[OpenJDK 2D-Dev] RFR: 8177393: Result of RescaleOp for 4BYTE_ABGR images may be 25% black

[Philip Race]

Some review discussion with Jim is in the bug report comments.

Updated webrev to address the minimal set of issues :
http://cr.openjdk.java.net/~prr/8177393.1/

-phil.

On 5/18/17, 3:32 AM, Prasanta Sadhukhan wrote:
>
> Looks good to me. [Checked 8080287 also works ok with this change]
>
> Regards
> Prasanta
> On 5/17/2017 11:14 PM, Phil Race wrote:
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8177393
>> Webrev: http://cr.openjdk.java.net/~prr/8177393/
>>
>> I have updated the bug report with a long evaluation and some additional
>> explanation of the proposed fix. I don't intend to duplicate all that 
>> here
>> so please go read it there. The following is a much briefer summary.
>>
>> We are ending up in medialib native code that cannot interpret the 
>> Java 2D child raster
>> it is handed. The child raster was an attempt to prevent rescaling of 
>> the alpha channel.
>>
>> The proposed fix avoids creating that child raster and instead 
>> creates a LookupOp
>> which has an explicit lookup table for the alpha channel that does 
>> the identity lookup.
>>
>> The fix has a couple of other updates.
>> (1) the "canUseLookupOp()" method now checks that the DataBuffer is
>> something that the medialib code used by LookupOp can handle.
>> This would have fixed the bug by itself although at the expense of always
>> falling back to slow Java code in RescaleOp. However it is still 
>> needed in
>> case the application itself supplies a child raster.
>>
>> (2) The slow path in RescaleOp turns out to have the same bug that I 
>> think
>> was seen in some other bug report or fix. It is always re-scaling 
>> alpha as
>> well as colour components. I fixed that too.
>>
>> Since the fix is entirely confined to RescaleOp any consequences - 
>> good or bad - are limited.
>>
>> I ran the few regression tests we have that cover RescaleOp and also 
>> checked Java2Ddemo.
>>
>> The commented out cases in the new regression test are to be handled 
>> under a different bug ID.
>>
>> -phil.
>
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