[graphics] [9] Review request for 8155903: Crash while running imported/w3c/canvas/2d.gradient.interpolate.overlap2.html

[Arunprasad Rajkumar]

Hello Jim,

Thanks for your suggestions. As of now I taking an easy way to fix the 
issue, New changes are available at 
http://cr.openjdk.java.net/~arajkumar/8155903/webrev.02

I couldn't write a reliable test case using public javafx APIs, the 
behavior is intermittent. However I could consistently produce the issue 
using our DRT internal test case which is based on W3C functional test[1].

[1] 
http://w3c-test.org/2dcontext/fill-and-stroke-styles/2d.gradient.interpolate.overlap2.html

Thanks,
Arun

On 5/5/2016 11:51 PM, Jim Graham wrote:
> Hi Arun,
>
> The change you made to the calculateSingleArray method looks like it 
> produces a bad array of color stops for the case where Imin is 0.  You 
> should fall into the calculateMultipleArray method instead which 
> should not have any trouble with zero length intervals.  At that point 
> you don't have to have any code in calculateSingleArray that deals 
> with Imin being zero because that can be part of its calling contract.
>
> That is the quick fix.
>
> The harder fix that would let us maintain speed when there is a zero 
> interval would be to teach the code what to do in that special case. 
> Basically a zero interval means that we have a case where approaching 
> the interval point from the left is interpolating towards colorA, but 
> leaving that point from the right is interpolating from colorB, with a 
> sudden transition between those 2.  In that case, a zero interval 
> shouldn't affect the Imin, since the Imin is trying to determine the 
> size of each interpolated region and we don't interpolate across a 
> zero-sized interval.  So, the scan for Imin would simply ignore zero 
> length intervals.  Later, the code that populates the array in the 
> calculateSingleArray function would know that the zero length interval 
> simply means swap in a new "from color" without any actual interpolation.
>
> Getting that harder fix right would require a lot of testing, so it 
> may be better to do the quick fix now to stop the exceptions and then 
> deal with the optimization as a tweak filed for later...
>
>             ...jim
>
> On 05/05/2016 01:57 AM, Arunprasad Rajkumar wrote:
>> Hello Jim,
>>
>> Please review the below patch.
>>
>> JIRA: https://bugs.openjdk.java.net/browse/JDK-8155903
>>
>> Webrev: http://cr.openjdk.java.net/~arajkumar/8155903/webrev.01
>>
>> Issue: Divide by zero while adding multiple gradient stops at same 
>> offset.
>>
>> Regards,
>> Arun
>>
>>
>>