Introduction and suggestion for schematic netlist highlighting

[Daniel Farrell]

Dear KiCad developers,

 I’ve been using KiCad for a number of years now, and I have a background in software and electronics. I enjoy doing both backend and frontend development. For example, here is a clone of a UI color picker in macOS that I wrote a while ago, https://github.com/danieljfarrell/DFColorWell 100% of the widget is rendered using the native drawing API.

Anyway, to the point!

There is an enhancement to the schematic editor I’d like to add and ask for some advice on how it might be implemented, if it is something you are interested in having.

I really like to use netlist colors in the schematic editor; for me, it improves readability. The enhancement I’d like to make is to add a net “highlight pen” effect color option.

Altium implements this quite nicely; they render a transparent highlight as if it has been drawn by a highlighter pen over the line, and the same colors appear in the PCB editors. See image.

That’s the proposal at a high level.

But the devil is in the details. Some immediate questions that spring to mind are: 1) Does the highlight pen color appear as an addition color option in the Schematic Setup Window? 2) Does everything remain the same, but we just change the rendering?

I think I prefer option 2, with a caveat:

Imagine a text box on the schematic setup window, something like "Highlight." When not enabled, everything is the same as now: the color corresponds to the line color. However, when enabled, the line color is set to a default, and the color is drawn over the line like a highlighter pen.

This has the nice feature that it’s automatically backwards compatible, as it can be made an opt-in rendering feature. It also means that no changes are needed to how colors are brought across to the PCB; there is only one color in both cases; all that changes is how it is rendered. Finally, in terms of persistence in the document, it is just a single Boolean.

It would be very interesting to get your ideas, comments, suggestions on how to implement it, and feedback on whether this is something that would be welcomed.

Regards 

Daniel

[James Jackson]

Hi Daniel,

JamesJ from the forum here!

I've been thinking about how one would implement this feature given the internals of KiCad since your forum post. The devil is, as you say, in the detail. I'd offer up the following thoughts:

1. Currently all net / trace colouring is tied to netclasses. Do we want another (parallel) method of colouring nets? (That's one for us to come to a consensus on)

2. 'Just changing the rendering' is not entirely trivial - the question is from where (and how) is the colour information getting to the right place (this includes schematic rendering of various object classes, pcb rendering of various object classes, and ratsnest rendering)? As a rough guide, have a look through the codebase for calls to GetEffectiveNetClass(); lots of these are to do with finding out rendering colours / line widths. If adding a bespoke method (see Approach 2 below), we'd have to add something to each of these to extract the connection for the object, grab the connection's net name, and query against some net -> colour lookup.

I think there are two ways I'd look to implement this, if we decided we'd like it:

Approach 1:

Leverage the existing netclass mechanisms. The new tool could create a new netclass per colour requested, with a high priority value set, and also add a netclass pattern assignment to match the netclass to the selected net names.

Advantages: Uses existing rendering infrastructure, so the tool only needs to insert netclasses and pattern assignments (which is very easy to do)

Disadvantages: The new netclasses will show up in the status bars (a net with no other netclass assignments with show as: "Netclass: Green and Default", for example). The new netclasses will 'clog up' the netclass setup dialog list. These could both be mitigated by special-casing the net colouring netclasses / pattern matching rules to not be displayed in the netclass setup UI, and to not count them for DRC constraint netclass matching (but this feels a little messy).

Approach 2:

Add a new data structure which maps netclass names to colour overrides. Where we check nets for colour from netclasses, we also add a check to see if there is a net colour override.

Advantages: Doesn't impact on the netclass asignments

Disadvantages: Another layer of complexity in rendering colour choice

Both of these have a shared disadvantage in that the only consistent identifier for a net is its name. And these are mutable if, for example, one adds a higher priority driver to a net, or changes a driving component designation or pin. As far as I can think, there's no easy way to map changes in net names on schematic edits, so sometimes colours might just drop on net name changes.

UI considerations aside, either method actually wouldn't be that hard to do (famous last words...), and I'd be happy to implement it (I've had my head buried deep in the rendering code for the multiple netclass work I recently implemented). I'd welcome comment from the other lead devs on if we want another way to colour nets though. FWIW, I think this would be a useful addition, but that's a weakly held view.

Yours,

James.

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[Jon Evans]

Hi Daniel,

KiCad nightly (for V9) already has a feature to transfer schematic netclass colors to the board (this isn't done automatically because sometimes you want different colors in each place). This seems to address one of your desires.

It seems like the crux of what you want is a rendering change: instead of showing net colors as a change in the line color, you show them as a "highlight", or in other words, a different line that is thicker and underneath the wire/bus.

I think this should be done as an option (either a user preference, or a schematic/project option -- I would lean towards user preference here, but don't feel strongly) to change how netclass colors are rendered.

