1. cshow
Show text with procedure invoked for each character (Level 2).
1.4. Description
cshow invokes proc once for each operation of the font mapping algorithm. The value of currentfont during the execution of proc is the base font that the algorithm ultimately selects.
When proc is invoked, the stack contains three values:
1. The selected character’s code (an integer)
2. The x component of the width vector for the character in user coordinate system
3. The y component of the width vector for the character in user coordinate system
cshow does not paint the character and does not change the current point, although proc may do so. When proc completes execution, the value of currentfont is restored.
cshow can be used to provide careful positioning of individual characters while taking advantage of the composite font mapping machinery of the interpreter. cshow is intended primarily for use with composite fonts. However, it can also be used with a base font. The mapping algorithm for a base font simply selects consecutive characters from the string.
1.5. Parameters
proc (procedure)
: Procedure to execute for each character; receives character code, wx, and wy on stack
string (string)
: The text to process
1.6. Procedure Arguments
When proc is called, the stack contains:
charCode wx wyWhere:
- charCode - Integer character code selected by font mapping
- wx - X component of character width in user space
- wy - Y component of character width in user space
1.7. Examples
1.7.1. Character-by-Character Positioning
/customPlace { % charCode wx wy customPlace -
% Move to next position and paint character
2 copy rmoveto % Move by width vector
pop pop % Remove wx, wy
% Get character and show it
1 string dup 0 4 -1 roll put
currentfont /Encoding get exch get
glyphshow
} def
/Helvetica findfont 12 scalefont setfont
100 700 moveto
/customPlace load (Custom) cshow1.7.2. Composite Font Processing
% Process each character from composite font
/processComposite { % charCode wx wy processComposite -
% charCode is the final mapped code
% currentfont is the selected base font
currentfont /FontName get == % Print which font
3 1 roll % charCode at top
% Paint character at current position
1 string dup 0 4 -1 roll put
dup show
% Advance by width
exch 0 rmoveto pop
} def
/CompositeFont findfont 12 scalefont setfont
100 700 moveto
/processComposite load (Text) cshow1.7.3. Character Analysis
% Collect character information
/analyzeChars { % charCode wx wy analyzeChars -
% Store information about each character
3 copy
4 dict begin
/wy exch def
/wx exch def
/code exch def
/font currentfont /FontName get def
% Print analysis
(Char: ) print code =string cvs print
( Font: ) print font =string cvs print
( Width: ) print wx = wy =
end
% Advance and paint
rmoveto
} def
100 700 moveto
/analyzeChars load (ABC) cshow1.7.4. Vertical Text Layout
% Use wy for vertical advancement
/verticalShow { % charCode wx wy verticalShow -
exch pop % Use only wy
0 exch neg rmoveto % Move down by height
% Paint character
1 string dup 0 4 -1 roll put show
} def
/Helvetica findfont 12 scalefont setfont
100 700 moveto
/verticalShow load (VERTICAL) cshow1.8. Errors
invalidfont : Current font is not valid
invalidaccess : Font or string has restricted access
nocurrentpoint : Current point is not defined
rangecheck : Character mapping out of bounds
stackunderflow : Fewer than two operands on stack
typecheck
: proc is not executable or string is not a string
1.9. Font Mapping with Composite Fonts
For composite fonts, cshow invokes the font mapping algorithm:
-
FMapType determines how to map string bytes to font selection
-
Selected base font becomes current during
procexecution -
Character code is the final mapped code in the base font
-
Width vector is from the selected base font
Example font mapping flow:
String byte → FMapType algorithm → (font#, charCode)
→ Select base font
→ Get character width
→ Call proc with (charCode, wx, wy)1.10. Advanced Applications
1.10.1. Glyph Substitution
% Replace specific characters with alternates
/substituteGlyph { % charCode wx wy substituteGlyph -
3 1 roll % wx wy charCode
% Check for substitution
dup 65 eq { % Replace 'A' with special glyph
pop
/A.swash % Substitute glyph name
} {
% Convert code to glyph name
currentfont /Encoding get exch get
} ifelse
% Show glyph
glyphshow
% Advance by width
rmoveto
} def
100 700 moveto
/substituteGlyph load (SWASH CAPS) cshow1.10.2. Multi-Color Text
% Alternate colors for each character
/colorIndex 0 def
/rainbowProc { % charCode wx wy rainbowProc -
3 1 roll % charCode at top for later
% Set color based on index
colorIndex 6 mod
dup 0 eq { 1 0 0 setrgbcolor } if % Red
dup 1 eq { 1 0.5 0 setrgbcolor } if % Orange
dup 2 eq { 1 1 0 setrgbcolor } if % Yellow
dup 3 eq { 0 1 0 setrgbcolor } if % Green
dup 4 eq { 0 0 1 setrgbcolor } if % Blue
dup 5 eq { 0.5 0 1 setrgbcolor } if % Purple
pop
/colorIndex colorIndex 1 add def
% Paint character
exch 0 rmoveto pop
1 string dup 0 4 -1 roll put show
} def
100 700 moveto
/rainbowProc load (RAINBOW TEXT) cshow1.11. Composite Font Example
% Define composite font (simplified)
/MyComposite 10 dict begin
/FontType 0 def
/FMapType 2 def
/FontMatrix [1 0 0 1 0 0] def
/FDepVector [
/Helvetica findfont
/Symbol findfont
] def
/Encoding [0 1] def % Simple 2-font encoding
currentdict
end /MyComposite exch definefont pop
% Use with cshow
/MyComposite findfont 12 scalefont setfont
/showWithFont { % charCode wx wy showWithFont -
currentfont /FontName get == % Print selected font
rmoveto pop
1 string dup 0 4 -1 roll put show
} def
100 700 moveto
/showWithFont load (Mixed fonts) cshow1.13. See Also
-
show- Basic text painting -
ashow- Show with uniform spacing -
kshow- Show with kerning procedure -
currentfont- Get current font -
glyphshow- Show glyph by name -
rootfont- Get root composite font