[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 prasanta.sadhukhan at oracle.com
Wed Jul 29 18:21:45 UTC 2015

Hi Jim,

Thanks for your comments. My observations inline..
On 7/29/2015 9:22 AM, Jim Graham wrote:
> Hi Prasant,
> Can you check what the ImagingLib call at line 401 will do if we have 
> the case that scaleConst != length?  We used to modify "this.length" 
> at line 350, but now we no longer do that (because it was wrong), but 
> the code in ImagingLib may have depended on that.
As far I see, ImagingLib does not do anything for RescaleOp so this 
change will not have any effect. It has functionality for LookupOp, 
AffineTransformOp and ConvolveOp and just fall back to Java for 
RescaleOp to do the needful.
> Similarly, at line 445 we call this.filter(raster, raster) which 
> expects this.length to be an appropriate value - and if it could see 
> the value of scaleConst that we've calculated, that value would be 
> correct, but it is expecting that value to have been passed through 
> via the this.length field.  We must not modify this.length so we need 
> a way to say "filter the rasters, but using these other constants that 
> I've calculated, not the ones you see in the fields.  That is what I 
> was referring to when I said that the implementation part of 
> filter(Raster, Raster) should be split out into a method that takes 
> parameters from one of the 2 front end methods.  We need to do that 
> here so that filter(Image, Image) can tell it to convert only 
> scaleConst number of bands without having to modify the length field.
Have split filter(Raster, Raster) into implementation method for 
filer(Image,Image) to call with scaleConst.
> Lines 378 and 383 - origDst is used to convert the rescaled raster 
> back to the color space of the original destination.  But, at line 378 
> we've already replaced the original destination with a newly created 
> one so we are not saving the original destination, we are just making 
> a second reference to the dst.  Later, at line 478, we convert dst to 
> dst which is a NOP.
I guess origDst is replaced by newly created one to avoid a scenario 
whereby filter(Image, Image dst=null) is called so needToConvert will be 
false and so line 478 will not be executed and thereafter if we return 
origDst at end, we will be returning null. I tried to circumvent this by 
storing origDst at start but I again store the rescaled dst back to 
origDst (in case if origDst is null ) which is returned at the end.
> Lines 408-440 - we can put a test for "if (!scaleAlpha)" around the 
> entire block rather than testing it separately in each of the 
> src/dest.hasAlpha() blocks.
> Line 447 - we should not copy the alphas if scaleAlpha is true, should 
> we?  The scaling done in the raster should have already copied and 
> scaled them and you'd be replacing them with unscaled copies of the 
> original...
Have taken care of this.
Please find the modified webrev here:

Please let me know if this is ok.

> ...jim
> On 6/30/15 3:38 PM, Jim Graham wrote:
>> The backup code if ImagingLib does not do the work is to forward the
>> request to the filter(Raster, Raster) method which again tests length
>> and requires it to be == src.getNumBands().  An instance to this Op is
>> also passed to ImagingLib in that method and it's not clear what will
>> happen if length doesn't match when that happens either.  It may simply
>> ignore the operation and we end up in the backup code, or it may get an
>> exception.  In any case, since the length field was not modified by
>> filter(Bimg, Bimg), we've changed the conditions in the downstream code.
>> What I'd generally like to see in cases like this is that the public
>> methods do validation and then they pass only validated information to
>> helper routines which are clearly private.  For things like "in this
>> case we don't want to operate on all of the bands of the image", it
>> would be nice if the helper routines could be told to work on explicitly
>> defined bands rather than having to compute child rasters with subset
>> bands.  Doing all of that would take quite a bit of work, but perhaps we
>> can at least do the following:
>> - provide a filterRaster() helper method that filter(Raster x 2) and the
>> backup case for filter(Bimg x 2) both call after validation
>> - the filterRaster() helper method would take a length parameter and
>> ignore the field value
>> - ImagingLib interfaces may have to be upgraded as well to take a length
>> parameter, I haven't looked at ImagingLib yet to see how it would be
>> affected by these changes
>> That much should be fairly easy to arrange, and in doing that we may
>> discover that it would be easy to have ImagingLib take a list of subset
>> bands which might help us avoid doing all of the createChildRaster calls
>> in filter(Bimg)...
>>              ...jim
>> On 6/28/2015 11:44 PM, prasanta sadhukhan wrote:
>>> 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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