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

[Jim Graham]

I suspect the answer is that as long as Swing/AWT use APIs that have integer coordinates, there will be cases where this 
hit testing might be able to know the answer in floating point coordinates, but lose the ability to answer accurately 
when everything is turned into integers - which often involves ceil/floor operations that expand bounding boxes.  In the 
case of 150% rendering for Windows, sometimes you can't accurately describe the pixels you will be rendering with enough 
precision in integer coordinates...

			...jim

On 6/23/16 3:14 PM, 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 ?
>
> -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.
>>>
>>>
>