stb_truetype.h: Implement support for Embedded Bitmaps.

[kphillisjr]

This is mostly a request be able to support glyphs from TrueType fonts that use Bitmap data.

• [ ] Add Support for Embedded Monochrome bitmap data.
  • [ ] add support for Embedded Bitmap Location Table (EBLC)
  • [ ] Implement Embedded Bitmap Data Table (EBDT)
  • [ ] Optional: Implement Apple's Apple Advanced Typography (AAT) 'bloc' table - is done by copying and expanding the code used to work with the 'EBLC ' table.
  • [ ] Optional: Implement Apple's Apple Advanced Typography (AAT) 'bdat' table - This is an expanded form of the 'EBDT' table. That said, the EBDT and bdat tables are not completely compatible.
• [ ] Add support for Embedded Color Bitmap Data.
  • [ ] Implement Color Bitmap Location Table('CBLC')
  • [ ] Implement Color Bitmap Data Table ('CBDT') support.
  • [ ] Add Support for uncompressed Data - This is in an BGRA format.
  • [ ] Add support for Compressed Data - This is a subset of the PNG Format where specified PNG headers are included.
• [ ] Implement Embedded Bitmap Scaling Table ('EBSC')
• [ ] Add Support for the Standard Bitmap Graphics Table('sbix').
  • [ ] Gracefully Notify user of unsupported formats/tags. This table could define data using pdf data.
  • [ ] Add support for JPEG Encoded Data. This uses the 'jpg ' tag.
  • [ ] Add support for PNG Encoded Data. This uses the 'png ' tag.
  • [ ] Optional: Add support TIFF Data. This uses the 'tiff' tag, and currently stb_image.h does not support this file format.
• [ ] Add Support for Color Pallets - This is not actually a Bitmap format, but instead is a method for using Multiple glyph strikes to color an image.
  • [ ] Implement Color Table(COLR)
  • [ ] Implement Color Palette Table(CPAL)

Test Data:

• Windows includes test data for the EBLC/EBDT fonts.
• FireFox OS Emojis ( https://github.com/mozilla/fxemoji ) have support for the CPAL and COLR Tables.
• The Noto Color Emoji font (see: https://www.google.com/get/noto/ ) is good for testing EBSC, CBLC and CBDT tables. The data is compressed as png format.
• The Emojione font ( see: https://github.com/emojione/emojione/tree/2.2.7 ) has two test files that are of use.
  • emojione-apple.ttf - This is a truetype file using sbix data and png compression.
  • emojione-android.ttf - This truetype file contains CBLC and CBDT tables.

Note: Windows 10 Anniversary Update has been updated to fully support all of these Tables, and can be used to check how each glyph is supposed to be rendered. More information over this topic can be found at: https://msdn.microsoft.com/en-us/library/windows/desktop/mt765165(v=vs.85).aspx. Files.

[nothings]

I definitely have 0 interest in supporting bitmap fonts in stb_truetype.

[pabloko]

Hello, i don't usually refloat old issues, but writing here as it may help someone.

Support for COLR+CPAL fonts is already mostly supported by stb_truetype in its current state. stb_truetype can obtain all the needed glyph layers for the emojis, but does not parse the colr (glyph layers) and cpal (color palettes) tables, but doing it would be fairly trivial as defined in the links.

Luckily, if you implement a shaper like HarfBuzz (wich i stongly recommend), it comes with opentype methods to enumerate COLR layers for given codepoint (see hb_ot_color_glyph_get_layers) and CPAL palettes (see hb_ot_color_palette_get_count and hb_ot_color_palette_get_colors) Displaying: original glyph asociated to the codepoint, Final mix colored with CPAL, and COLR layers associated to the codepoint

As a side note, atlas baker methods on stb_truetype rely on enumerating glyphs by codepoint, but fonts can contain glyphs not associated to a codepoint (ligatures, emoji layers...) so its better to implement your own baking that export glyphs by its id, instead by its associated codepoint, and also thats what HarfBuzz expects in order to build ligatures and replacements, or have the layers available for compositing. Heres a sample of SegoeUIEmoji atlas containing every glyph in the font, if you use bakefont you will notice emoji separated layers aren't there.

Other color fonts can be supported thru HarfBuzz but you would have to provide your own rendering for bitmap/png/svg... wich is outside the scope of stb_truetype, so i fully understand the author's disinterest on color fonts, but given that this library already does the hard stuff, maybe a simple COLR/CPAL parser would be usuful for people that dont want to bring a shaper library but at least match DirectWrite's color capabilities.

@nothings if you're open for a PR i'd gladly add this api