[Gimp-developer] Questions on GIMPs technical architecture

[scl <scl gplus gmail com>]

Hi,

while getting into deeper touch with GIMPs code I also dealt with
its software architecture. For this I analyzed and visualized the
#include-dependencies with the Doxygen tool [1]. You can see the
results at my blog [2].

The following questions arise to me:
1. The diagram show obvious circular dependencies between some 
components (marked in red and noted textually). There are also more 
circular dependencies within some components. Also in the code, like in
/app/tests I found hints on circular dependencies, but it was worked
around them instead of solving them.
Such circular dependencies make it hard to test or substitute single
components, introduce undesired side effects and thus make the code
harder to maintain, see also [3].
I think all could be benefit from a clearer code. How it could look,
shows the GEGL example [2].
I respect the hard maintaining work that has been done yet and don't 
want to lecture anybody, so I just ask:
- Are they in the code by intention?
- If not, are there objections against removing them?

2. The directories /devel-docs and /tools both contain developer tools.
If we had them together in the /tools directory and the /devel-docs
directory only contained only documents, the architecture would be
easier to understand, because one component in the diagram would be dropped.

3. Both modules and plug-ins provide optional functionality and
can be de-/activated dynamically at runtime. With a few exceptions
they use the same libgimp* libraries.
Why is there a distinction between modules and plug-ins?
Can we simplify the architecture and the UI by removing this distinction
and handle them the same?

4. What exactly is the Wire protocol and how does it work?
I already read, that it is a transparent, not threadsafe,
shared memory for communication between the GIMP core and the plug-ins.
But that's all I found yet and it doesn't give me enough understanding
of the protocol.

5. Why does only thee /apps directory contain (unit) tests and not the 
whole application? Are there objections against having such tests
in the other parts of GIMP?

6. Which considerations played a role in the past for the architecture,
like optimization for performance, maintainability etc.?

7. Who else here cared or cares about such questions?

As we all developers could benefit from clarifying these questions,
I'd be glad about your answers, even if they answer only a few 
questions. When we have something for the real, I could take it to the 
wiki and/or /devel-docs directory.

Thank you in advance.

Sven


[1] http://www.stack.nl/~dimitri/doxygen/
[2] 
http://sclaussner.blogspot.de/2013/06/some-already-noticed-it-im-active-in.html
[3] 
http://stackoverflow.com/questions/1897537/why-are-circular-references-considered-harmful