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

[Andrew Brygin]

corrected:

 47     static final Font fnt = new Font(Font.SERIF, Font.PLAIN, 12);

Updated webrev: http://cr.openjdk.java.net/~bae/8203485/webrev.01/

Thanks,
Andrew

> On May 22, 2018, at 7:26 PM, Philip Race <philip.race at oracle.com> wrote:
> 
> 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
>>