two subsequent rows of the page.

Solution

  • Centering should work roughly the same regardless of the font's type.

    The simple method is to use the stringwidth operator which returns the x displacement and y displacement for the string according to the current font. But this will only give you one axis for centering. A left-to-right or right-to-left font will return 0 for the y displacement.

    /bounds gsave clippath [ pathbbox ] grestore def
/min_x bounds 0 get def
/max_x bounds 2 get def
/span_x max_x min_x sub def

%center along x axis, requires currentpoint to be set to determine y coord
/cshow {
  dup stringwidth pop span_x exch sub 2 div min_x add
  currentpoint exch pop moveto
  show
} def

    If you need to center a string along both axes, you'll need to get a bounding box for the string using (string) false charpath flattenpath pathbbox.