Follow up work on `Circuit._repr_svg_`

[freyam]

Is your feature request related to a use case or problem? Please describe.

@mpharrigan did an amazing job working on adding the SVG representation for a Cirq.Circuit. He left some TODOs in his Issue (#2313). In this issue, I plan to address them and open them for further discussion.

Describe the solution you'd like
Listing the tasks from #2313,

Bugs

• [BUG] Take care of the SVG circuits when the cirq.Moment() is empty (Currently, it fails).
• [BUG] Refactor the rendering code such that circuits do not require integer coordinates for spacing routines.
• [BUG] Implement a dynamic horizontal spacing framework for the rows in the SVGs of the circuits.

Design (A detailed RFC will be opened for this)

• [DESIGN] Come up with a way to visualize custom gates (MatrixGate).
• [DESIGN] Revamp the SVG output and make it more informative, illustrative, and colorful.

Testing

• [TESTING] Add thorough tests.

Ideally, once this issue is fixed, we can think of moving the SVG representation under cirq.Circuit itself.
This would require moving the code out from contrib.

Integration

• [IMPLEMENTATION] Generalize the code used in cirq-core/cirq/circuits/_block_diagram_drawer.py and cirq-core/cirq/contrib/svg/svg.py to draw the blocks.
• [INTEGRATION] Dissolve the SVGCircuit class and integrate SVGCircuit._repr_svg_ in cirq.Circuit (or even cirq.AbstractCircuit).

Additional context (e.g. screenshots)

Current Implementation

What is the urgency from your perspective for this issue? Is it blocking important work?
P2 - we should do it in the next couple of quarters

cc @tanujkhattar

[mpharrigan]

Awesome!

[tanujkhattar]

@freyam Thanks for opening up the issue and taking this up!

Our Cirq roadmap item on adding a verbose logging mode to Transformers for easier inspection and understanding will definitely make use of the improved SVGCircuit framework. cc #4483

[vanhalen42]

Hi, I'm interested and would like to work on this as well!

[freyam]

Update

The bugs have been taken care of (#4535)

• [BUG] Take care of the SVG circuits when the cirq.Moment() is empty (Currently, it fails).
• [BUG] Refactor the rendering code such that circuits do not require integer coordinates for spacing routines.
• [BUG] Implement a dynamic horizontal spacing framework for the rows in the SVGs of the circuits.

Now, the next step is to figure out a nice way to represent custom gates. Currently, it just shows a ? in a box for every instance of MatrixGate class. It has the following attributes:

Cirq/cirq-core/cirq/ops/matrix_gates.py

Lines 65 to 68 in ab335e6

	self._matrix = matrix
	self._qid_shape = tuple(qid_shape)
	self._name = name
	m = int(np.prod(self._qid_shape, dtype=np.int64))

@tanujkhattar how do you want me to go forward with it? Would you like me to prepare an RFC and bring this up in the next Cirq Cync?

I have created a demo PR (#4630) for this.