Re: [Devel] Postscript hinter and non-square pixels

[David Turner]

Hi Detlef,

  There is nothing in the Postscript hinter that assumes square
  pixel. It's most probably a bug where coordinates and hints have
  their scale factors inversed by accident..

  I've just quickyl hacked "ftstring", which doesn't use the cache,
  to check that, I'll let you know later..

Regards,

- David



Detlef Würkner a écrit :
> 
> Hello!
> 
> I wrote:
> 
> > While playing around with display resolution aspect ratio adaptive code,
> > I found that the Postscript hinter produces really big errors when
> > setting the horizontal resolution to the double value of the vertical
> > resolution with FT_Set_Char_Size() to be displayed correct on an Amiga
> > NTSC screen.
> >
> > The horizontal line of an "A" is e.g. not displayed...
> > With autohinter and without hinter the problem does not appear.
> 
> After the various fixes and enhancements to the PostScript hinter it
> looks better, but the main problem seems to stay: The PostScript hinter
> assumes square pixels. Is this an inherent problem of PostScript hints,
> of the used font or of the hinter?
> 
> To reproduce: I tested with the GhostScript fonts and with Adobe Sans MM
> (from Acrobat Reader IMHO). When specifying non-square pixels with e.g.
> FT_Set_Char_Size(face, 16*64, 0, 72, 36), we tell FreeType that the pixels
> are non-square, 72 dpi horizontal and 36 dpi vertical, e.g. a TV screen
> in non-interlace mode. If displayed on a computer monitor with square
> pixels, an "o" should be about twice as wide than high, on a TV in highres
> non-interlace mode, it should be nearly round.
> 
> When specifying FT_LOAD_NO_HINTING or FT_LOAD_FORCE_AUTOHINT this works
> as expected, but without specifying one of these flags the PostScript
> hinter is used and it always produces a nearly round "o". The TrueType
> hinter works fine. Whether generating monochrome or gray bitmaps makes no
> difference. Oh, and I didn't test without glyphcache, so not
> FT_Set_Char_Size() was used but pix_width and pix_height of
> FTC_Image_Desc had different values.
> 
> Ciao, Detlef
> --
> _ // address@hidden
> \X/  Detlef Wuerkner, Langgoens/Germany
> 
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