Re: [ft] Dark pixels at the edge of rendered glyphs.

[R0b0t1]

On Thu, Apr 13, 2017 at 2:26 AM, Werner LEMBERG <address@hidden> wrote:
>
>> Rendered glyphs passed to OpenGL as a texture and then "properly"
>> blended with a background color show dark pixels on the edges.
>> [...]
>
> I'm no expert w.r.t. blending, but I think you get these artifacts if
> you don't do the blending in linear color space.  In other words, you
> have to undo gamma, apply the blending, then apply gamma again.
>
> Look, for example, at this page
>
>   http://ninedegreesbelow.com/photography/linear-gamma-blur-normal-blend.html
>

I really appreciate the link. That helps me narrow it down to the
blending mode. Unfortunately I'm not able to find any useful
information to follow that up with. I realize that it is almost
certainly not a FreeType2 issue at this point, but you seem to have a
better idea of where to go next than I do.

I tried referring to https://en.wikipedia.org/wiki/Blend_modes to
determine what the most commonly suggested OpenGL blending mode,
`GL_ONE_MINUS_SRC_ALPHA`, corresponds to, but was unable to figure it
out. I'm also not really sure what to call the blending operation in
what you gave me so that I can search for it.

A page 
(http://web.archive.org/web/20081207015323/http://www.processingblogs.org/2007/03/31/mini-tutorial-additive-blending/)
suggested using GL_ONE but I did not see any change in my results when
using it. Better documentation references extensions which allow more
customization in the blending parameters but all of the suggested
options replicate what I am already experiencing
(https://www.khronos.org/opengl/wiki/Blending#Colors).

Some experimentation leads me to wonder if my desired result can even
be obtained because I see the same behavior in commercial software. In
the case of PowerShell it seems like the colors were selected to make
the blending artifacts, if they are that, less noticeable, as the
developers were unable to remove them.

Cheers,
     R0b0t1.