Clean up text drawer compression issues

[enavarro51]

Summary

Fixes several problems with vertical_compression in the text circuit drawer.

Details and comments

There is an option for the text circuit drawer called vertical_compression that allows a user to choose how much vertical spacing there is between the horizontal lines. If 'high is chosen, then only 1 line will display between a pair of wires and in certain cases it's possible characters will overwrite other characters or drawing elements. If low is chosen, 2 lines will be used between every pair of lines and no overwriting will occur.

If medium, which is the default, is chosen, the compression starts out the same as high, but the drawer then tries to detect areas where overwriting would occur and expands the vertical to 2 lines where that would happen. The detection of these areas was not working consistently.

low compression was also causing connections between a gate and a control to be broken. Finally there were areas where connections for conditional gates were breaking. These drawings show 2 of the problems followed by a corrected drawing.

qr_0: ─░─────────────
       ░       ┌───┐ 
qr_1: ─░───■───┤ X ├─
       ░   │   Bar─1 
qr_2: ─░───┼─────░───
       ░ ┌─┴─┐   ░   
qr_3: ───┤ X ├───░───
         └───┘   ░   

       a             
qr_0: ─░─────────────
       ░       ┌───┐ 
qr_1: ─░───■───┤ X ├─
       ░   │   └───┘ 
       ░   │   Bar 1 
qr_2: ─░───┼─────░───
       ░ ┌─┴─┐   ░   
qr_3: ───┤ X ├───░───
         └───┘   ░   

qr_0: ────────────
            ┌───┐ 
qr_1: ──■───┤ X ├─
        │   └───┘ 
            Bar 1 
qr_2: ────────░───
      ┌─┴─┐   ░   
qr_3: ┤ X ├───░───
      └───┘   ░   

qr_0: ────────────
            ┌───┐ 
qr_1: ──■───┤ X ├─
        │   └───┘ 
        │   Bar 1 
qr_2: ──┼─────░───
      ┌─┴─┐   ░   
qr_3: ┤ X ├───░───
      └───┘   ░   

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[coveralls]

Pull Request Test Coverage Report for Build 2982196345

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.002%) to 84.221%

---

Files with Coverage Reduction	New Missed Lines	%
qiskit/extensions/quantum_initializer/squ.py	2	79.78%

Totals
Change from base Build 2982049604:	0.002%
Covered Lines:	57176
Relevant Lines:	67888

---

💛 - Coveralls

[jakelishman]

Thanks Edwin! One minor comment about the tests, but I think the new behaviour is probably a pretty reasonable default.

[jakelishman]

Can we revert this test case? The behaviour that appears with this PR and this test is probably something we want to make a positive decision on, and potentially test both it and your new form (with the space not aligned).

For clarity: with this PR, the original test produces

        ┌──────┐
q_0: |0>┤ my h ├
        └──┬───┘
q_1: |0>───■────
         my║ch
   c: 0 ═══■════
          0x1

instead. I feel like that (^) behaviour is probably actually suitable for vertical_compression=medium - it compresses vertically when there's a "space" so nothing visible gets erased, whereas "high" always compresses and "low" never does.

Perhaps leave the test as-is, and add your new one as a separate case?

[enavarro51]

Ha, I was hoping nobody would notice that. It works visually either way and it's probably a pretty rare case. I'll add the old test back with the new one.

[jakelishman]

Looks good, thanks! Would you mind adding a short bugfix release note? Sorry - I missed that it wasn't there first time round apparently.

[jakelishman]

Looks great, thanks for the changes!