xournal-devel

[Xournal-devel] Arrow Tool / Getting into development

[Homo F. <gor...@gm...>]

Hi,

I just got around to building xournal-next on Windows and would like to add
a few tools (not using the shape recognizer, as i want more control over
size and position), although I can't seem to understand the source code all
that well. For guidance I looked at code which defines the ruler paths in
xo_paint.c in the following functions:

- void create_new_stroke(GdkEvent *event)
- void continue_stroke(GdkEvent *event)
- void finalize_stroke(void)

Now my idea is to add new points to that path, so I can add an arrow head
after the straight line (like this: ----|>) . Where would one insert these
points? In xo_shapes.c make_circle_shape() adds points to the
ui.cur_path.coords array, but I can't seem to get it to work this way.

I'd be grateful for any guidance in this direction.

Also, it took me quite some time getting Xournal and gtk2 to build on
Windows (using MSYS2 / mingw64). If anyone is interested, I posted updated
instructions in the SourceForge forum

Thanks,

Mo.

Re: [Xournal-devel] Arrow Tool / Getting into development

[Denis A. <au...@ma...>]

Hi there,

Just adding points to ui.cur_path.coords (and adjusting num_points) is 
not necessarily enough, because that is just a temporary points array 
used while drawing -- at the end of the process, ui.cur_path will 
eventually get inserted into the page and drawn.  For regular drawing, 
create_new_stroke() allocates ui.cur_item and fills some of the data; 
continue_stroke() updates ui.cur_path and draws segments as the pen is 
being moved; and finalize_stroke() takes care of finishing the job: 
cleans up the data in ui.cur_path, copies it into ui.cur_item->path, 
updates the gnome canvas structures, and adds ui.cur_item onto 
ui.cur_layer->items to make it part of the page's data structures.

You won't need to do all these things yourself, but you do need to make 
sure that the place where you modify ui.cur_path's contents is before 
the moment where it gets copied into data structures that will remain in 
place in the journal.

Easy case: If your arrow is going to be part of the same polyline as the 
stroke is goes onto, i.e. the stroke + arrow are all a single connected 
polygonal shape, then you can indeed insert it at the beginning of 
finalize_stroke() (updating ui.cur_path.coords and num_points) and the 
code will take care of it.

Hard case: If the arrow is its own separate polyline, then it will 
become a distinct item both in gnomecanvas (for display) and in 
ui.cur_layer (for data storage), so you need to make sure those get 
created, and that the creation operation can be undone. The best place 
to look for such things is indeed the shape recognizer.

In xo-shapes.c, try_arrow() will take existing strokes and create 
several strokes, if you look at the end of the code for try_arrow(), we 
create several stroke items by hand. The fastest way to do it is just 
the same as the way the arrow head is created at the end of try_arrow():

   realloc_cur_path(3);
   ui.cur_path.num_points = 3;
   ui.cur_path.coords[0] = x2 - dist*cos(angle+delta);
   ui.cur_path.coords[1] = y2 - dist*sin(angle+delta);
   ui.cur_path.coords[2] = x2;
   ui.cur_path.coords[3] = y2;
   ui.cur_path.coords[4] = x2 - dist*cos(angle-delta);
   ui.cur_path.coords[5] = y2 - dist*sin(angle-delta);
   insert_recognized_curpath();

We make sure cur_path is large enough for 3 points, fill in the 
coordinates, and then insert the new curpath into the journal.

*However* you can't use insert_recognized_curpath() as is, because it 
assumes that a recognizer operation is in progress and the undo stack 
contains an "ITEM_RECOGNIZER" entry, with a list of erasures already in 
place. (See the first 6 lines of code in remove_recognized_strokes(), 
which gets called before any call to insert_recognized_curpath(): we 
create a new undo item).

You can either piggyback on this, making your arrows in a "recognizer" 
undo operation (this has implications for the undo process, it'll undo 
in two stages) but with no erasures if you are not removing any 
user-drawn stroke to replace it with the arrow, and calling 
insert_recognized_curpath();  or make a different function similar to 
insert_recognized_curpath() but that doesn't place information into the 
undo stack in this particular way (instead makes an ITEM_STROKE undo 
operation).

Sorry if this is technical, but that is not the easiest part of the code 
to modify if you want to create an extra polyline along the way -- 
easiest if you just make the arrowhead part of the same continuously 
drawn polyline as the stroke, in that case just add your arrow points to 
ui.cur_path at the beginning of finalize_stroke() (before cur_path gets 
copied into other data structures and redrawn on screen).

