[OpenJDK 2D-Dev] Review Request for bug (JDK-8080287): The image of BufferedImage.TYPE_INT_ARGB and BufferedImage.TYPE_INT_ARGB_PRE is blank

[prasanta sadhukhan]

Hi Jim,

I was following the RescaleOp spec where it states
/The number of sets of scaling constants may be one, in which case the 
same constants are applied to all color (but not alpha) components/
which is taken care by
/if (numSrcColorComp == scaleConst || //*scaleConst == 1*//) {//
//*scaleAlpha = false*;//
//        }//
//Otherwise, the number of sets of scaling constants may equal the 
number of Source color components, in which case no rescaling of the 
alpha component (if present) is performed/
/if (*numSrcColorComp == scaleConst* || //scaleConst == 1//) {//
//*scaleAlpha = false*;//
//        }//
////If neither of these cases apply, the number of sets of scaling 
constants must equal the number of Source color components plus alpha 
components, in which case all color and alpha components are rescaled

//For Rasters, rescaling operates on bands. The number of sets of 
scaling constants may be one, in which case the same constants are 
applied to all bands, or it must equal the number of Source Raster bands. /
which is taken care by above check.
Earlier, we had

int[] bands = new int[numBands-1];

which omitted the last color bands (which I could not find in the spec 
if that is what we should do). So, I changed to

int[] bands = new int[numSrcColorComp];

Regards
Prasanta

On 6/25/2015 3:17 AM, Jim Graham wrote:
> Hi Prasanta,
>
> I just realized that this method uses filter(Raster, Raster) to do its 
> work and so some of these changes may affect how it communicates with 
> that method.  This will take some time to look through all of the 
> interactions.  In particular, the code that modified the length 
> parameter, while still wrong in the long run, may have had the side 
> effect of making some of the operations succeed by making sure the 
> right preconditions existed for the raster case...
>
>             ...jim
>
> On 6/23/15 11:30 PM, prasanta sadhukhan wrote:
>> Hi Jim,All
>>
>> I have modified the code following your comments. Please find the
>> modified webrev:
>> http://cr.openjdk.java.net/~psadhukhan/8080287/webrev.02/
>> Could you please review this?
>>
>> Regards
>> Prasanta
>> On 6/23/2015 2:03 AM, Jim Graham wrote:
>>> In reading through this I notice that at line 349 the filter code can
>>> permanently change the nature of the RescaleOp.  It should use a local
>>> copy of the length field if it is going to reinterpret it on the fly
>>> like that.
>>>
>>> Also, at line 348 - shouldn't it do something if length > numBands,
>>> but the source does not have alpha?  Or is this due to the fragile
>>> tests for "length == numBands+1" below which use that to determine if
>>> some special processing should be done for alpha? The handling of the
>>> relationship between length, numBands and alpha in general seems to be
>>> very fragile and full of assumptions about how the setup code managed
>>> those values without any code comments saying "we leave these
>>> variables in this relationship to indicate that we need to do X, Y, or
>>> Z".  I'd prefer various conditions to be reflected in appropriate
>>> boolean variables that are reasonably descriptive rather than
>>> undocumented assumptions about how length relates to numBands.  Also,
>>> numBands should probably be renamed to numColorBands to avoid any
>>> issues such as what Andrew noted below.
>>>
>>> The test at line 397 seems backwards.  Shouldn't it be "(numBands+1 ==
>>> length)"?  What exactly is it testing?  It looks like it is deciding
>>> if it should eliminate alpha from the scaling loops since "length==1"
>>> is defined to only modify the colors, but then it subsets the color
>>> bands which means if you supply only one scale then you scale all but
>>> the alpha band and also all but one of the color bands.  Or am I
>>> misreading something?
>>>
>>>             ...jim
>>>
>>> On 6/22/2015 2:58 AM, Andrew Brygin wrote:
>>>> Hello Prasanta,
>>>>
>>>>   I have couple comments regarding the fix.
>>>>
>>>> *  lines 408 - 420 and lines 438 - 444.
>>>>      Here you are obtaining the source and destination rasters for all
>>>> bands (colors + alpha).
>>>>      However, it is already done on the lines 391 and 392.
>>>>       Could you please clarify a purpose of this change?
>>>>
>>>> * line 399: here 'numBands' represents number of color bands in the
>>>> source image (see line 329).
>>>>     So, the last color band is excluded from processing (for 
>>>> example, in
>>>> RGB image you get raster
>>>>     that contain only R and G bands).
>>>>
>>>> * you have created a manual test. Probably an automated test is a bit
>>>> more
>>>>     convenient option here.
>>>>     Also, there seems to be no need for a jpg image for this test. A
>>>> source image
>>>>     with color strips is much more useful.
>>>>
>>>> Thanks,
>>>> Andrew
>>>>
>>>> On 6/22/2015 12:36 PM, prasanta sadhukhan wrote:
>>>>> Hi ,
>>>>>
>>>>> Please review a fix for this issue:
>>>>> It was found that RescaleOp on image with different alpha cannot
>>>>> render the image as there is a particular flaw in RescaleOp
>>>>> implementation whereby the source alpha channel is never
>>>>> transferred to the destination if the rescale op is performed in java
>>>>> (or is never populated, if source image has no alpha channel),
>>>>> resulting in fully transparent destination image.
>>>>> Fix is to make sure the unscaled source alpha is transferred to
>>>>> destination alpha channel.
>>>>>
>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8080287
>>>>> webrev: http://cr.openjdk.java.net/~psadhukhan/8080287/webrev.00/
>>>>>
>>>>> Regards
>>>>> Prasanta
>>>>
>>

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