fix: correct scale-mode object_transform to keep the gizmo pivot fixed

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fixed the spinner getting stuck after a WebSocket reconnect: spinner messages are now persisted (under a stable `obj_id="spinner"`) like other viewer state, so a reconnecting client sees the current spinner state instead of missing a "stop" it never received.
 - Fixed large model uploads silently dropping the WebSocket connection: the server's `ws_max_size` is raised from uvicorn's 16 MiB default to 256 MiB.
+- Fixed scale-mode `object_transform` on `Shape` geometry (Box, Sphere, ...) moving the object's pivot away from where the gizmo showed it: the full delta is now applied to `frame.point`, only the rotation to the frame axes, and the resize goes through `Shape.scale()`.
 
 ### Removed
 

src/compas_threejs/viewer/inbox.py

@@ -13,6 +13,65 @@
 
 console = Console()
 
+_SCALE_TOLERANCE = 1e-9
+
+
+def _apply_transform_with_scale(geometry, transformation) -> None:
+    """Applies `transformation` to `geometry`, resizing it too if the transformation
+    carries a scale component (e.g. a TransformControls "scale" gizmo drag).
+
+    `Shape.transform` (the base class for Box/Sphere/...) only ever applies to the
+    shape's frame, and explicitly does not support scale - see its own docstring:
+    "only (combinations of) translations and rotations are supported. To scale a
+    shape, use the Shape.scale method." A scale-mode gizmo drag produces exactly the
+    kind of delta transform that docstring warns about, so passing it straight to
+    `.transform()` silently drops the resize entirely (confirmed empirically:
+    `Box.xsize` never changes).
+    """
+    scale, _shear, rotation, translation, _projection = transformation.decomposed()
+    sx, sy, sz = scale.matrix[0][0], scale.matrix[1][1], scale.matrix[2][2]
+    has_scale = not (abs(sx - 1.0) < _SCALE_TOLERANCE and abs(sy - 1.0) < _SCALE_TOLERANCE and abs(sz - 1.0) < _SCALE_TOLERANCE)
+
+    if not has_scale:
+        # No resize at all - Shape.transform (== frame.transform) already does
+        # exactly the right thing here: moves the point, rotates the axes.
+        geometry.transform(translation * rotation)
+        return
+
+    if not hasattr(geometry, "frame"):
+        # Not a Shape (e.g. a Point/Mesh/Polyline, transformed via its own raw
+        # coordinates) - unlike Shape, these support a general affine `.transform()`
+        # including scale directly (Shape is the one deliberate exception - see its
+        # own docstring above), so the full delta can just be applied as-is.
+        geometry.transform(transformation)
+        return
+
+    # A Shape (Box, Sphere, ...) being resized: frame.point needs the *full* delta
+    # (translation AND scale) applied directly - not `Shape.transform()` (drops scale
+    # entirely, see above), and not just the rigid translation*rotation part either.
+    # A scale-mode gizmo drag keeps the object's own pivot fixed and only changes its
+    # scale factor, so relative to the object's own drag-start frame this delta is a
+    # "scale about that original point" transform (in 1D: T(pos*(1-k)) * S(k)) -
+    # applying only the rigid part to the point recovers pos*(2-k), not pos: a visible
+    # jump to the wrong location, not the pivot-preserving resize the gizmo showed.
+    # Applying the full delta to the point is the correct way to relocate a point
+    # under a pivot-relative scale; the frame's own axes only ever need the rotation
+    # part (a Vector's `.transformed` already ignores translation, and has no "size"
+    # for scale to distort).
+    geometry.frame.point = geometry.frame.point.transformed(transformation)
+    geometry.frame.xaxis = geometry.frame.xaxis.transformed(rotation)
+    geometry.frame.yaxis = geometry.frame.yaxis.transformed(rotation)
+
+    try:
+        geometry.scale(sx, sy, sz)
+    except TypeError:
+        # Uniform-scale-only geometry (e.g. Sphere.scale(factor)) - average the three
+        # factors rather than silently dropping a non-uniform resize on the floor.
+        geometry.scale((sx + sy + sz) / 3.0)
+    except NotImplementedError:
+        console.log(f"[yellow]{type(geometry).__name__} does not support scaling - resize from this drag was dropped[/yellow]")
+
+
 # Maps a frontend-creatable type name to its COMPAS constructor and the numeric
 # parameter names a "create_geometry" message is allowed to set on it.
 _CREATABLE_TYPES = {
@@ -193,7 +252,7 @@ def _handle_object_transform(self, message, outbox, workspace_id):
 
         transformation = Transformation.from_matrix(matrix)
         with self.lock:
-            geometry.transform(transformation)
+            _apply_transform_with_scale(geometry, transformation)
 
         if self.app is not None:
             self.app.get_workspace(workspace_id).update_geometry(geometry)

