Miscellaneous stream improvements

[jlstevens]

This PR aims to implement the suggestions in issue #1426.

The first commit distinguishes SingleTap from Tap and DoubleTap where Tap is supposed to capture all tap events.

@bryevdv Unfortunately I can't quite implement the intended semantics for Tap as a double tap event should resolve into two taps. As far as I can tell, the way hammer is used in bokeh does not allow for this.

Is this correct? Would it be reasonable to add a bokeh event that reflects all taps, whether single or part of a double tap?

[jlstevens]

Here is an example (including all the code!) of a little visualization using the new Draw stream:

[jlstevens]

Note that even after having updated the skip conditions, odd things happen when using %%opts Path [toolbar=None] in the example shown above. Needs investigating.

[jbednar]

Looks super useful, thanks! Is the three-pronged "if" statement needed because a Curve cannot be empty? Avoiding tricky logic like that seems like a good reason to allow empty Curves...

[philippjfr]

Is the three-pronged "if" statement needed because a Curve cannot be empty?

I think in this case it's to start a new curve every time a new drag even is started. That said in most cases we do support empty Elements, e.g. you can do hv.Curve([]).

[jlstevens]

I think in this case it's to start a new curve every time a new drag even is started.

That's right! If you can suggest a way to shorten the example, I would be very happy to try it out.

[jlstevens]

Anyway, in my last commit I added the JS to clip the x,y values to the axis ranges for PointerXY. The JS is pretty horrible so I want to clean it up before this PR is merged. Otherwise, I have implemented all the proposal I made in the issue.

[philippjfr]

The JS is pretty horrible so I want to clean it up before this PR is merged.

It's not pretty but I'm not sure how it can be improved.

[jlstevens]

It's not pretty but I'm not sure how it can be improved.

If nothing else, I can improve the formatting. After that, I think this PR is ready to merge though it might be worth investigating the odd behavior when toolbar=None...

[jlstevens]

To make it easier to test, here is the text of the gif example above:

from holoviews.streams import Draw
vals, curves = [], {}

def callback(x,y, stroke_count):
    global vals, curves
    curve = hv.Curve(vals)
    if len(curves)==0:
        curves[stroke_count] = hv.Curve([(x,y)])
    elif stroke_count != (len(curves)-1):
        curves[stroke_count]= curve
        vals = []
    else:
        vals.append((x,y))
        curves[stroke_count]= curve

    return hv.Path([curve.data for curve in curves.values()])

hv.DynamicMap(callback, streams=[Draw(x=0,y=0)])

It is also worth noting that we decided to call the future stream used for actually dragging a glyph/element around (i.e drag + selection) Drag.

[jlstevens]

@philippjfr Other than the odd behavior with toolbar=None (which I don't know what to make of) I think this PR is ready for review.

[philippjfr]

Should I go ahead and merge? Toolbar option is fixed in #1442.

[jlstevens]

Should I go ahead and merge?

Given that the toolbar issue is fixed, yes please!