TODO:
=====

CGContext:
 - Have a CGColorSpaceRef attached to the context (currently assumed to be
   sRGB). This will enable things like:
   - Creating a CGBitmapContext in a given color space, then drawing in it
     to convert colors to that color space
   - For people with wide-gamut monitors, we would want to set the appropriate
     color space on the window CGContext.
 - Shadow support is not finished.
 - Image masks are not supported.
 - Need to write a OPGState class that encapsulates the graphics state,
   like CairoGState in -back.
 - Could follow the example of GNUstep back, and factor 
   out Cairo specific code in CGContext to a OPCairoContext subclass.

PostScript/PDF parsing classes are unimplemented.

CGPattern and CGShading unimplemented

Image framework:
 - Need to add TIFF writing
 - The decoders/encoders could be polished:
   - They should read colorspace info, now that Opal can take advantage of it
   - They use the decoding libs to convert to RGBA32, but should pass though
     higher bit-depth images in to Opal and let Opal convert.
 - Could add a plugin which uses ImageMagick for more format support

Build system:
 - Set up so that image plugins, and LCMS classes are only compiled if the 
   libraries are available.

CGFont:
 - Need to refactor to share implementation with OpalText

CGGradient:
 - Should clip the gradient to match Quartz output

Color space and image conversion:
 - Add a placeholder color space conversion class which does non-color managed
   conversions so that LCMS isn't a necessary dependency

OpalText:
 - Still in very early stages. Here is a sketch of what needs to be done:
   - Finish CTFont/CTFontDescriptor/CTFontCollection/CTFontManager with 
     both Fontconfig/Freetype and Windows GDI backends.
     (The basics of CTFontDescriptor are currently working with the
      Fontconfig backend)
   - Implement CTTypesetter, the core part, which requires:
     - Identifying permissible places to break a string with the Unicode
       linebreaking algorithm
     - Run GNU fribidi on the string if needed
     - Deciding what font to use for each range in the string, doing fallback
       where necessary
     - Itemizing the attributed string using 
       -attributesAtIndex:longestEffectiveRange:inRange
       to get the character runs
     - Calling harfbuzz to do OpenType layout, yielding glyph runs and advances
       (+ other simpler layout routines for non-OpenType fonts?)
   - Finish CTFramesetter

Design principles to follow:
============================
- Build on public Cairo APIs as much as possible, use private APIs only if
  there is no appropriate public one or would simplify implementation a lot
- Avoid duplicate representation of the same thing (should not store a copy
  of what Cairo already stores to avoid getting out of sync or too many
  conversions). Choose between Quartz or Cairo representation and convert to
  that and then stick to it.
- Keep performance in mind. This is a low level part of the system that
  should be fast, small and stable so follow K.I.S.S.
- Keep dependencies clean, only #include what you need and put functions
  that depend on the same thing in one file.