[ft-devel] Problem font

[McBride, Martin]

Hi,

 

I wondered if anyone had encountered a problem similar to this, or could recommend a solution.

 

I have a TrueType font with a problem which prevents FreeType from reading its cmap. The font has a format 4 cmap. The final entry has start and end of 0xFFFF, delta of 1, all fine, but the offset is 0x342F, which is far outside of the table. FreeType checks the offset and rejects the cmap as a consequence.

 

The TT spec says “[the final] segment need not contain any valid mappings. It can simply map the single character code 0xFFFF to the missing character glyph, glyph 0.” This is a bit contradictory, but it maybe implies that if the final entry has the range 0xFFFF to 0xFFFF it should be assumed to map onto glyph 0.

 

Unless I have misunderstood the spec, I think the only way to read this font would be by making the assumption above, ie for the last segment, if start and end are 0xFFFF, and delta is 1, force the offset to 0. There is already code to handle offset==0xFFFF in this special case, this change would extend it to handle any invalid offset. I think it would require minor changes in tt_cmap4_validate, tt_cmap4_char_map_linear and tt_cmap4_char_map_binary.

 

Is this a sensible way to proceed, or is it likely to break other things?

 

Regards

 

Martin