Make mpl colors and other styles fully configurable by users with a json load

[enavarro51]

What is the expected enhancement?

In #5063, the IQX color scheme was added as an option to the mpl drawer. The style dict entry, 'displaycolor' was expanded to include new gates and to allow for entering both gate and text color for each gate type. This expands color choices to include dark gate colors with light text. This first phase was done by creating 3 classes in qcstyle.py.

In this next phase, this can be reduced to 1 default class and the additional styles would be read in from json files. I don't believe users should be allowed to edit these 3 json files - default, iqx, and bw - directly, but they can copy these and create new styles of their own.

This issue proposes to make default, iqx, and bw json style files part of qiskit, perhaps in a styles directory under the visualization directory. User json files should go in a fixed place, perhaps in a styles directory under ~/.qiskit.

The code for reading in the json files already exists, though there is only minimal error checking currently. Deciding on the locations for the files is the main issue.

We might want to look at any possible special cases, like the controlled classical gates in iqx and see if any of these can be addressed in a generic way. Right now all a user can do with color is change the colors of the specific gate names in 'displaycolor'.

Any of the other documented style dict items can be set in the user json file. The user can create a partial style dict in the file, and only those elements entered will be changed for that style.

The user interface is simple - qc.draw('mpl', style='user_style1.json')

[1ucian0]

In this next phase, this can be reduced to 1 default class and the additional styles would be read in from json files. I don't believe users should be allowed to modify these 3 styles - default, iqx, and bw - directly, but they can copy these and create new styles of their own.

Why not? It could be possible to give priority the entries to displaycolor over the one on name:

style={'name': 'iqx',
       'displaycolor': {'u1': ('#FFFFFF', '#000000')}

Or the equivalent user_style1.json:

{"name": "iqx",
 "displaycolor": {"u1": ["#FFFFFF", "#000000"]}
}

[enavarro51]

Why not? It could be possible to give priority the entries to displaycolor over the one on name:

style={'name': 'iqx',
'displaycolor': {'u1': ('#FFFFFF', '#000000')}

This would still be fine. Changes can still be made at runtime. I'm just referring here to the json files that will contain the standard 3 styles.

[enavarro51]

In working on the style dictionary for the 'mpl' drawer I've come upon several historic bits of code and docs that need to be cleaned up.

• When the 'mpl' and 'latex' drawers were split up (Split out latex backend into a separate module #1111) , I believe the intention was for the 2 drawers to share the 'qcstyle.py' style information. At the top of the 'latex' code, the BWStyle is loaded from qcstyle, but is never referenced in the drawer after that, so BWStyle has no effect on what is displayed. This load and the passed style parameter to 'latex' should be removed.
• There are 3 items in the style dict that are never implemented in any of the code, but are in the docs.
  • latexdrawerstyle (bool): When set to True, enable LaTeX mode, which will draw gates like the latex output modes.
  • compress (bool): If set True, draw a compressed circuit.
  • usepiformat (bool): When set to True, use radians for output.

'latexdrawerstyle' was probably intended to be used by the 'latex' drawer, but it's not.

Don't know what the history is for 'compress', and there is a 'vertical_compression' parameter for the 'text' drawer, but I don't know of any way you would compress the 'mpl' drawer.

And 'usepiformat' I assume is not relevant, since we always use radians?

The plan is to remove these from the docs and show a deprecation warning if any of the 3 items are put in a style dict by a user. Any input would be appreciated.