% Thanks for some changes to:
%+ This is TEXPS.LPRO as modified by Rob Hutchings 1992Apr02
%+ My comments are marked as %+ 
% PostScript prolog for using resident fonts.
%+ Provision is made to change the encoding scheme in special instructions. 
%+ This is the only way to access the 20 characters which are present in  
%+ a standard PostScript font, but not included in the standard encoding. 
% All we do is change the widths so that PostScript positioning 
% matches the assumptions of dvips.

% The calling sequence defining font foo to be resident font Bar is
%+       /foo wd(n-1) ... wd1 wd0 {specials} n atsize /Bar rf
% where each character width wdi is in pixels,
%+ and atsize is the desired font size, after magnification, in pixels.
% The locations of unused characters are specified by codes of the form
% `m [', denoted m consecutive unused characters, interspersed among the
% widths of the n characters that are actually used.
% The total n + (sum of m's) must equal 256.

%
TeXDict begin
%
/rf 
% We copy everything but the FID entry of the resident font
% (just as in section 5.6 of the Red Book second edition).
% We also don't copy UniqueID, even though we want to, because
% this messes up systems that cache the fonts, for some
% PostScript fonts.
{ findfont dup length 1 add dict begin 
        { 1 index /FID ne 2 index /UniqueID ne and
          {def} {pop pop} ifelse } forall
% Now the top entry on the stack is the desired size, which
% we use to construct the matrix to transform the font.
% The way we do this is constrained by our desire to leave
% a hook for extending and/or slanting; the hook also allows
% the font to be reencoded extremely cheaply.
% Extend and slant are coded in positions 0 and 2 of the matrix,
% whose default values are atsize and 0
        [ 1 index 0
% at this point we pick up and obey the special instructions
        6 -1 roll exec  
% which changes `{s} n at [ at 0' to `n at [ AT S' (see SlantFont below)
% and then we will insert the rest of the matrix.  It is imperative that
%   VResolution Resolution div mul
% be used instead of
%   VResolution mul Resolution div
% because the latter gives us floating point roundoff error that
% causes the interpreter to think the font isn't square, and this
% leads to substantially deteriorated character glyphs.
        0 exch 5 -1 roll VResolution Resolution div mul neg 0 0 ]
% The top of stack is now `n [ AT 0 S at*aspect 0 0]';
% we use this matrix to scale the font later.  We store it in Metrics,
% which we'll give a different definition to anyway later.
       /Metrics exch def
% Now we start the dictionary of length n that will eventually be Metrics:
        dict begin
% When the font is used the width in the Metrics dictionary will be 
% multiplied by FontMatrix[0] to give the actual character width. 
% We therefore divide each width by FontMatrix[0] before storing.
% (We assume that FontMatrix has the form [ x 0 0 x 0 0 ].)
% Note that using FontMatrix[0] is safer than assuming milli-em units, 
% and that loading the widths on to the stack rather than using an array 
% allows the following simple coding.
%   We also allow marks on the stack ([) to mean that we don't use
%   that character and thus don't need any Metrics entry for it.
%   This saves lots of VM.
%   A sequence of m marks is represented by `m ['.
        Encoding { exch dup type /integertype ne
          {pop pop 1 sub dup 0 le {pop} {[} ifelse}
             {FontMatrix 0 get div Metrics 0 get div def} ifelse } forall
% Now we put the widths dictionary into the font, after grabbing
% the current definition of Metrics back.
        Metrics /Metrics currentdict end def
% and duplicate /foo so that it can be used both in definefont
% and as the name of the macro, which is created first as a 
% non-executable array so that we can put the new font dictionary 
% itself inside the macro;
        [ 2 index currentdict end definefont 3 -1 roll makefont
% this involves a circumlocution to insert the setfont command.
          /setfont cvx ] 
% Finally the macro is made executable and given the name /foo.
        cvx def } def
%
%   Now here's some oblique hackery... an example of making
%   variants of a resident font look like it is resident.
%+ Since dvips has to repeat the special instructions for each 
%+ incarnation of such a hacked font, there appears to be little virtue in 
%+ the halfway-house of naming the hacked font. I have therefore omitted 
%+ the PostScript names of the modified fonts; 
%+ the defining lines in psfonts could be
%+            rptmro Times-Roman ".167 SlantFont"
%+ My versions of SlantFont and ExtendFont are obeyed in the core of the
%+ main macro, at a point where the stack contains
%+           atsize [ x y
%+ where x and y will become entries 0 and 2 of the transformation matrix.
%   Optionally replace the `slant' by `angle ObliqueSlant';
%   note that the ObliqueSlant of Times-Italic is -15.5 (negative).
%
/ObliqueSlant {   % angle ObliqueSlant slant
    dup sin S cos div neg
    } B

% A slant is multiplied by atsize and added to entry 2 (initially 0)
/SlantFont {4 index mul add} def 

% An extend is simply a multiplier for entry 0 (initially atsize)
/ExtendFont {3 -1 roll mul exch} def

% Since at the point at which the hook is obeyed, the current dictionary
% is that of the new font and writeable, it is trivial to include the
% option of reencoding the font.
/ReEncodeFont {/Encoding exch def} def
end