Denis

On 01/28/2017 07:22 AM, Homo Fürst wrote:
> Hi,
>
> I just got around to building xournal-next on Windows and would like to
> add a few tools (not using the shape recognizer, as i want more control
> over size and position), although I can't seem to understand the source
> code all that well. For guidance I looked at code which defines the
> ruler paths in xo_paint.c in the following functions:
>
> - void create_new_stroke(GdkEvent *event)
> - void continue_stroke(GdkEvent *event)
> - void finalize_stroke(void)
>
> Now my idea is to add new points to that path, so I can add an arrow
> head after the straight line (like this: ----|>) . Where would one
> insert these points? In xo_shapes.c make_circle_shape() adds points to
> the ui.cur_path.coords array, but I can't seem to get it to work this way.
>
> I'd be grateful for any guidance in this direction.
>
> Also, it took me quite some time getting Xournal and gtk2 to build on
> Windows (using MSYS2 / mingw64). If anyone is interested, I posted
> updated instructions in the SourceForge forum
>
> Thanks,
>
> Mo.
>
>
> ------------------------------------------------------------------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, SlashDot.org! http://sdm.link/slashdot
>
>
>
> _______________________________________________
> Xournal-devel mailing list
> Xou...@li...
> https://lists.sourceforge.net/lists/listinfo/xournal-devel
>

-- 
Denis Auroux
UC Berkeley, Department of Mathematics
817 Evans Hall, Berkeley CA 94720-3840, USA
au...@ma...

[Xournal-devel] Fwd: Arrow Tool / Getting into development

[Hans R. <gor...@gm...>]

Hi,

thanks for your very in depth answer. I just got to try this two days ago
and got it working!. I've added a few more points to the existing polyline
inside continue_stroke() to create an arrow head. Now I wanted to switch
between the ordinary ruler and my modified one. This was quite a hurdle and
certainly isn't nice looking code. I didn't want to create a new tool from
scratch, as that would have taken a lot longer. Instead I added a new int
to the UIData struct, that serves as a switch for the different "ruler
tools". This int can be modified by a GtkMenuToolButton in the toolbar,
which has multiple radio items (the button itself does nothing). All these
items are connected to the same handler and by comparing the sender's label
to strings the int value gets set (What could possibly go wrong? Well
translation is an issue for sure. I think there is a possibility to send
this data over the gpointer user_data, but I didn't try that one). With
this information I can select the tool that will be applied
inside continue_stroke(). Currently the UI looks like this (i don't know if
embedded pictures will work here):

[image: Inline-Bild 1]
[image: Inline-Bild 2]
Its not really clean and forward, but I have to leave it at that for now.
Changing the ruler toggle button into a radio control required changing
code in parts of Xournal that caused a myriad of new problems. I didn't
want to face those without a debugger.
Maybe you have a better idea on how to handle all this. As it is now, I'm
quite happy as these were my most wanted features.

Thanks again,

Mo.

Re: [Xournal-devel] Fwd: Arrow Tool / Getting into development

[dmg <dm...@tu...>]

Hi Hans,

thank you for trying this. Is there a place where we can download the
patches?

thank you!

--dmg

On Fri, Mar 17, 2017 at 2:25 PM, Hans Rochus <gor...@gm...>
wrote:

> Hi,
>
> thanks for your very in depth answer. I just got to try this two days ago
> and got it working!. I've added a few more points to the existing polyline
> inside continue_stroke() to create an arrow head. Now I wanted to switch
> between the ordinary ruler and my modified one. This was quite a hurdle and
> certainly isn't nice looking code. I didn't want to create a new tool from
> scratch, as that would have taken a lot longer. Instead I added a new int
> to the UIData struct, that serves as a switch for the different "ruler
> tools". This int can be modified by a GtkMenuToolButton in the toolbar,
> which has multiple radio items (the button itself does nothing). All these
> items are connected to the same handler and by comparing the sender's label
> to strings the int value gets set (What could possibly go wrong? Well
> translation is an issue for sure. I think there is a possibility to send
> this data over the gpointer user_data, but I didn't try that one). With
> this information I can select the tool that will be applied
> inside continue_stroke(). Currently the UI looks like this (i don't know if
> embedded pictures will work here):
>
> [image: Inline-Bild 1]
> [image: Inline-Bild 2]
> Its not really clean and forward, but I have to leave it at that for now.
> Changing the ruler toggle button into a radio control required changing
> code in parts of Xournal that caused a myriad of new problems. I didn't
> want to face those without a debugger.
> Maybe you have a better idea on how to handle all this. As it is now, I'm
> quite happy as these were my most wanted features.
>
> Thanks again,
>
> Mo.
>
> ------------------------------------------------------------
> ------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> _______________________________________________
> Xournal-devel mailing list
> Xou...@li...
> https://lists.sourceforge.net/lists/listinfo/xournal-devel
>
>


-- 
--dmg

---
Daniel M. German
http://turingmachine.org