Re: [ft-devel] State of TrueType interpreter v38 and up?

[Werner LEMBERG]

> Mostly as note to my future self, to summarize those rendering modes
> in DWrite terms, please correct me if I got anything wrong: [...]

All what I know is taken from information from

  
https://msdn.microsoft.com/en-us/library/windows/desktop/dd368118(v=vs.85).aspx

You certainly are aware of that link :-)

> In all cases that offer AA, it could be either cleartype or
> grayscale, it's specified separately from rendering mode.  Could it
> mean that in grayscale mode DWrite NATURAL mode is the same as
> GDI_NATURAL?

The above link says something different.

> I remember that symmetric mode is not supported in freetype yet, so
> we can forget about it.

It's exactly the opposite: FreeType *only* supports symmetric mode
(this is, AA for both the horizontal and vertical axis).  Note that
`symmetric' is not related to subpixel rendering – this can only be
applied to a single axis due to the geometry of current LCD screens.

> So the question is what does freetype support from this list,

It seems that FreeType supports DWRITE_RENDERING_MODE_ALIASED and
DWRITE_RENDERING_MODE_NATURAL_CLASSIC.  All other modes have non-AA
along the vertical axis, which FreeType doesn't implement.

> and how can I switch between different modes?

Since the AA and non-AA rasterizers are two different modules in
FreeType, you can change between these two modes simply by using the
proper FT_LOAD_XXX flag.

> I know that one option is a per-library engine version setting, but
> what does it change in terms of those listed modes

The Windows enumerations combine various aspects of both the hinting
engine and the rasterizer, and those combinations are not available
under FreeType.

> (also is there any reason to never switch it back and forth between
> render operations, performance penalty for example?).

I think this question doesn't apply to FreeType.


    Werner