I would advocate for calling yours something different. path.Path is really a container for a Bezier curve and is probably best left as simple as possible. There is probably an interesting discussion about right is-a and has-a relations between Path, FancyPath (don’t use that name!), and FancyArrow (which I do not have a clear view of yet).
Tom
···
On Fri, May 15, 2015 at 10:53 AM, Thomas Caswell <tcaswell@…149…> wrote:
A few very quick comments (just skimmed the docstrings)
We already have a mpl.path.Path class, please don’t shadow that.
I read the Path class and based mine on that. The problem is that I want to be able to place nodes along the path (like labels) and so I need to ask it questions. Maybe we should just extend the existing Path class? Or else we should call my Path something different?
Is your
Pathgoing to be anArtistthat is responsible for drawing it’s self or does in serve a role like the existingPathin that it is used by other artists as part of theirdraw?
This feels very similar to the
FancyArrow(with classes being passed in to control how the arrow is styled), would this make sense as an extension to that code? This does seem more general, maybe it makes sense to start from scratch and implementFancyArrowin terms of this code.
Yes! Didn’t know about that. I think modifying and extending that code might be a good way forward.
Tom
On Fri, May 15, 2015 at 10:40 AM Neil Girdhar <mistersheik@…149…> wrote:
I have a draft proposal of the long term goal for what an interface could look like for drawing arrows between coordinates or nodes. I based the design on the tikz manual (http://pgf.sourceforge.net/pgf_CVS.pdf), so it might help to flip through that to get an idea for the basis of this design. I tried to separate the creating of Path objects with the drawing of paths since it’s often really useful when compositing layouts to be able to do math with with the positions of things before drawing anything. For example, when automatically positioning nodes.
I’m not committed to this design; it’s just an outline to get feedback.
Best,
Neil
class Axes_(_AxesBase):
def path(self, path, draw=True, fill=False):
“”"
If draw is not falsy, draws along the path using the draw
specification.
If fill is not falsy, fills the closed path using the fill
specification.
Parameters
path is a Path object or path commands with which to create one.
draw is a draw specification:
either the value True, which indicates some defaults, or else
False, or else a dictionary with the following keys:
color
opacity
line_width
line_join
begin_tip is a Tip object
tip or end_tip is a Tip object
dashed is a dash specification
a dash specification
either dictionary containing:
dash_pattern
an iterable of numbers specifying the length of the dashes
and gaps in points. E.g., [2, 3, 4, 3] means on for 2
points, off for 3, on for 4, off for 3, i.e., dash-dotted.
dash_phase
Shifts the start of the dash pattern by dash_phase points.
or a string, one of:
‘solid’
‘dotted’, ‘densely dotted’, ‘loosely dotted’
‘dashed’, ‘densely dashed’, ‘loosely dashed’
‘dash dot’, ‘densely dash dot’, ‘loosely dash dot’
‘dash dot dot’, ‘densely dash dot dot’, ‘loosely dash dot dot’
fill is a fill specification:
TODO
“”"
class Path:
def init(self, path_commands):
“”"
path_commands is either
a coordinate (representing a move to in the first position, or a
line to in any other position)
MoveTo(coordinate)
LineTo(coordinate_or_node, draw=None)
CurveTo(coordinate_or_node, control_points, draw=None)
ClosePolygon()
optional draw commands override the draw specification of the whole
path within that edge.
a coordinate is either an (x, y) pair, or a Coordinate object.
a node is a Node object.
“”"
def at_position(self, fraction=0.5):
“”"
Returns a coordinate fraction of the way along the line.
fraction can be one of ‘at end’, ‘very near end’, ‘near end’,
‘midway’, ‘near start’, ‘very near start’, ‘at start’
“”"
def node_at(node, fraction=0.5, location, …)
“”"
Sets the node’s position so that it sits flush to the path.
Parameters
location :
Could be ‘above’, ‘below’, ‘on’, or a number, which is the number
of points away from the path to place the node.
“”"
def pin_node(node, pin_distance, draw=draw_specification):
pass
class Coordinate:
@property
def coordinate(self):
return (self.x, self.y)
def node_at(self, node, angle):
“”"
Places the node so that it is in the direction angle from the
coordinate. E.g.,
angle=pi/2, or angle=‘above’ places the node so that the coordinate is
touching the center-bottom of the node.
angle could be ‘above’, ‘below’, ‘left’, ‘right’, ‘above left’, etc.
