[OpenJDK 2D-Dev] [9] request for review: 8041465: BMPImageReader read error using ImageReadParam with set sourceRectangle

[Andrew Brygin]

Hello Sergey,

   my preference is to leave the seek(bitmapStart) in the read() method
   in order to reduce potential overhead because readHedaer() is called
   very often.

Thanks,
Andrew

On 9/8/2014 7:31 PM, Sergey Bylokhov wrote:
> Hi, Andrew.
> I am not an expert in this area, but probably the bug can be fixed in 
> the readHeader itself? Because currently it call 
> iis.skipBytes(bitmapOffset) at the end only for the first time.
>
> On 03.09.2014 16:23, Andrew Brygin wrote:
>> Hello,
>>
>>  could you please review a fix for CR 8041465?
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8041465
>> Webrev: http://cr.openjdk.java.net/~bae/8041465/9/webrev.00/
>>
>>  The problem happens if we perform multiple read operations from
>>  a source which is set only once. For instance, we can try to read
>>  image in several tiles.
>>
>>  The root case of the problem is that we set stream position
>>  to the start of raster data only once: when we complete
>>  the processing of BMP header.  A peculiarity of BMP format
>>  is that raster data can be stored in reverse order, so if we
>>  request few leading scanlines first, then we skip rest of raster
>>  data, and subsequent read command does not copy anything to the
>>  destination buffer, because we never re-set the stream position
>>  to the start of bitmap.
>>
>>  Suggested fix just saves the bitmap's start postilion and seeks
>>  the stream to to it each time when we read image. This change
>>  makes the BMP reader behavior exactly same as other standard plugin
>>  demonstrate.
>>
>>  Supplied regression test demonstrates the problem.
>>
>>  Please take a look.
>>
>> Thanks,
>> Andrew.
>
>