[OpenJDK 2D-Dev] [11] RFR [JDK-6686236] GIF native IIOMetadata assumes characterCellWidth/Height as 2bytes

[Prahalad Kumar Narayanan]

Hello Everyone

Good day to you.

Request your time in reviewing a simple fix for
    . Bug : [JDK-6686236]  https://bugs.openjdk.java.net/browse/JDK-6686236
    . Title : GIF native IIOMetadata assumes characterCellWidth/Height as 2bytes

Root Cause:
    . As per the gif image format specification (v89a), Character Cell Width and Character Cell Height values in Plain Text Extension block occupy 1 Byte each.
    . However, the GIFImageMetadataFormat and GIFWritableImageMetadata allow values in range [1, 65535] for the above attributes.
    . Note: Luckily, The bug does not affect GIFImageWriter because it writes only a single byte to the output stream. Thus ignoring the 3 higher order bytes in the "int" variables used for the two attributes.

Information on Fix:
    . The max permissible value is now restricted to 255 in both GIFImageMetadataFormat and GIFWritableImageMetadata. 
    . In addition, the html documentation describing GIF Image Metadata has been modified.
    . The attached test case verifies changes taken up in both metadata and metadata format.

Kindly review the change at your convenience.
Link: http://cr.openjdk.java.net/~pnarayanan/6686236/webrev.00/

Thank you for your time
Have a good day

Prahalad N.