Re: [ft-devel] [patch] emboldening rework v1

[Behdad Esfahbod]

Humm.  The docs say:

  /*    FT_OUTLINE_EVEN_ODD_FILL ::                                        */
  /*      By default, outlines are filled using the non-zero winding rule. */
  /*      If set to 1, the outline will be filled using the even-odd fill  */
  /*      rule (only works with the smooth rasterizer).                    */

This sounds wrong to me.  I'm fairly sure that FreeType by default does
EVEN_ODD, not WINDING.

  /*                                                                       */
  /*    FT_OUTLINE_REVERSE_FILL ::                                         */
  /*      By default, outside contours of an outline are oriented in       */
  /*      clock-wise direction, as defined in the TrueType specification.  */
  /*      This flag is set if the outline uses the opposite direction      */
  /*      (typically for Type~1 fonts).  This flag is ignored by the scan  */
  /*      converter.                                                       */

This is consistent with EVEN_ODD being the case, not WINDING.

behdad


On 04/10/2012 02:45 PM, Alexei Podtelezhnikov wrote:
> On Tue, Apr 10, 2012 at 11:54 AM, Behdad Esfahbod <address@hidden> wrote:
>> I like the area-based algorithm.  I had to implement outline orientation code
>> recently and I wish I had remembered that algorithm!
>>
>> What I found in testing my implementation was that fonts don't have 
>> consistent
>> contour orientation.  From what I understand:
>>
>>  - TrueType fonts have even-odd fill rule and fill-right orientation,
>>
>>  - Type1 fonts have zero-winding fill rule and fill-left orientation.
>>
>> Now *if* TrueType outlines are really fill-right, then even-odd and
>> zero-winding rules are the same.  But I've came across many fonts where
>> TrueType outlines are even-odd, not fill-right.  I'm guessing that you want 
>> to
>> return ORIENTATION_NONE in those cases.  But finding them is not easy with
>> your algorithm.
> 
> Really, there are *two* questions.
> 1. What is the orientation?
> 2. What is the appropriate fill rule?
> 
> The area based algorithm is more than sufficient to determine the
> orientation. Freetype seem to separate the two concepts as well
> (FT_OUTLINE_EVEN_ODD_FILL is not the same as FT_ORIENTATION_TRUETYPE),
> but then mixes them up again in the function description by referring
> to "fill orientation". I agree that there is a connection that some
> fonts decided to ignore.
> 
> So what is the purpose of this function? Are we interested in the
> orientation of the fill rule?
> 
>> Maybe we don't care really.
> 
> Surprisingly, FT_Oultine_Get_Orientation is not used to render the
> outlines. The smooth rendered flips the negative sing and puts a
> ceiling on the coverage above 1 without thinking twice. I do not even
> know what filling rule that is.
>