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We only open one instance of freetype per document. We therefore
have to ensure that only 1 call to it takes place at a time. We
introduce a lock for this purpose (FZ_LOCK_FREETYPE), and arrange
to take/release it as required.
We also update the font context so it is properly shared.
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This is a significant change to the use of locks in MuPDF.
Previously, the user had the option of passing us lock/unlock
functions for a single mutex as part of the allocation struct.
Now we remove these entries from the allocation struct, and
make a separate 'locks' struct. This enables people to use
fz_alloc_default with locking.
If multithreaded operation is required, then the user is
required to create FZ_LOCK_MAX mutexes, which will be locked
or unlocked by MuPDF calling the lock/unlock functions within
the new fz_locks_context structure passed in at context creation.
These mutexes are not required to be recursive (they may be, but
MuPDF should never call them in this way). MuPDF avoids deadlocks
by imposing a locking ordering on itself; a thread will never take
lock n, if it already holds any lock i for which 0 <= i <= n.
Currently, there are 4 locks used within MuPDF.
Lock 0: The alloc lock; taken around all calls to user supplied
(or default) allocation functions. Also taken around all accesses
to the refs field of storable items.
Lock 1: The store lock; taken whenever the store data structures
(specifically the linked list pointers) are accessed.
Lock 2: The file lock; taken whenever a thread is accessing the raw
file. We use the debugging macros to insist that this is held
whenever we do a file based seek or read. We also insist that this
is never held when we resolve an indirect reference, as this can
have the effect of moving the file pointer.
Lock 3: The glyphcache lock; taken whenever a thread calls freetype,
or accesses the glyphcache data structures. This introduces some
complexities w.r.t type3 fonts.
Locking can be hugely problematic, so to ease our minds as to
the correctness of this code, we introduce some debugging macros.
These compile away to nothing unless FITZ_DEBUG_LOCKING is defined.
fz_assert_lock_held(ctx, lock) checks that we hold lock.
fz_assert_lock_not_held(ctx, lock) checks that we do not hold lock.
In addition fz_lock_debug_lock and fz_lock_debug_unlock are used
on every fz_lock/fz_unlock to check the validity of the operation
we are performing - in particular it checks that we do/do not already
hold the lock we are trying to take/drop, and that by taking this
lock we are not violating our defined locking order.
The RESOLVE macro (used throughout the code to check whether we need
to resolve an indirect reference) calls fz_assert_lock_not_held to
ensure that we aren't about to resolve an indirect reference (and
hence move the stream pointer) when the file is locked.
In order to implement the file locking properly, pdf_open_stream
(and friends) now lock the file as a side effect (because they
fz_seek to the start of the stream). The lock is automatically
dropped on an fz_close of such streams.
Previously, the glyph cache was created in a context when it was first
required; this presents problems as it can be shared between several
contexts or not, depending on whether it is created before the
contexts are cloned. We now always create it at startup, so it is
always shared.
This means that we need reference counting for the glyph caches.
Added here.
In fz_render_glyph, we take the glyph cache lock, and check to see
whether the glyph is in the cache. If it is, we bump the refcount,
drop the lock and returned the cached character. If it is not, we
need to render the character.
For freetype based fonts we keep the lock throughout the rendering
process, thus ensuring that freetype is only called in a single
threaded manner.
For type3 fonts, however, we need to invoke the interpreter again
to render the glyph streams. This can require reentrance to this
routine. We therefore drop the glyph cache lock, call the
interpreter to render us our pixmap, and take the lock again.
This dropping and retaking of the lock introduces a possible race
condition; 2 threads may try to render the same character at the
same time. We therefore modify our hash table insert routines to
behave differently if it comes to insert an entry only to find
that an entry with the same key is already there.
We spot this case; if we have just rendered a type3 glyph and when
we try to insert it into the cache discover that someone has beaten
us to it, we just discard our entry and use the cached one.
Hopefully this will seldom be a problem in practise; to solve it
properly would require greater complexity (probably involving
spotting that another thread is already working on the desired
rendering, and sleeping on a semaphore until it completes).
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On extreme downscales, the weights for each pixel can all round to
zero; this results in no weights being stored at all, and causes
either an exception or a SEGV. The simple fix is to ensure that the
first pixel that's actually in range (and there will always be one)
always has a weight of at least 1.
Thanks to malc for finding the test cases that lead to this bugfix.
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fz_draw_fill_image_mask was improperly nesting group start/ends, by
calling fz_knockout_start at the top, and then fz_knockout_start
again at the end. Changing this latter one to fz_knockout_end
solves the problem.
Also tweak the debugging code slightly to give more readable results.
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The cluster testing of MuPDF repeatedly crashes on
pdf/PDF_1.7_FTS/fts_20_2008.pdf. Investigation shows this is because
we fail to write the newly allocated mask back to the graphics
state stack when starting a clip_stroke_text drawing operation.
This causes later pops to fall over.
Simple fix.
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Modified version of Sumatras patch. Thanks for this.
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The ARM optimised code relied on the size of the weights structure
which was changed by the addition of a new member as part of the
patch scaling changes. Fix the code here, and add a note to the
structure in the hopes that this will avoid such breakages happening
in future.
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Both Zeniko and Malc have said that this causes problems.
