[Bf-committers] Learning Blender Code?

[John Alway]

Thanks to everyone for the excellent feedback.

Thanks, Jonathan for the details on nurbs.   I definitely don't want to
step on any toes.  I was just looking for a way to get started and thanks
for the green light!

Regards,
...John


On Wed, Jul 2, 2014 at 11:39 AM, Jonathan deWerd <jjoonathan at gmail.com>
wrote:

> >> So, I'm wondering how others have learned the code, or is it just a
> matter
> >> of putting in lots of time?
>
> It's just a matter of putting in lots of time. Not what you wanted to hear
> but I think you suspected it was true already.
>
> I'm the summer student working on NURBS. Just wanted to drop by and say
> that you could work on this bug without stepping on my toes. The NURBS
> extrusion operator already exists, ctrl+click just doesn't call it. If you
> stick to calling the extrusion operator you will guarantee compatibility
> with any changes that I make since I have to make the extrusion operator
> work regardless.
>
> In order to decide which edge to extrude from, you will need to access the
> NURBS object (search for "typedef struct Nurb"). Relevant fields are:
>
> Nurb nb;
> nb->pntsu; //Number of control points in u direction
> nb->pntsv; //Number of control points in v direction
> nb->bp; //A 1D array of BPoints that holds the 2D array of control points.
> // Writing coords (u,v), they are packed like
> //
> (0,0),(1,0),...,(nb->pntsu-1,0),(0,1),(1,1),...(nb->pntsu-1,1),...,(nb->pntsu-1,nb->pntsv-1).
>
> BPoint p;
> p->vec[0]; // x
> p->vec[1]; // y
> p->vec[2]; // z
> p->vec[3]; // w
> // NOTE: this BPoint corresponds to the point (x, y, z) in space, *not*
> (x/w, y/w, z/w) as per mathematical convention for homogeneous coordinates.
>
> Hope that helps. Nurb::bp packing order and BPoint's strange
> half-homogeneous behavior were discovered by trial+error+debugger. I
> haven't written any interactive operators yet so I can't help you there. I
> don't think you would be shooting yourself in the foot by working with the
> NURBS code. It's old but it seems to use the same operator and undo code as
> the rest of blender. It's also relatively monolithic compared to BMesh: it
> doesn't change representations in editmode, it doesn't keep its own
> separate stack of operators, it doesn't have a domain-specific language to
> represent modifications (why does BMesh even have that anyway?), and the
> relevant struct definitions fit handily on half of a single screen.
>
> Cheers,
> Jon
>
>
> On Jul 2, 2014, at 11:50 AM, Howard Trickey <howard.trickey at gmail.com>
> wrote:
>
> > Some introductory FAQ material is here:
> > http://wiki.blender.org/index.php/Dev:Doc/FAQ#Source_Code_FAQ
> >
> > As it says there, reading all of the docs on
> > http://wiki.blender.org/index.php/Dev:Source/Architecture
> > is useful, though hard-going and somewhat out of date.
> >
> > It's probably best to start on just a small area of the code and not
> worry
> > about the rest.
> > Follow through what happens when you execute some command in an area that
> > you are interested in.
> > Do what you are trying to do: fix a small problem or make a small feature
> > change in that command.
> > Probably doing a NURBS task isn't the best idea to start, since there is
> a
> > summer student right now working on revamping NURBS, and anyway that code
> > is fairly old and somewhat removed from the modern part of Blender.
> >
> > - Howard
> >
> >
> > On Wed, Jul 2, 2014 at 11:07 AM, John Alway <jalway at gmail.com> wrote:
> >
> >> Hello,
> >>
> >> I've been working to understand Blender code so that I can try my hand
> at
> >> fixing some bugs and adding some features as needed.   However, I'm
> finding
> >> the learning curve to be quite steep.   C and C++ code per se are no
> >> problem for me, but it's hard to determine what the code is doing,
> because
> >> there are many abstract concepts that have been implemented.
> >>
> >> I was trying my hand at Issue T39656, just to see what it would take:
> >> https://developer.blender.org/T39656
> >>
> >> And, to help me along, I've been using the Visual Studio debugger and
> I've
> >> read many things out of the wiki, including this overview:
> >>
> >> http://wiki.blender.org/index.php/Dev:Source/Architecture/Overview
> >>
> >> However, at the end of the day, this is proving to be pretty heavy
> going.
> >>
> >> So, I'm wondering how others have learned the code, or is it just a
> matter
> >> of putting in lots of time?
> >>
> >> I do know OpenGL and I have studied many graphical concepts, and I've
> done
> >> a lot of matrix math for rotating and translating objects, etc.   But,
> I'm
> >> sure there is much to more learn, anyway.  There always is!
> >>
> >> Anyway, I'm just looking for pointers and any kind of help on this.
> >>
> >> Thanks for any feedback!
> >> ...Regards,
> >> John
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