On 4/16/20, 6:31 AM, Sergey Bylokhov wrote:
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;
That is stored in metrics but it is the bounding box of the glyph image.
So we definitely need to adjust that before we return since we widened
the glyph outline.
I do not know the exact reason to check linearHoriAdvance at line 341,
but then why we skip the check of "linearVertAdvance"?
A few reasons.
First, you'd need a font with vertical layout support (very rare) and
for JDK to then actually support vertical text layout for it to matter -
so not needed.
Second, it is not clear if we'd want to do it even if we had such
support. We weren't previously getting scaled
linear horizontal advance from freetype and it was "OK". Just a tiny bit
more less spaced than ideal because bold glyphs are wider.
With vertical it is less clear to me that you'd scale the advance in the
same way. So until such a day comes it is fine as it is.
Third, freetype didn't adjust it either, just like it wasn't adjusting
the horizontal case.
Even this line below .. I am not sure is used for anything ..
+ slot->metrics.vertAdvance += extra;
.. but freetype added it, so I did so too to be safe.
-phil.
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
