Re: [ft-devel] FT_Slot_LoadFunc load_flags info?

[Werner LEMBERG]

Ian,

you are obviously talking about an FT_GlyphSlotRec structure:

>         // These are obvious
>         slot->metrics.width = myWidth;
>         slot->metrics.height = myHeight;

Depending on the FT_LOAD_NO_SCALE flag, the values are either in
(scaled) 26.6 format or unscaled font units, representing the
dimensions of the *hinted* metrics.

>         slot->metrics.horiBearingX = myMinX; // NEGATIVE ?
>         slot->metrics.horiBearingY = myMaxY;

Yes, these values can be negative too.  Depending on the
FT_LOAD_NO_SCALE flag, the values are either in (scaled) 26.6 format
or unscaled font units, again representing *hinted* metrics.

>         // Advance #1
>         slot->metrics.horiAdvance = 0;
>         ft_synthesize_vertical_metrics(&slot->metrics,
>                                        slot->metrics.vertAdvance);

The horizontal advance is the amount you have to move the cursor to
the right (or down for vertical layouts); this is a *hinted* value.
Depending on the FT_LOAD_NO_SCALE flag, the values are either in
(scaled) 26.6 format or unscaled font units.

>         // Advance #2 (What's the diff?)
>         slot->linearHoriAdvance = 0;
>         slot->linearVertAdvance = 0;

These are *unhinted* values, as needed for device-independent layout.
Depending on the FT_LOAD_LINEAR_DESIGN flag, the values are either in
(scaled) 16.16 format or unscaled font units.

>         // Advance #3 (Unused?)
>         slot->advance.x = 0;
>         slot->advance.y = 0;

This is a shorthand: Depending on FT_LOAD_VERTICAL_LAYOUT, this value
contains either metrics.horiAdvance or metrics.vertAdvance;
additionally, depending on FT_LOAD_IGNORE_TRANSFORM, the
transformation matrix has been applied to it.  I'll try to improve the
documentation which is a bit fuzzy here.

Hopefully, I've got everything right :-)


    Werner