Following a hint from malc, the following command causes the
assert to trigger:
win32/Debug/pdfdraw.exe -r0.3 -o out.png ../MyTests/pdf_reference17.pdf 1143
I suspect it's because of the extreme resolution, and the round_rect
call. At any rate, disabling the assert is of no real import.
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When scaling a bitmap, currently we always scale the entire bitmap,
even if we only need a small section of the result.
This patch changes the code to take an optional 'clip' bbox, and
only scales as many pixels as are required to generate the required
output region.
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This way both pixmaps for rendering and image data are top-down.
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This reverts commit 08e84b18e5c1dbe8f3d32dd0aeb4b4c43debce9f.
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When scaling a bitmap, currently we always scale the entire bitmap,
even if we only need a small section of the result.
This patch changes the code to take an optional 'clip' bbox, and
only scales as much of the input as as required for this output
region.
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When we moved over to a context based system, we laid the foundation
for a thread-safe mupdf. This commit should complete that process.
Firstly, fz_clone_context is properly implemented so that it
makes a new context, but shares certain sections (currently
just the allocator, and the store).
Secondly, we add locking (to parts of the code that have
previously just had placeholder LOCK/UNLOCK comments). Functions
to lock and unlock a mutex are added to the allocator structure;
omit these (as is the case today) and no multithreading is
(safely) possible. The context will refuse to clone if these are
not provided.
Finally we flesh out the LOCK/UNLOCK comments to be real calls of
the functions - unfortunately this requires us to plumb fz_context
into the fz_keep_storable function (and all the fz_keep_xxx
functions that call it). This is the largest section of the patch.
No changes expected to any test files.
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XPS differs from PS/PDF/etc in the way it handles miters; rather than
simply converting a miter that's overly long to a bevel, it truncates
it at the miter limit. As such it needs to be handled correctly.
For clarity, expose new enumerated types for linejoins and linecaps,
and use these throughout code.
When we upgrade our freetype, we can move to using proper xps mitering
in that too.
Add new fz_matrix_max_expansion function to return a safer expansion
value that works in the case where we scale up in one direction and
down in another.
In the xps path drawing code, avoid generating unnecessary linetos.
Thanks to Zeniko for spotting these and providing implementations.
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Inspired by Sumatras gdi devices need for such a function expose
the blending functions. Note that we produce unsigned char's
where Zenikos original produces ints, but it's otherwise
identical.
This requires us to make various knockon changes throughout the code
from int to unsigned char, none of which should make any difference
at all - I hope!
We reserve the right to change/amend this function in future to
operate on blocks of pixels (or pixels in different colorspaces)
(or anything else we think of) in future.
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Take on a modified version of Zenikos patch; only take the quick
exit if the whole dash length is small, or if the dash_length
scaled up by the maximum possible scale in the ctm is less than
1/2 a pixel.
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Various fixes to avoid overflow problems, division by zeros, use
of uninitialised variables etc. All from/suggested by Zenikos patch.
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Thanks to Zeniko for pointing this out.
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Only create a shape if we need to.
Correctly cleanup, thus avoiding a double free of mask later on.
Thanks to Zeniko for spotting these.
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As we create clips/transparency groups etc, we maintain a stack of
draw device states.
Here we change this from having a 'current' state, and storing changes
on the stack to always keeping the complete current state on the head
of the stack. This should make error cleanup easier, as well as being
conceptually easier to follow (for me at least).
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When starting to tile, create a shape plane if one exists.
When finishing tiling, plot the shape plane back too.
This solves the SEGVs. Something isn't quite right with the blending
colours on part of this file though.
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Testsseem to indicate that this works, and gives noticable
improvements. Enabling by default.
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The shape plane was being incorrectly offset from the dest plane.
This could have caused SEGVs or incorrect results when blending
back.
This solves the hivemind.pdf iphone being clipped on the right hand
side.
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More work on MuPDFs blending support. This seems to get l16.pdf
working pretty well. Fuller testing required to know if we get
everything right, but the maths now makes as much sense as it
ever has to me, and seems to track what gs does (more or less,
in that we don't use group alpha and gs does).
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As Zeniko correctly points out in bug 692593, I had incorrectly
used hp[n1] when I should be using hp[0] at various points.
Hopefully that bug should be solved in it's entirety now with
the previous commit.
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Restrict images to the size of the shape when blending back.
This seems to solve the problem; leaving code disabled until full
tests complete.
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The new fz_malloc_struct(A,B) macro allocates sizeof(B) bytes using
fz_malloc, and then passes the resultant pointer to Memento_label
to label it with "B".
This costs nothing in non-memento builds, but gives much nicer
listings of leaked blocks when memento is enabled.
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Fixes for leaks (and SEGVs, division by zeros etc) seen when
Memsqueezing.
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Also: use 'cannot' instead of 'failed to' in error messages.
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The code attempts to spot cases where a pattern tile is so large that
only 1 repeat is visible. Due to rounding errors, this test could
sometimes fail, and (on badly formed files) we'd attempt to allocate
huge pixmaps.
The fix is to allow for rounding errors.
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In builds that support configurable layers of antialiasing, move
the variables that control this into the context. This makes it
possible to safely use different levels of antialiasing in different
threads.
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Previously, we had a hardwired 96 element stack for clipping/group
nesting etc. If this was exceeeded during rendering we would give
an error.
Now we allow for that stack to be extended dynamically at runtime.
If the stack extension fails, we will give an error and die.
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