“”"
class Node:
“”"
Available Node objects:
Rectangle, Circle
“”"
@property
def center(self):
return (self.x, self.y)
def node_at(self, node, angle):
“”"
Places the node so that it is in the direction angle from the
coordinate. The node could be an arrowhead for example.
“”"
def convex_hulls(self):
“”"
Returns a list of convex hulls. The convex hulls are used when
position one node or arrowhead flush with another using the
separating axis algorithm.
“”"
class Tip:
“”"
Available Tip objects:
ButtCap (no tip, the default)
RectangleCap, TriangleCap, RoundCap
ArcBarb, Bar, Bracket, Hooks, Parenthesis,
StraightBarb, TeeBarb
Circle, Diamond, Ellipse, Kite, Arrow,
Rectangle, Square, Stealth, Triangle,
TurnedSquare
TipCombination (accepts multiple tips and merges them)
“”"
def init(self, draw=None, fill=True, reversed_=False):
pass
def convex_hulls(self, line_width):
“”"
Returns a list of convex hulls for use with placement
whereby the arrow faces right starting at the origin.
“”"
def transmute(self, line_width):
“”"
Returns a pair of lists (draw_path, fill_path).
“”"
@property
def draw_specification(self):
“”"
is a draw specification, or None to use the parent line’s
“”"
def fill_specification(self):
“”"
Is a fill specification, or True to use defaults based
on the parent line’s draw color, or False to use an open fill.
“”"
Usage:
draw an arrow from point to point.
ax.path([(x, y), (x2, y2)], draw={‘tip’: Arrow()})
Create a path.
p = Path([(x, y), (x2, y2)])
Create a node along the path.
n = p.node_at(Label(“some label”))
Draw the path using an arrow, and the node.
ax.path(p, draw={‘tip’: Arrow()})
ax.node(n)
On Wed, May 13, 2015 at 11:27 PM, Thomas Caswell <tcaswell@…149…> wrote:
Sorry, I may have been being a bit dramatic
In mpl.patches: Arrow, FancyArrow, YAArrow, FancyArrowPatch, ConnectionPatch + annotation related artists + some classes in axisartist which now that I look at them are not really general purpose arrow tools. I had not been counting quiver (or barbs) or sankey.
Neil: Those are all great questions! Much of the arrow related code was written by Joe-Joon Lee who (by having read a good deal of his code) has a habit of writing very power but very opaque python.
I believe that the line join style is controlled by
joinstyleon the graphics context and it is up to the backends to implement that correctly.
Tom
On Wed, May 13, 2015 at 10:58 PM Neil Girdhar <mistersheik@…149…> wrote:
Okay, I’m looking at this in more detail and there may be some design concerns:
The arrow placement is decided without asking the arrow any questions, such as its bounding box. Instead, the arrow should return a bounding box and then the line should retreat until the bounding box no longer intersects the target node. Then the arrow should be placed. This doesn’t matter so much when you have a simple arrow like this: ---->, but it’s a big deal when you have an arrow like ----| . In this case, the sides of the arrow risk intersecting with the target node.
I’m not keen on implementing every arrow three times: <-, ->, <->. This really should be handled by the code placing the arrows for many reasons:
- It should also be possible to have a different arrowhead at either end of the line.
- It should be possible to stack the arrows, for example having two heads one after another (to represent two kinds of relationships). This is another reason to be able to ask the arrowhead its length and so on.
I don’t understand the “monolithic” keyword. How can the arrow draw the line as well when it doesn’t know the line style, color and so on?
I think I like the design of the transmute function. I’m curious: ultimately, where does the mutation_size come from? Is it a global scale applied to the figure, or is it based on the linewidth, or?
When you emit a set of lines, how are they joined? If I draw a line having linewidth 0.1 from the origin to (1, 0), and back to (0, 0.5), what happens at the tip? Are two rectangles drawn (each having width 0.1, but oriented differently)? Is a bevel created? A miter? Or is the tip rounded? Can this be controlled? See page 166 of the manual I sent earlier (search for tikz/line join).
