[BUG] grid_line_alpha value of '1.0' doesn't work but '0.99' does work

[ribeirompl-soldersmith]

Software versions

Python version : 3.8.3 (default, Jul 2 2020, 17:30:36) [MSC v.1916 64 bit (AMD64)]
IPython version : 8.1.1
Tornado version : 6.1
Bokeh version : 3.0.2
BokehJS static path : .......\lib\site-packages\bokeh\server\static
node.js version : (not installed)
npm version : (not installed)
Operating system : Windows-10-10.0.19041-SP0

Expected behavior

When using the dark_minimal theme, and setting the grid_line_alpha value to 1 (or 1.0):
I would expect the grid line to become opaque.

Observed behavior

The grid line alpha does not change.

Example code

from bokeh.plotting import curdoc, figure, show

curdoc().theme = "dark_minimal"
fig = figure()
fig.line([1, 2, 3, 4], [1, 2, 3, 4])
fig.title = "Before (grid_line_alpha=0.25 from theme)"
show(fig)

fig.grid.grid_line_alpha = 1.0
fig.title = "After (grid_line_alpha=1.0)"
show(fig)

fig.grid.grid_line_alpha = 0.99
fig.title = "After (grid_line_alpha=0.99)"
show(fig)

I expect to see the "After" plot having a more opaque grid line, than the "Before" graph.
However, they look the same.

But, if I instead set the grid_line_alpha to 0.99, then it visibly changes.

Screenshots

[mattpap]

The default value is 1.0, so setting the property to the same value is a no-op. We need to mark such properties as "dirty", so that when applying a theme, the default-looking value is preferred over the themed default.

[bryevdv]

That was my first thought as well, but it's also a little weird. class_default and instance_default return the themed default, so this shouldn't be a no-op:

bokeh/src/bokeh/core/property/descriptors.py

Lines 308 to 335 in 0326ae1

	def class_default(self, cls: type[HasProps], *, no_eval: bool = False):
	""" Get the default value for a specific subtype of ``HasProps``,
	which may not be used for an individual instance.
	Args:
	cls (class) : The class to get the default value for.
	no_eval (bool, optional) :
	Whether to evaluate callables for defaults (default: False)
	Returns:
	object
	"""
	return self.property.themed_default(cls, self.name, None, no_eval=no_eval)
	def instance_default(self, obj: HasProps) -> T:
	""" Get the default value that will be used for a specific instance.
	Args:
	obj (HasProps) : The instance to get the default value for.
	Returns:
	object
	"""
	return self.property.themed_default(obj.__class__, self.name, obj.themed_values())

So maybe there a bug in that computation.

[bryevdv]

We need to mark such properties as "dirty"

@mattpap FYI there has also been some recent talk around supporting light/dark modes via themes, so we will want to make sure all requirements are considered and make sure everyone is on the same page. I'd advise making a discussion first before embarking on any wider or structural changes to properties (making an issue for light/dark is on my short-term to-do).

[mattpap]

I don't see this bug as a theming issue, but as a simple bokeh doesn't respect user inputs type of issue.

[gauravk97]

Hi @bryevdv @mattpap ,

I was just checking the repository and came across this issue, I feel like picking it up. Should I go ahead and take a look at it? Asking here in case this issue is being fixed by someone already. What would you say?

[bryevdv]

@gauravk97 If you want to take a look at things, that's great, and we would be happy to receive and review any proposed solution in a PR. I should be up front that this issue intersects the low-level foundational property system, so it will require some extra care.

[gauravk97]

Sure, I was just itching to code some python. If you have some other beginner issue (for this repo), I'd be happy to look into that as well. Otherwise, I will continue checking this one.

[bryevdv]

@gauravk97 this one might be good to look at https://github.com/bokeh/bokeh/issues/12345 (text literal to try to avoid linking unrelated issues)