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

[Sergey Bylokhov]

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.


-- 
Best regards, Sergey.