Re: [Gimp-developer] I am hoping to contribute to GIMP. I have some ideas, but I want input if possible.

[Jehan Pagès <jehan marmottard gmail com>]

Hi,

On Tue, Nov 12, 2013 at 5:30 PM, DeVonte Applewhite <dapplewh nd edu> wrote:
> Hello all,
>
> I am in a Data Structures class which has a final project. This project
> requires students to fix bugs, improve preexisting data structures, or add
> extra features to an open source project that has an active community. My
> group chose GIMP.

Nice choice! :-)

> I have some ideas about changing data structures in hopes
> of generalizing some implementations, improving execution speed and
> reducing the amount of code needed to complete implementation of the .h
> files.
>
> Here are 3 of our ideas. If you could give input (feasibility, faults in
> our plan of action, predicted improvements upon success of these ideas,
> suggestions) on any or all of our ideas, that would be greatly appreciated.

Well I won't comment all the ideas in detail, and my guess is there
are few chances others will either, because that would take quite a
time! We don't know the whole code by heart, so to understand what you
speak about, we would have to read the code you speak about carefully;
and even so, when I see the kind of changes you propose, I'm not sure
we will just say that's good ideas out of our head by just reading
code. You seem to be proposing mostly API change or code optimization.
But as often in optimization, it starts with gut feeling (except when
dealing with obvious bad designs), and some algorithm cost
computation, but in the end only real testing will really tell.
So if you really feel that's the way to go, you can still implement
it, test it, and if it appears to be a lot better than previously,
then you won. Propose a patch with some benchmark results and someone
will have at look at this.

Now this said, I really wonder if API changes or algorithm
optimizations are the best way to start in OpenSource contribution. A
codebase like GIMP is huge and very complicated and you want to start
with base classes. First of all, classes which are used in a lot of
places may also break many different pieces of code if you change
things (API or algorithm) there. So that implies a lot of regression
testing, which means a lot of time.
Second, even though base classes are indeed used in a lot of places,
and optimizations are always good, well it is not that obvious that
the optimization will get that tremendous speed improvements compared
to all the other things done along the way.
Last, API change just for the sake of API change, I'm not sure that's
the best idea. We will usually do something because we actually want
to use it and see it will make actual code better. I'm not sure if API
change which "may" make some future code better is a good way to do
it.

I would think an easier way to start contributing is to fix bugs. We
have quite a lot of bugs in our bug tracker waiting to be fixed. Just
pick some of them, and fix them. Then you are sure this will be wanted
code, and there is no "maybe" or incertitude. Also that's a lot
easier, though very visible.

But if you're sure your propositions are worth it, the best is to do
the changes and propose patches. :-) As I said, I haven't looked at
them in details. Maybe that's great ideas, no idea. I know some
contributors start with base consolidations, not fixes. It happens.
In any case, have fun with GIMP,

Jehan

> 1. gimp/libgimpmath/gimpmathtypes.h (file in
> question:gimp/libgimpmath/gimpmatrix.h(c))
> This file declares math structures that gimp uses like vectors and
> matrices. The GimpMatrix structure come in 2X2, 3X3 and even 4X4 versions.
> Each matrix is a 2Dimensional gdouble array with the appropriate amount of
> elements to span the NXN matrix.I believe this data structure is used for
> computation during image editing. There are functions handling
> comparisons, identities, transformations, rotations, translations and
> various other
> matrix operations. Possible changes: I believe the declaration of 3 special
> kinds of gimp
> matrices can be generalized to a struct (or class) that holds and defines
> an NXN matrix. We
> could make it as general as possible to save the amount of code necessary
> to complete the tasks. This also eliminates two extra structs in the .h
> file. We could also change the structure that holds the matrix elements.
> One way could be by making a nested linked list to emulate an NXN matrix.
> This way, we keep everything in memory and not on the stack. If necessary,
> we could even overload the [] operator to make the functionality act like
> an array. We could also use the std::vector<T> data structures included in
> the <vector> library to allow for pushing and popping of matrix data
> structures to make them dynamic and or more fail-safe.
>
> 2. gimp/app/core/gimpcontainer.h
> This class contains a data structure that is used to store different things
> about the
> various objects in gimp. It works hand and hand with the GimpObject class.
> This
> class uses what I believe to be some form of tree or heap structure. The
> class
> refers to add, remove, reorder, and getChild functions that are defined
> across the
> class. The gimp.h code uses the GimpContainer class pointers for everything
> from fonts, to documents, to displays. As this data structure is used with
> GimpObject (which controls a large amount of functionality in gimp) and is
> heavily
> referenced in the gimp.h file, optimizing this class could go a long way in
> optimizing the code. If we decrease the amount of time to “reorder” the
> tree, then
> we decrease the amount of time several other objects take to be initialized
> and
> added to the tree.
>
> 3. gimp/libgimpmath/gimpvector.h(c)
> The GimpVector data structure keeps track of axis orientations and lengths.
> I believe this is used in the various drawing tools. I also believe the
> automated shapes functions may use it for drawing polygons. The vector data
> structure is a structure that holds four gdouble variables that are
> separately declared (gdouble x, y, z, w for the 4axis vector for example).
> There are three
> versions of the gimp vector: 2axis, 3axis, and 4axis. A potential change to
> GimpVector could be altering the way that it is stored like we plan to
> change the GimpMatrix. This means making a
> streamlined generalized vector that can be of dimension N. Storing the axes
> in an std::vector<T> or a linked list of size N could generalize the vector
> to be declared of any arbitrary number of axes. Another thing we could do
> is overload the operators between vectors such as addition, subtraction and
> multiplication. Currently they are of the form, GimpVector add(GimpVector
> &gv1,GimpVector &gv2). We could make it as easy as adding two vectors with
> the + operator to make the code more readable. We can also overload various
> other operators to make the GimpVector data structure more flexible and
> powerful. This hopefully will increase the functionality and potency of the
> GimpVector data structures and make them more accessible to new Gimp
> developers in the future.
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