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

[Jim Graham]

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
>
>
>