[OpenJDK 2D-Dev] RFR: 8203485: [freetype] text rotated on 180 degrees is too narrow

[Philip Race]

Fix sounds good.

The test has a bug
   47     static final Font fnt = new Font("Time New Roamn", Font.PLAIN, 1).deriveFont(12.0f);

"Roamn" should be "Roman".

But since Linux is very unlikely to have that font, I think you should 
use Font.SERIF instead.

Actually I am unclear why you need to use deriveFont and can't
test this with the constructor taking int of 12.

-phil

On 5/22/18, 8:50 AM, Andrew Brygin wrote:
> Webrev: http://cr.openjdk.java.net/~bae/8203485/webrev.00/
> Bug: https://bugs.openjdk.java.net/browse/JDK-8203485
>
> With freetype, text rotated on 180 or 270 degrees is too narrow.
> Attached test case and screenshots demonstrate the problem.
>
> The problem is caused by the rounding applied to the cases of vertical
> and horizontal text, see freetypeScaler.c, lines 768 and 773:
> http://hg.openjdk.java.net/jdk/client/file/80a5ff734fcd/src/java.desktop/share/native/libfontmanager/freetypeScaler.c#l768
> http://hg.openjdk.java.net/jdk/client/file/80a5ff734fcd/src/java.desktop/share/native/libfontmanager/freetypeScaler.c#l773
>
> The rounding routine is defined as ROUND(x) ((int) (x+0.5)) (see line 48),
> and it gives incorrect results for negative arguments.
>
> For example, say glyph advance is 8, and we render it without rotation,
> and with rotation on 180 degrees. In these cases, we get ROUND(8) = 8,
> whereas for 180 degrees we get ROUND(-8) = -7. This rounding error
> leads to decrease of the width of the rendered text.
>
> For the case of integer metrics, we can expect that FT26.6 advances
> produced by freetype are integer, i.e. fractional part (lower 6 bits)
> is zero. So, we can convert them to glyph info values without floating
> point division, just by using integer shift. In this case, there is no
> need to round the floating point value to integer, and there is no need
> to care about sign of the argument.
>
> Thanks,
> Andrew
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