Re: [ft-devel] Stem darkening of new CFF engine

[Werner LEMBERG]

>> Wouldn't it be a good idea to make the amount of darkening user
>> configurable? (Maybe by specifying a number from 0..10 at compile
>> time (0=no darkening ... 10=full darkening))
> 
> This is already on my radar: I'll make the `five-part curve'
> configurable using a CFF driver property.

And now it is implemented and added to the git repository.  From
`ftcffdrv.h':

  @property:
    darkening-parameters

  @description:
    By default, the Adobe CFF engine darkens stems as follows (if the
    `no-stem-darkening' property isn't set):

    {
      stem width <= 0.5px:   darkening amount = 0.4px
      stem width  = 1px:     darkening amount = 0.275px
      stem width  = 1.667px: darkening amount = 0.275px
      stem width >= 2.333px: darkening amount = 0px
    }

    and piecewise linear in-between.  Using the `darkening-parameters'
    property, these four control points can be changed, as the following
    example demonstrates.

    {
      FT_Library  library;
      FT_Int      darken_params[8] = {  500, 300,   // x1, y1
                                       1000, 200,   // x2, y2
                                       1500, 100,   // x3, y3
                                       2000,   0 }; // x4, y4


      FT_Init_FreeType( &library );

      FT_Property_Set( library, "cff",
                                "darkening-parameters", darken_params );
    }

    The x~values give the stem width, and the y~values the darkening
    amount.  All coordinate values must be positive and monotonically
    increasing along the x~axis; the unit is 1000th of pixels.

  @note:
    This property can be used with @FT_Property_Get also.