As for the technical implementation -- it would require a new virtual rendering layer, I think.  Search the code for LAYER_SELECTION_SHADOWS to see an example of how it is done.  These rendering layers are used for Z-ordering since there cannot be different Z-order within a single layer.

@James -- unless I'm missing something, I think this may be simpler than you put it.  Schematic line color is not limited to netclasses, but netclasses are the only mechanism for transferring line color to the PCB.  I don't think the proposed feature should be tied to any structural changes to how color works or how netclasses work -- it's really just a preference for how lines are drawn in the schematic editor, I think.

Best,

Jon

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[James Jackson]

Jon,

I think we've interpreted the feature differently (but not necessarily orthogonally...). I read the ask as being able to colour nets (be that rendered as you say with a new highlight layer, or as we currently do). As far as I can see, the only way to currently colour a net is through netclasses. We can also set the colour of individual schematic wires, but that (to my mind) doesn't hit the 'colour a net' request. Have I missed another method of colouring nets?

I think the request here is twofold: a way to colour nets (not just individual wires, and not just be using netclass directives), and a new UI method of quickly assigning colour to nets (which looks like an extension of the net highlighting tool - i.e a. 'colour this net please' tool)..

I haven't used the equivalent Altium feature referred to in the original email, but the way I read the docs is if I add another wire to a coloured net, that wire will also pick up the net colour. I don't think, without assigning a netclass, we have a way to do this at the moment (nor, as you say, do we have a way to transfer anything other than a netclass-defined colour to the PCB, which seems an integral part of this feature for assisting in laying out complex boards).

Yours,

James.

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[James Jackson]

(For further clarity - I'm looking specifically at how to do this in eeschema. We do have the net colouring mechanisms in pcbnew we could integrate this with to handle that side of things.).

[exlabs]

Hi James, John,

Thank you both for the welcoming discussion.

I won't comment too much on the technical implementation side here - but I will get a workspace setup and search the terms you mentioned.

Just to clarify, yes, I'm mainly interested in adding a new way of rendering netclass colours in the schematic.

For example, I have used my incredible Photoshop skills to add a checkbox to the Schematic Setup Window.

Checkbox disable: No rendering changes; color is the line color.
Checkbox enabled: line color is a default value, and the color is drawn in a highlighter pen style.

I don't want to suggest that this is best UI, or the best way of implementing it because I don't know the codebase at all! Please take this purely at a functional level - you can imagine how the feature would work.

By posting the Altium screenshot, I didn't mean to imply anything more complicated than what is written above; it illustrated the highlighter pen rendering style quite nicely.

I will watch the discussion develop and chime in when I have something useful to say.

Daniel

[James Jackson]

Hi Daniel,

Aha - I read too much in to your screenshot! In which case, ignore most of what I said, and listen to Jon ;-)

Sounds like a separate rendering layer is the way forwards. Let me see if I can knock something up as a proof of concept.

Yours,

James.

[James Jackson]

Daniel,

Something like this? Need to tidy up some UI stuff (and make it apply to buses with netclass colours) but is this the kind of thing you're looking for?

Yours,

James.

[exlabs]

Hi James,

Yes, this is exactly what I was hoping for! Wow, you did that so fast. It would be great to see your Commit to learn how you accomplished this.

This is totally usable to my eye, but here are some ascetic suggestions you might consider:

1. Swap the layer order to place the highlight on top of the wire: this will be more natural-looking as the wire has been highlighted by a pen.
2. Offset the highlight slightly so that it does not touch the beginning or end of the wire: it stays away from the component symbol.

That's all I got—great job!

Regards,

Daniel

[Jon Evans]

> Offset the highlight slightly so that it does not touch the beginning or end of the wire: it stays away from the component symbol.

This is not trivial.  I'd advise against spending time on this personally.

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[James Jackson]

Yep, I wasn't going to try implementing that.

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[James Jackson]

Daniel,

Now committed to the v9 branch, so will be available in nightly builds soon. If you're interested in taking a look, this is the commit:

https://gitlab.com/kicad/code/kicad/-/commit/6371b15aa4bbe4770d10a38bcd84b62c20da7e4e

Currently the highlight width and transparency aren't configurable (but it would be trivial to add this). Also, there is an edge-case whereby a custom netclass colour that is the same a the default wire or bus colour won't have highlights drawn. To fix that would need some significant re-architecting of the schematic painting colour fetching code, and I think it's likely to be a very rare edge case, so not worried about that for now.

Yours,

James.

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[exlabs]

Hi James,

Thanks so much for all your hard work! The commit touched a lot of files, there is no way I could have figured all that out in a day so I'm delighted you were interested to do this.

I will grab a copy of the nightly build :)

Regards,

Daniel

[James Jackson]

Daniel,

No problem at all - I've had my head in that code a lot recently so it wasn't too difficult. I've also just added the ability to configure the thickness and opacity of the highlights. Note that these settings are now all in the application-level Schematic Editor -> Display Options settings.

Yours,

James.

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