[bug]: Stacks are not properly getting anchored

[BenJamesBen]

What seems to be the problem? 🤔

From #5991 (comment):

...I seem to remember that stacks are not properly getting anchored, and I suspect that's something we need to look into.
Then again, it's a bit niche, so not urgent.

(I don't know anything else about this possible problem.)

Design / Plugin / Package 🧐

packages/core

Additional context

No response

[joostdecock]

You can see here how one of the parts of Lumina is trending away when sampling the seat circumference measurements.

Setting points.anchor in the design should make that point the anchor point for sampling, but that does not seem to work.

That's the bug :)

[BenJamesBen]

Is this issue seen only with Lumina? I suspect that Lumina is actually shifting the location of the Waistband part relative to (0,0) based on Seat Circumference.

[BenJamesBen]

--- a/designs/lumina/src/waistband.mjs
+++ b/designs/lumina/src/waistband.mjs
@@ -70,6 +70,16 @@ export const waistband = {
       return part.hide()
     }
 
+    // Normalize part location relative to anchor
+    const ydiff = points.waistBack.y
+    points.waistBack = points.waistBack.shift(90, ydiff)
+    points.waistFront = points.waistFront.shift(90, ydiff)
+    points.waistFrontCP = points.waistFrontCP.shift(90, ydiff)
+    points.waistBackCP = points.waistBackCP.shift(90, ydiff)
+    paths.waist = new Path()
+      .move(points.waistBack)
+      .curve(points.waistBackCP, points.waistFrontCP, points.waistFront)
+
     points.waistbandFront = points.waistFront.shift(270 + angle, waistbandSize)
     points.waistbandBack = points.waistBack.shift(270 - angle, waistbandSize)

[BenJamesBen]

points.anchor and points.gridAnchor functionality is currently disabled in package/core/src/stack.mjs. Instead of using Stack.getAnchor(), the anchor is hardcoded to new Point(0, 0).

  // Add transform
  //this.anchor = this.getAnchor()
  // FIXME: Can we be certain this is always (0,0) /
  this.anchor = new Point(0, 0)

The change to hardcoded (0, 0) was made on 2023-09-17 via #2827 and 0b18d81.

[joostdecock]

Yes, that's the bug, or rather, it was never fully implemented.
September 2022 was when I was making sweeping changes to core since we had just decided a few weeks prior to start working on v3.
It would take another year for v3 to be released, and this is something that was never implemented. Overlooked, forgotten, or just not deemed critical to block the v3 release.

So, I think that we should fix that and implement proper anchor support in stacks.