15.5 Font protocol

Description of the Font protocol, Revision 5

Minimal support of this protocol consists in the evaluation of the FONT_CHANGED message. Programs that support one of the (GDOS) attributes text angle, text width, kerning, text slope or the setting of the text size in 1/65536 points should also support the XFONT_CHANGED message, which offers additional information.

With the message FONT_SELECT the font-selector can also be called up by the application. During this the currently set attributes can be passsed as well.

If the application also supports the XAcc-2 protocol, then it can also reveal easily the FONT_ACK confirmation message, and search for font selectors in memory even without an environmental variable.

FONT_CHANGED message:
Message from the font-selector to an application that the font and/or character attributes (size, colour and effects) in one or more windows of the application should be changed. If the target application contains in its extended XAcc name the identifier 'XFontAck' then this message has to be replied to with a FONT_ACK message. Otherwise the support for this message is optional.

Negative values in msg[6/7] or zero in msg[4/5] represents no change.

msg[0]  = FONT_CHANGED (0x7a18)
msg[1]  = apID
msg[2]  = 0
msg[3]  = Handle of the affected window, or negative
          value if the font for all windows should be
          changed.
msg[4]  = Font ID, or 0
msg[5]  = Font size in points (>0) or pixels (<0)
          or zero for no change
msg[6]  = Font colour
msg[7]  = Effects:
          Bit 0: Bold
          Bit 1: Light
          Bit 2: Italics
          Bit 3: Underlined
          Bit 4: Outlined
          Bit 5: Shadowed
          Bit 6: Inverse
          Bit 12: 1=Font is monospaced; 0=unknown
          (remaining bits are reserved)

Bit 12 was introduced with Revision 5.

XFONT_CHANGED message:
Convey extended (GDOS) attributes. This message is optional and is sent before the FONT_CHANGED message, i.e. these values may be set only when the FONT_CHANGED message arrives and has the same sender (compare with msg[1]!). This avoids duplicated redraws and/or errors.

The FONT_CHANGED message contains the size, rounded to a point value, i.e. programs that do not support XFONT_CHANGED can use this value.

Font-selectors as a rule only understand this message when one of the conveyed attributes differs from the normal value!

msg[0]   = XFONT_CHANGED (0x7a1b)
msg[1]   = apID
msg[2]   = 0
msg[3/4] = Size in 1/65536 point (fix31)
msg[5]   = Rotation angle in 1/10-degree (0-3599)
msg[6]   = Slope in 1/10-degree (-1800 - 1800)
msg[7]   = Width and kerning:
           Bit 15:    Pair kerning
           Bit 13/14: Track kerning mode (0-3)
           Bit 0-12:  Width in points

           In C:

           typedef struct
           {
               unsigned int  pair  : 1;
               unsigned int  track : 2;
               unsigned int  width : 13;
           } VECTOR_INFO;

FONT_SELECT message:
With this message one can call a font-selector containing in its extended XAcc name the identifier 'XFontAck' that is present in memory. If the application and/or the font-selector does not support the XAcc-2 protocol, then one can still search for the contents of the (AES) environmental variable 'FONTSELECT'. In some cases this variable may contain several names (separated by semicolons), where the names optionally may include the path and file extender, so that under multitasking one can load the font-selector in parallel.

Examples:
```
setenv FONTSELECT=FONT_PAL;FONT_SEL
setenv FONTSELECT=C:\FONTSEL\FONT_SEL.APP;C:\FONTSEL\FONT_PAL.APP
```
But for passive support of the Font protocol, an evaluation of the above-named FONT_CHANGED and XFONT_CHANGED messages suffices.

Negative values in msg[6/7] or a zero in msg[4/5] mean that this parameter is not required, is not to be set, or has not yet been set.
```
msg[0]   = FONT_SELECT (0x7a19)
msg[1]   = apID
msg[2]   = 0
msg[3]   = Handle of the window whose font is to be set,
           or a negative value if the font in all windows
           of the application is to be changed
msg[4]   = Font ID, or 0
msg[5]   = Font size in points (>0) or pixels (<0), or zero
           if the parameter is not required (see above)
msg[6]   = Font colour
msg[7]   = Effects (see above)
```

FONT_ACK message:
Inform the font-selector about whether the FONT_CHANGED message could be evaluated, or the font attributes could be set.

msg[0]   = FONT_ACK (0x7a1a)
msg[1]   = apID
msg[2]   = 0
msg[3]   = TRUE (1):  Message was evaluated
           FALSE (0): Message was ignored
msg[4-7] = 0 (reserved)

Protocols

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