TransAct Technologies ITHERM 280 - Manual (Page 276)

ITherm® 280 Unicode and Fonts iTherm ® 280 Programmer’s Guide
Page 274 Rev C 28-07764
Font Size and Spacing command interactions
There are interactions between some of the following commands and some of the legacy font
selection commands. These interactions need to be considered when developing a application
for this printer.
This printer uses a font rendering engine that relies on the font to provide character size and
spacing information. Unfortunately, legacy applications assume all characters are the same and
that the character size and spacing is fixed. To force the characters rendered by the font
rendering engine to conform to legacy modes of operation, some post generation processing is
performed to reposition the characters into a fixed size cell.
The set minimum character height and width ([ESC] + P and [ESC] + p), the set character
spacing ([ESC] + I, [ESC] + i, [ESC] + J and [ESC] + j), the set minimum line spacing ([ESC] + V
and [ESC] + v), and the legacy font select and spacing commands all interact.
The set minimum character height and width ([ESC] + P and [ESC] + p) commands set
character size but in two different ways. In most systems a character point size refers only to
the line spacing and indirectly to the character height. That is also true. The vertical character
height referenced in these commands refer to the character height including the white space
between lines. The horizontal character width is defined by the font. Normally only the
character height would be specified and the width would be defined by the font and that’s how
these commands work if the Width is defined as zero. If the width is defined as zero this is used
as a flag to the printer to generate characters as defined by the font and use the character width
returned by the font. In effect the vertical point size passed to the font rendering engine is the
same as the horizontal value. The added effect of the width being passed as zero is that any
enforced horizontal spacing is disables. IE the effect of the [ESC] + I, [ESC] + i, [ESC] + J and
[ESC] + j commands are disabled. If the width is not zero, the [ESC] + I, [ESC] + i, [ESC] + J
and [ESC] + j remain in effect and only the resulting character size is changed, the horizontal
spacing is not changed.
The legacy [ESC] ! <n> select the print mode effectively issues a set minimum character height
and width command followed by a set character spacing command without effecting the pseudo
fixed spacing flag.
The pseudo fixed spacing flag is a further complication required for dealing with fonts that are
not truly fixed pitch. In some cases a fixed pitch font will have more that one character size
depending on what the character is used for. This generally only affects Asian fonts where the
ideograms are generally twice as wide as Latin characters. In fixed spacing mode, the printer
will put the rendered character at whatever spacing is requested even if they don’t fit. If the
character is too big, it will overlap the previous and next character. To allow a fixed pitch
operation that deals with small and large fixed pitch character, the printer has a pseudo-fixed
pitch flag that will increase the spacing in multiples of the requested spacing until it fits.
The following table lists the commands and how they interact.
Command Zero Character
width Character
height Cell Width Pseudo Fixed
pitch flag
[ESC] + P,
[ESC] + p Width 0 Same as
Height From
command From Font No effect