Added span parameter for datashade operation

[philippjfr]

Not sure span is the best name for this parameter but I just used the datashader argument name for now. Maybe clims or color_range would be better?

[jbednar]

I definitely don't like the name span. Is clims already in use for this purpose in HoloViews? If not it's more like a value_range.

[jlstevens]

I don't think clims would clash in this case and it is clearer/more intuitive than span. Seems like the issue is that this isn't what this argument is called in datashader.

[philippjfr]

Seems like the issue is that this isn't what this argument is called in datashader.

We already changed a bunch of the argument names because they're not very intuitive.

[jbednar]

The datashader API needs some tidying up before I'm ready to call it 1.0, so don't worry about what it's called in datashader. I think HV should be supplying whatever dimension range it normally uses for non-datashader plots, though it could be convenient to provide an argument to shade that makes it simple to override that value when needed.

[jbednar]

@philippjfr, can you please rename span to whatever the best match to HoloViews usage is, and then make it respect the dimension's range if not overridden here?

[philippjfr]

@philippjfr, can you please rename span to whatever the best match to HoloViews usage is, and then make it respect the dimension's range if not overridden here?

Was going to go with value_range and already have those changes applied locally. Will push in a minute.

[philippjfr]

Might go back to clims since it's shorter.

[jlstevens]

I also think clims is better: this operation outputs and RGB so there is color mapping and from what I understand this parameter is really about controlling colors.

[jbednar]

clims is fine by me. It's an edge case; the actual parameter has nothing to do with colors, and applies to the value rather than to any colors, but it has no effect on anything but colors, in the end.

[jlstevens]

Looks good to me and the tests are green. Merging.