feat: properly update last used coordinate "()"

[bendix4620]

The problem

Currently, zap does not allow cetz to update the last used coordinate

#import "@preview/zap:0.5.0"
#set page(width: auto, height: auto, margin: 5pt)

#zap.circuit({
  import zap: *
  resistor("r1", (), (2, 0))
  resistor("r2", (), (2, 2))
})

what I got	what I want

Proposed Solution

change the scoping and coordinate resolution to allow updates of ctx.prev:

#let component(...) = {
  ...

  // resolve coordinates and update the context
  get-ctx(ctx => {
    let (ctx, ..position) = cetz.coordinates.resolve(ctx, ..position)
    set-ctx(_ => { ctx }) // update the context, so "ctx.prev" is correct
  
    // wrap all component logic/drawing inside scopes or groups, so that it does not alter the context any further
    scope({
      // draw the component here
      ...
    })
    // the scope/group will reset the context (and keep the anchors)
  })
}

Contribute

• I am willing to submit a pull request for this feature
• I can help with testing this feature

[bendix4620]

Further questions

Should this be a wrapper?

Using a wrapper could be beneficial if more features not based on component() will be added (like wire and node).
The wrapped could handle all the preprocessing (resolving coordinates, styles and scopes), see below. While it does shorten the component function, I fear it might still be clunky to use

#let resolve-ctx(position, style, wrapped) = {
  get-ctx(ctx => {
    // resolve coordinates
    let (ctx, ..position) = cetz.coordinates.resolve(ctx, ..position)
    // update the context, so "ctx.prev" is correct
    set-ctx(_ => { ctx }) 

    // resolve style

    scope(wrapped(position, style))
  })
}

#let component() = {
  // preprocess parameters, e.g. assertions
  
  resolve-ctx(position, style, (position, style) => {
    // draw component

    // draw labels

    // draw decoration

    // draw debug
  })
}

Should I add this before the styling system is reworked?

In this case I would not add style resolving to the wrapper, as it might get too convoluted (for example debug and label styles are handled separately from the component styling afaict). The wrapper has dramatically less appeal this way.

[bendix4620]

Using a wrapper kind of requires cetz 0.5.0 to release...

The following fails, "bar" is not accessible inside "foo".

#import "@preview/cetz:0.4.2"
#set page(width: auto, height: auto, margin: 5pt)

#cetz.canvas({
  import cetz.draw: *
  group(name: "foo", {

    // this would be the component
    scope(ctx => {
      group(name: "bar", {
        anchor("default", ())
      })
    })

  })
  circle("foo.bar", radius: .5, stroke: red)
})

(it's already fixed in the dev version)

[github-actions]

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