@startuml v5_split_downconvert

title
How to split and down-convert a DesignSpace version 5
<size:14>so that existing tools can work with it
end title


start

#lightgrey:DesignSpace 5.0
- with STAT data
- optional instance names
- with discrete axes
- with multiple VFs]

note left
  - STAT data means that compilers will need
  to write that data to the ouput TTFs
  - optional instance names means that
  compilers will need to generate any missing
  names using the STAT data
  - discrete axes mean that not all sources
  are compatible for interpolation
  - multiple VFs means that compilers will
  need to output several TTFs for one DS
end note

split
split again

:""splitInterpolating()"";

note left
  - Create one DS document per interpolating
  sub-space, for example: with a discrete
  axis for Upright vs Italics, create 2
  DesignSpaces, one for the Uprights, and
  one for the Italics.
  - Expand all missing instance names using
  the STAT data.
  - Drop all the STAT data because as we start
  taking out discrete axes, the sub-documents
  lose STAT data anyway (only the full
  document at the start of the process should
  be used to generate the STAT table)
end note

split

  #lightgrey:DesignSpace 5.0
  - (no STAT data)
  - (explicit instance names)
  - (at discrete location #1)
  - with multiple VFs]

  note left
    All sources in this sub-space are
    (supposed to be) compatible for
    interpolation
  end note

split again

  #lightgrey:DesignSpace 5.0
  - (no STAT data)
  - (explicit instance names)
  - (at discrete location #2)
  - with multiple VFs]
  detach

split again

  #lightgrey:etc
  ...]
  detach

end split

:check compatibility;
:build compatible master TTFs with cu2qu;

:""splitVariableFonts()"";

note left
  Create one DS document per variable font,
  for example: the above document may
  describe a weight and width space, out of
  which we'll build 3 variable fonts:
  full weight + width, weight only, width only.
end note

split

  #lightgrey:DesignSpace 5.0
  - (no STAT data)
  - (explicit instance names)
  - (at discrete location #1)
  - (describing just VF #1)]

  note left
    This document looks very much
    like version 4.1, you can just
    change the version number at
    the top and feed it to a tool
    that doesn't know about v5;
    see ""convert5to4()"".
  end note

split again

  #lightgrey:DesignSpace 5.0
  - (no STAT data)
  - (explicit instance names)
  - (at discrete location #1)
  - (describing just VF #2)]
  detach

split again

  #lightgrey:etc
  ...]
  detach

end split

:""varLib.build()"";

#lightgrey:Variable font TTF
No STAT data]

end split

:""buildVFStatTable()"";

note left
Apply STAT data using the full document
from the start of the process + filtering
entries based on this VF's location
end note

#lightgrey:Variable font TTF
With STAT data]

end

@enduml