Re: [Enigma-devel] Re: Thief stone

[Tacvek]

----- Original Message ----- 
From: "Ronald Lamprecht"

> Hi,
>
> Tacvek wrote:
> > > Oh, I think you misunderstood us: Enigma is running flawlessly,
> > > but the Microsoft(c) Image(c) Previewer(c) is buggy (or incomplete).
> > > Some other picture viewers, too; I think Irfan View has the same
> > > problem...
> > > Just try to open thief-template or some of the new shadows (sh-pull?)
> > > under Windows(c).
> >
> > Well actually it would affect any application that uses Window's PNG 
> > renderer.
>
> Only XP seems to be affected. W2K does not show any problems.

Interesting.


> As I just created new Icons with Gimp 2.2.8 that did not show any problems 
> I reloaded the affected images with this Gimp version and saved them 
> again. The resulting images do not show the Windows problems.

hmmm... that is good. It is still probably a good idea to run them through 
pngcrush or optipng, as the other images have been. This would have minimal 
impact on the size of the zip's or tarballs, but would slightly reduce the 
file size on disk.

As for the cause of the problem: My current guess is that the images are 
using the ability to apply a different filter to each scanline, which I 
assume is a relatively uncommonly used feature. Incorrectly implementing 
that could definately cause the image to appear to go random, and is a bug 
that is easy to miss. optipng and pngcrush appear to only generate images 
that use the same filter for all scanlines, which would explain why they are 
able to fix the problem.

However, that is only a guess, and there is a pretty good chance I am wrong. 
Anyway, this is getting offtopic, so I shall stop.