[OpenJDK 2D-Dev] RFR: 8238942: Rendering artifacts with LCD text and fractional metrics

[Philip Race]

Ignore the comment. I should have deleted that (and will before pushing).

Since we are adding padding on the left, to render the rightmost pixel
of the unpadded image, we need to extend the width by one pixel.

But the padding means that the image (as seen by the user)
is now being rendered one pixel to the right of where it should be.

So we need to adjust the rendering origin of the glyph one pixel to the 
left.

-phil.

On 2/11/20, 10:53 PM, Sergey Bylokhov wrote:
> Hi, Phil.
>
> Could you please clarify these lines, from the patch it
> is unclear what they should do. "Why"
>
> + glyphInfo->topLeftX -= 1;
> + // WHY NOT ADD ?
> + glyphInfo->width += 1;
>
> On 2/11/20 8:15 pm, Philip Race wrote:
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8238942
>> webrev: http://cr.openjdk.java.net/~prr/8238942/
>>
>> As discussed in the bug, we are missing padding in the code that takes
>> an LCD glyph from freetype and caches it in the 2D glyph cache.
>>
>> This padding is used in subpixel positioning with fractional metrics on.
>>
>> I've run automated regression tests as well as doing extensive manual 
>> testing
>> and so far it looks fine. A specific regression test is hard because 
>> the visual
>> artifacts manifest rarely and even so are not easy to test.
>> There should be plenty of time in JDK 15 for this to bake.
>>
>> -phil.
>
>