Update label for ColorBarWidget (which relies on ColorBarVisual)

[macrocosme]

Hi,

I'll start with that I really like vispy! I wonder if the following would be worth a pull request.

Using vispy 0.5.0.dev0, I was trying to update dynamically the colorbar label from ColorBarWidget.

(1) To set the label from the colorbar widget (ColorBarWidget), I need to pass the label_str directly as the 'label' parameter isn't linked to anything. This works well. This means that the call to ColorBarVisual in ColorBarWidget could be changed to

def __init__(self, cmap, orientation,
                 label="", clim=("", ""),
                 border_width=0.0, border_color="black", **kwargs):

        dummy_size = (1, 1)
        self._colorbar = ColorBarVisual(size=dummy_size, cmap=cmap,
                                        orientation=orientation,
                                        **label_str**=label, clim=clim,
                                        border_width=border_width,
                                        border_color=border_color, **kwargs)

(2) To update it I tried two things. First, I try to simply recreate (self.grid.remove_widget followed by self.grid.add_widget) the whole widget and add it back to the grid. E.g.

cbar = scene.ColorBarWidget(orientation=position,
                                    label_str=label,
                                    cmap=cmap,
                                    clim=clim,
                                    border_width=border_width,
                                    border_color=border_color,
                                    **kwargs)

self.grid.remove_widget(self.cbar)
self.cbar_left = self.grid.add_widget(self.cbar, row=0, col=0)
self.cbar_left.width_max = self.cbar_left.width_min = CBAR_LONG_DIM

Somehow, it doesn't refresh and I end up with the previous text being drawn underneath the new text -- which makes everything unreadable.

The second thing I tried is keep track of cbar and simply update its parameters. E.g.

self.cbar.clim = clim
self.cbar.label = label
self.cbar.cmap = cmap 

It works fine for clim and cmap with no change. However, the setter for label directly calls ColorBarVisual @label.setter which should not accept text directly as in init, it is set via label_str as follow:

self._label_str = label_str
self._label = TextVisual(text=self._label_str)

Adding a setter for label_str can be used to then update it via the label setter. So that in ColorBarWidget, the setter for label would be modifying self.label_str. This work fine. E.g.

# In ColorBarWidget
@label.setter
def label(self, label):
        self._colorbar.label_str = label

# In ColorBarVisual
@property
def label(self):
        """ The vispy.visuals.TextVisual associated with the label
        """
        return self._label

@label.setter
def label(self, label):
        self._label = label
        self._update()

@property
def label_str(self):
        return self._label_str

@label_str.setter
def label_str(self, label_str):
        self._label_str = label_str
        self._update()

---

As a side note, I also added the following to ColorBarWidget so that I can modify the color and size of the ticks. I guess this could be added to the lot.

@property
def ticks(self):
        return self._colorbar.ticks

@ticks.setter
def ticks(self, color, font_size):
        self._colorbar.ticks[0].font_size = font_size
        self._colorbar.ticks[1].font_size = font_size
        self._colorbar.ticks[0].color = color
        self._colorbar.ticks[1].color = color

[kmuehlbauer]

@macrocosme

Have the same problem in my application. In #1271 I tried to get all needed functionality within ColorBarWidget and ColorBarVisual without changing the calling conventions (just adding to them).