[OpenJDK 2D-Dev] [9] Review request for 8160124 SunGraphics2D.hitClip() can give wrong result for floating point scale

[Alexandr Scherbatiy]

On 6/24/2016 1:14 AM, Phil Race wrote:
> So .. question to Alexandr :
> JComponent.paintChildren() is the only place in the JDK that consumes 
> this API.
> Is this causing a particular problem with Swing hi-dpi - other than 
> repainting in cases that maybe didn't need it ?

    This is used, for example, for internal frames dragging. An internal 
frame is just copied as a whole image so only small areas near the 
internal frame should be repainted.
    The current case where hit hitClip() fails for scale 1.5 causes 
whole internal frame repainting on Windows with 150% scale.
    Swing can implement its own clip intersection algorithm for this 
special case.

    I can close the JDK-8160124 as not an issue.

   Thanks,
   Alexandr.

>
> -phil.
>
>
>
> On 6/23/2016 3:00 PM, Jim Graham wrote:
>> Since "return true" would be a compliant implementation of 
>> Graphics.hitClip(), this is not a bug...
>>
>> Read the documentation, it is allowed to use fast math that can 
>> return true when technically the answer is false...
>>
>>             ...jim
>>
>> On 6/23/16 5:04 AM, Alexandr Scherbatiy wrote:
>>>
>>> Hello,
>>>
>>> Could you review the fix:
>>>   bug: https://bugs.openjdk.java.net/browse/JDK-8160124
>>>   webrev: http://cr.openjdk.java.net/~alexsch/8160124/webrev.00
>>>
>>>   Let's set the clip [x=5, y=5, width=5, height=5] to a graphics and 
>>> call the hitClip() with the passed rectangle [x=0,
>>> y=0, width=5, height=5].
>>>
>>>   The result is false for the graphics with scale 1 and true if the 
>>> scale is floating point 1.5.
>>>
>>>   This is because the transformed clip which has floating point 
>>> bounds [7.5, 7.5, 7.5, 7.5] for the scale 1.5 has bounds
>>> with rounded down upper-left  and rounded up lower-right corners [7, 
>>> 7, 8, 8] which now intersects with the transformed
>>> rectangle [0, 0, 7.5, 7.5].
>>>
>>>   The proposed fix adds additional check for the user clip and the 
>>> user rectangle intersection if the intersection with
>>> the region clip passes.
>>>
>>>  Thanks,
>>>  Alexandr.
>>>
>>>
>