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

[Andrew Brygin]

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.