add ensureDecompiled method to decompile all the tables irrespective of lazy attribute #2551
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previously cmap was completely ignoring lazy attribute, always loading lazily
to 'expand' all the lazy glyphs
can be useful to traverse a tree of otTables
to unlazify a whole tree of otTables, recursively
Make lazy=False actually do what it says, 'load everything eagerly'. It feels weird that one has to, not only say, open with lazy=False, but also have to load each tables individually... Didn't I say don't be lazy?! Also it can be useful to get to a eager, non-lazy font whether or not it was originally loaded lazily, so I added an ensureDecompiled method that decompiles all the tables and calls ensureDecompiled for those (e.g. cmap, glyf and otData-driven tables like GSUB, GPOS, etc.) that respect the lazy attribute.
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i'm gonna add tests but first want to gather feedback |
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There's a lot of code out there that doesn't do What about the oposite: have a method that explicitly deompiles all? TTFont was always about lazy loading, the |
wait, but lazy=False is opt-in, i'm not changing the default behavior of lazy=None.. |
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If you grep the code, right now the only difference between lazy=None (default) and lazy=False is in glyf table, which explicitly checks I would argue that giving lazy=False a new meaning of load everything eagerly upon opening the font can be useful and won't disrupt much existing workflows. If one bothered to set lazy=False to begin with, they definitely are willing to pay the performance hit for whatever reason. Anyway, if lazy=False as "load everything upfront" turns out to be controvertial, I'm willing to only add the new ensureDecompiled method and keep the current behavior unchanged. |
one has to call TTFont.ensureDecompiled to load everything
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I removed the auto-load-all-tables-if-lazy-is-false. One has to call |
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(Not a big fan of the "return self for expression convenience" pattern. JS does this all over the place, but eg. Python's |
This reverts commit 61e7b29.
hm ok, I reverted |
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I see you've already added the I find using |
makes it more useful for constructing generic traversals of trees of otTables
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@justvanrossum the last commit ab8fc32 is technically not required for this PR but it can be handy knowing the name and index of a subtable when traversing a tree of otTables. I can make it into its own PR if you prefer. |
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I'm enthused about lazy=False actually decompiling (and not being default). I loaded with lazy=False, checked isLoaded on the TTFont's keys, and had a wtf moment when it reported nothing was loaded. |
While attempting to tackle glyph reordering in #2060, I needed a way to say "decompile everything in the font". The lazy=False unfortunately does not exactly do what it says to be doing, and that's confusing for people who are not familiar with the fonttools internals (some colleagues did stumble on this). Not only one has to set lazy=False, but one also has to iterate over all the tables and actually decompile them using silly loop like:
A quick recap about
TTFont.lazyattribute. It has three states: it defaults to None, and can be optionally be set to True or False.When it is set to True, the font keeps a reference to the original input file (inside its SFTNReader); when it's None (or False), it copies the raw bytes of the input files to in-memory stream (allows overwriting input, or reading from unseekable streams). A TTFont decompiles a given table only when requested (in
__getitem__) -- confusingly even when lazy=False.Then, some tables take into account the lazy attribute to decide whether to load or not all their data upfront. In particular:
BaseTable.__getattr__triggeres decompiling upon getting any attribute); they are fully decompiled if lazy is None (default) or False.What this PR proposes to change is:
have(decided to reverted this change)TTFont(path, lazy=False)immediately decompile all the tables' data, everything, like it says on the tin, so one doesn't need to then also decompile individual tables;ensureDecompiledmethod to TTFont, cmap, glyf and the otTables that allows to un-lazify them even when a font had been loaded with lazy=True or None; they get the same as opening it with lazy=False.