This bug:
http://bugzilla.gnome.org/show_bug.cgi?id=132145
Was present in the Bugzilla for a long time now. It was reported because the
Frosty Logo script did not render correctly. Kevin Cozens discovered it was
due to the Sparkle Plug-in. Eventually, I decided to resolve it. I did that
by comparing the code (portion by portion and line by line) to the code in
GIMP 1.2. As a result of this process, I found four regression bugs[1] that
were fixed in this patch:
http://bugzilla.gnome.org/attachment.cgi?id=35345&action=view
However, there were still problems apparent. I temporarily hacked the code to
settle both plug-ins on the same identical pseudo-random number generator,
with the same seed, and compared the results. They were very different.
So I decided to add traces in the code to see where they were different. As I
went to add some traces, I discovered another regression bug, very similar to
another one I discovered previously, which I fixed. This seems to have
corrected the problem altogether, but the results were still not identical.
I added more traces, enough to cause both dumps to become a 1.5 GB (no typo
here) file, and then I discovered that a parameter passed to a function was
different in the plug-ins. I found out that it was a bug, because the 4th
byte (possibly alpha) of a color was not initialized. This bug was still
present in gimp 1.2.x. I fixed this bug too, and afterwards the results were
identical.
The patch with both of the newer fixes is this:
http://bugzilla.gnome.org/attachment.cgi?id=35501&action=view
In any case, I still noticed a problem. In the upper part of the image, the
shadows had completely horizontal edges. I noticed that this problem still
existed in GIMP 1.0.x (!), but it was still disturbing. After a lot of
investigation, and trying to reduce the script to a minimum that still
exhibits this problem, I found out the problem was because:
<<<
I discovered that the problem with the shadow was due to the fact that the
shadow was generated within the image boundaries and then the shadow layer was
moved (= translated) by an offset which caused it to have horizontal edges at
the top of the resultant image.
I prepared a patch to fix it. Sven told me to commit it to the CVS, which I
did. I forgot to commit it to the GIMP 2.2 branch, which Sven was gracious
enough to do late last night.
So now the sparkle plug-in is hopefully fully bug-free, and the Frosty logo is
back in action. Happy sparkling!
Regards,
Shlomi Fish
[1] - Well, one of them was just a swapped order for fetching two consecutive
random numbers from the random number generator, but that was revised too.
---------------------------------------------------------------------
Shlomi Fish shlomif@iglu.org.il
Homepage: http://www.shlomifish.org/
Knuth is not God! It took him two days to build the Roman Empire.
