[ft] Subpixel rendering for PenTile (and other weird LCD displays)?

[Graeme H]

Hi all,

I've been poking through the Freetype API docs, and I have a couple of
questions about how subpixel rendering is usually done. I'm hoping
someone can either confirm or correct my assumptions, and then point
me in the right direction for what I'm looking at doing.

My guess at the current way for doing subpixel rendering is:

- FT_Render_Glyph(slot, FT_RENDER_MODE_LCD), which gives a greyscale
result 3x wider than needed in slot->bitmap.
- Map resulting bitmap as an RGB (or BGR) buffer, so that individual
buffer array elements turn into sub-pixels when rendered.

So, if that's the normal way to do things, my question is: what are
people doing to do proper subpixel rendering on "weird" LCD displays,
like the PenTile display used in the Nexus One?
(http://blog.javia.org/nexus-one-display-and-subpixel-pattern/)

My guess would be:
- render with FT_RENDER_MODE_LCD.
- filter resulting bitmap so that normal (r,g,b) triplets in the
bitmap are "converted" to:
  big_pixel = (old[0] + old[1]) / 2
  new[0] = big_pixel
  new[1] = old[2]
  new[2] = big_pixel

This seems pretty awkward, but I'm unsure of a better approach after a
naive first look at it. Can anyone on the list suggest a better
approach?

Thanks!