Best,
Neil
On Wed, May 13, 2015 at 10:14 PM, Neil Girdhar <mistersheik@…149…> wrote:
Thanks, it works!
I needed to add:
import matplotlib.patches
to one file and
plt.show()
to the other.
Any word on the locations in the code of the seven arrow drawing methods?
I’ve located the arrow drawing code in tikz, and so I can start porting it over. I’m curious, do we know the linewidth of the edge being decorated by the arrow? To make arrows scale nicely, most of the arrow dimensions are given in two pieces: an absolute value (in points for example) and a line width factor. The dimension is the absolute value plus the line width factor times the line width. The TikZ manual explains: “This makes it easy to vary the size of an arrow tip in accordance with the line width – usually a very good idea since thicker lines will need thicker arrow tips.”
Best,
Neil
On Wed, May 13, 2015 at 10:07 PM, Benjamin Reedlunn <breedlun@…149…> wrote:
Neil,
I have attached code to draw the arrowhead.
-Ben
On May 13, 2015, at 7:44 PM, Neil Girdhar <mistersheik@…149…> wrote:
Do you have the code that you used to draw the arrowhead? I’m up to date now on the development workflow (http://matplotlib.org/devel/gitwash/development_workflow.html), so I’m ready to start working.
Thanks,
Neil
On Wed, May 13, 2015 at 9:10 PM, Benjamin Reedlunn <breedlun@…149…> wrote:
Yes, I fully agree that we need to unify the many different ways to draw arrows.
Neil, in case an example would be helpful for you, I have attached a module that includes a custom arrowhead class. The arrowhead class works with the with the ax.annotate() method. (I like the annotate method because it allows me to easily mix and match coordinate systems for arrow placement.) As you can see in the attached pdf, the custom arrowhead doesn’t include fancy Bezier curves, but that could be added.
-Ben
On May 13, 2015, at 2:54 PM, Thomas Caswell <tcaswell@…149…> wrote:
The other thing that should be done is to unify the (I think 7?!?) unique ways to draw arrows in mpl.
On Wed, May 13, 2015 at 4:52 PM Neil Girdhar <mistersheik@…149…> wrote:
Yes, I just noticed that as well. That’s how the tikz pgf code looks (a sequence of line_to and curve_to commands and so on) so it should be easy to port over the various shapes.
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On Wed, May 13, 2015 at 4:49 PM, Eric Firing <efiring@…229…> wrote:
On 2015/05/13 10:12 AM, Neil Girdhar wrote:
If you want to make arrowheads look at all decent, they really need to
be enclosed in Bezier curves. See the diagram here:Mpl paths support Bezier curves.
http://matplotlib.org/api/path_api.html?highlight=bezierThe first two look like garbage. The last one is the only one that
looks good imho.That depends on the application, and the observer.
Sure, but I may as well port them all of the tikz arrowheads over since most of the work would be figuring out how to do it.
Eric
Best,
Neil
On Wed, May 13, 2015 at 4:09 PM, Eric Firing <efiring@…229…
mailto:efiring@...229...> wrote:On 2015/05/13 9:36 AM, Neil Girdhar wrote: I don't know matplotlib well enough (yet) to know what the change would consist of. I suggest you take a look at the beautiful tikz manual: [http://pgf.sourceforge.net/pgf_CVS.pdf](http://pgf.sourceforge.net/pgf_CVS.pdf) Very helpful, thank you. The arrows.meta on page 201–212 are really well-designed and beautiful. Compare this with matplotlib's custom arrows: [http://stackoverflow.com/questions/16968007/custom-arrow-style-for-matplotlib-pyplot-annotate](http://stackoverflow.com/questions/16968007/custom-arrow-style-for-matplotlib-pyplot-annotate) How do I make tikz's arrowheads available for all backends? My guess offhand is that this is a matter of using the mpl API. I don't think we would want to add all of these types and options to the mpl core; but a toolkit might be ideal for this. The mpl API, which generates the same results for all backends, is quite complete and flexible. Things like arrowheads are Patch objects, and you can specify any path you want. The main trick is figuring out how to handle transforms--what kind of coordinates should the path be specifying? How should things scale as a figure is reshaped and resized? For many of these types you could also use mpl Line2D objects, for which several properties including cap style can be specified. Not all of the TikZ options would be available, but perhaps enough. Eric
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