Highlight difference in rewrite steps

[kwyip]

Aim to fix #190

1. Introduced apply_step_difference_highlighting(current, next_graph) to compute and apply diff_highlight flags on the currently displayed graph.
2. Vertices: when vdata(..., "diff_highlight") is true, draw thicker yellow outlines (selected and unselected states handled).
3. Edges: when edata(..., "diff_highlight") is true, draw a yellow overlay stroke.

For example, in fusing two nodes the new node and a neighboring node are highlighted, as in Lia's example.

But...

• Position-only changes do not highlight.
• Equivalent geometry with different vertex IDs does not highlight.

zxlive_190.mp4

[lia-approves]

Hello, thanks for the PR. It has the issue that Boldi described in #435 :

In particular, when two spiders are fused, it is the nodes and the connecting edge that should be highlighted.

Nodes that don't participate in teh rewrite rule should not be highlighted. Let us know if you have any questions.

[RazinShaikh]

Hi @kwyip thanks for the PR. It looks promising but can you address Lia's comment and also fix the checks that are failing?

[kwyip]

Hi @kwyip thanks for the PR. It looks promising but can you address Lia's comment and also fix the checks that are failing?

Sorry for the late reply. I am currently working on this particular PR right now.

[kwyip]

Hi @lia-approves @RazinShaikh
I have fixed the highlight inconsistencies for fusing, and some other derivation steps. It could be fine now, and fulfill the requirements of two spiders+edge being highlighted.
I have added tests for many different proof steps, e.g. fusing, removal, ZX type, etc. Please let me know if there are any incorrect highlight items, if you are interested in this pull request.

zxlive_190_2.mp4

[boldar99]

Hi,
I have tested the new functionality and it is not correct. When I applied colour change, it highlighted something completely unrelated.

[RazinShaikh]

In addition to that, there should be a toggle in settings to have highlight differences on/off

[kwyip]

Hi @boldar99 @RazinShaikh ,
Let me see what's wrong in the color change scenario. It seems that it was working as intended: highlighting the spider whose color was changed.

zxlive_190_3.mov

Let me also add the toggle functionality.

[RazinShaikh]

Could you try applying many different rewrites (including color change) and see if it always works? I don't remember which sequence of rewrites break this

[boldar99]

Here is an example. Colour change as well as Strong complementarity are highlighted incorrectly.

Screen.Recording.2026-02-28.at.01.11.09.mov

[boldar99]

Other example with fusion:

Screen.Recording.2026-02-28.at.01.14.22.mov

[kwyip]

In addition to that, there should be a toggle in settings to have highlight differences on/off

Hi @RazinShaikh @boldar99 ,
I have added the toggle button in the preference setting. I have also rewritten the “add identity” rule, where the edge was now being highlighted.

I realized what’s wrong in the video above. Essentially, the highlights for every rule (except remove parallel edges, which I don't know how to apply) are correct if one adds a rewrite step, clicks on the previous rewrite, and then views the highlight. If one does that for every step, all the highlights are correct. However, if one adds rewrite steps all at once without clicking anything on the right-side panel, the highlights for most of the steps fail (by some shifts in highlighed vertices).

After realizing the issue and that most users would do the latter, I have not been able to fix it for now.If you could provide any hints, I would really appreciate it.