Hi, Phil.
I have only the question about the new comment:
340 // Let's not adjust the metrics of any glyph that is zero advance.
341 if (slot->linearHoriAdvance == 0) {
342 return;
343 }
The comments said that we do not want to adjust the metrics and return, but we
already adjusted it a little bit before:
335 slot->metrics.width += extra;
336 slot->metrics.height += extra;
I do not know the exact reason to check linearHoriAdvance at line 341, but then why we
skip the check of "linearVertAdvance"?
On 4/15/20 2:00 pm, Philip Race wrote:
Bug : https://bugs.openjdk.java.net/browse/JDK-8233006
Webrev : http://cr.openjdk.java.net/~prr/8233006
The bug here is that the freetype function for synthesising bold is not ready
to handle rotation.
In the process I noticed it did not adjust the advance used by the fractional
metrics case,
even though the outline is bolded.
Also, in what seems to be a completely wrong thing to do, freetype would
widen the advance of glyphs which have zero advance.
So I decided that the best thing to do was to write our own.
A chunk of the heavy lifting - widening the outline - is still done by freetype
but there were a lot of details to get right and test.
I wrote a test to visualise the problem but the actual test checks by looking
at the bounding rectangle of the drawn pixels and compares its height to
the declared metrics of the font, failing if they disagree by too much.
Note that the code path is only exercised when synthetic bolding is needed.
So real bold fonts don't test this code.
Since there's not an easy way to say which fonts have real bold, I decided the
test should use a BOLD version of every font on the system, which on almost
all systems will test some significant number of such cases.
I kept the UI for visualising as it will be useful for later debugging of
failures.
Also it made me notice that the case where the text was not rotated at all was
drawing shorter than all the other cases.
I traced this back to the fix for 8203485 which added a macro FT26Dot6ToInt
and used it to get the integer advance in the unrotated, integer metrics case.
The idea there wasn't completely wrong, but I don't think it was completely
right either.
I got rid of the macro and instead used the same FT26Dot6ToFloat macro as used
in the rotation cases. So we now return the exact floating point value to the
calling
Java code. That then can round appropriately as it needs to. This fixed the
inconsistency
and the test for 8203485 still passes as do all other tests.
This change will likely lead to some cases where unrotated advances now round
up one pixel wider,
but so far it looks correct to me. They'll be restored to something more like
what they were
before 8203485, since that removed rounding and added truncation instead to fix
a problem
with the rounding being incorrect for rotations because it could round down
when it should round up.
Now we just let the Java code handle it.
I've run these tests on all platforms and they pass. Mac isn't using this
freetype path so it is not affected
but it is still good to know the tests pass there ...
-phil
--
Best regards, Sergey.