tests/test_object_transform_scale.py

@@ -0,0 +1,97 @@
+import unittest
+
+from compas.geometry import Box
+from compas.geometry import Frame
+from compas.geometry import Point
+from compas.geometry import Rotation
+from compas.geometry import Scale
+from compas.geometry import Sphere
+from compas.geometry import Translation
+
+from compas_threejs.viewer.inbox import _apply_transform_with_scale
+
+
+class ObjectTransformScaleTest(unittest.TestCase):
+    def test_box_translate_and_rotate_only_matches_plain_transform(self):
+        # No scale component - should behave exactly like geometry.transform(delta),
+        # the pre-fix (and still correct, for this case) behavior.
+        box = Box(xsize=1, ysize=2, zsize=3, frame=Frame(Point(0, 0, 0), [1, 0, 0], [0, 1, 0]))
+        delta = Translation.from_vector([1, 2, 3]) * Rotation.from_axis_and_angle([0, 0, 1], 0.4)
+
+        reference = box.copy()
+        reference.transform(delta)
+
+        _apply_transform_with_scale(box, delta)
+
+        self.assertAlmostEqual(box.frame.point.x, reference.frame.point.x)
+        self.assertAlmostEqual(box.frame.point.y, reference.frame.point.y)
+        self.assertAlmostEqual(box.frame.point.z, reference.frame.point.z)
+        self.assertEqual((box.xsize, box.ysize, box.zsize), (1, 2, 3))
+
+    def test_box_scale_resizes_and_recenters(self):
+        # Box.transform() alone silently drops any scale component (it only applies
+        # to the frame - see its own docstring) - this is the bug being fixed.
+        box = Box(xsize=1, ysize=1, zsize=1, frame=Frame(Point(0, 0, 0.5), [1, 0, 0], [0, 1, 0]))
+        delta = Translation.from_vector([1, 0, 0]) * Scale.from_factors([2, 1, 1])
+
+        _apply_transform_with_scale(box, delta)
+
+        self.assertEqual((box.xsize, box.ysize, box.zsize), (2.0, 1.0, 1.0))
+        self.assertAlmostEqual(box.frame.point.x, 1.0)
+        self.assertAlmostEqual(box.frame.point.z, 0.5)
+
+    def test_scale_drag_keeps_the_gizmo_pivot_fixed_not_shifted(self):
+        # Reproduces the reported "box jumps to another location after scaling" bug.
+        # A TransformControls scale-mode drag keeps the object's OWN pivot fixed and
+        # only changes its scale factor (confirmed against three.js's own source) -
+        # relative to the object's drag-start frame, that delta is a "scale about the
+        # object's original center" transform, which for a center at x=pos and factor
+        # k is T(pos*(1-k)) * S(k) in 1D. Applying only the rigid (translation *
+        # rotation) part of that to frame.point - the pre-fix behavior - recovers
+        # pos*(2-k), not pos: for pos=0.36, k=1.6667, that's 0.12, a full grid unit
+        # (0.24) away from the correct, gizmo-matching 0.36. The earlier version of
+        # this test suite never caught this because it only ever used a starting
+        # frame.point at x=0, where the wrong formula and the right one coincide.
+        pos = 0.36
+        k = 1.6667
+        delta = Translation.from_vector([pos * (1 - k), 0, 0]) * Scale.from_factors([k, 1, 1])
+        box = Box(xsize=0.72, ysize=1, zsize=1, frame=Frame(Point(pos, 0, 0), [1, 0, 0], [0, 1, 0]))
+
+        _apply_transform_with_scale(box, delta)
+
+        self.assertAlmostEqual(box.frame.point.x, pos)
+        self.assertAlmostEqual(box.xsize, 0.72 * k)
+
+    def test_non_uniform_scale_on_uniform_only_shape_falls_back_to_average(self):
+        # Sphere.scale(factor) only takes one factor - a non-uniform delta (e.g. a
+        # per-axis TransformControls scale drag) can't be applied exactly, so this
+        # averages the three factors rather than crashing or dropping the resize.
+        sphere = Sphere(radius=1, frame=Frame(Point(0, 0, 0)))
+
+        _apply_transform_with_scale(sphere, Scale.from_factors([2, 3, 4]))
+
+        self.assertAlmostEqual(sphere.radius, 3.0)
+
+    def test_scale_on_a_frameless_geometry_uses_the_full_delta_directly(self):
+        # A Point (or Mesh/Polyline) has no .frame at all - unlike Shape, its own
+        # .transform() isn't scale-blind, so the full delta can go straight through.
+        point = Point(1, 2, 3)
+
+        _apply_transform_with_scale(point, Scale.from_factors([2, 3, 4]))
+
+        self.assertAlmostEqual(point.x, 2.0)
+        self.assertAlmostEqual(point.y, 6.0)
+        self.assertAlmostEqual(point.z, 12.0)
+
+    def test_identity_scale_is_a_no_op_and_does_not_call_scale(self):
+        box = Box(xsize=1, ysize=1, zsize=1, frame=Frame(Point(0, 0, 0), [1, 0, 0], [0, 1, 0]))
+        called = []
+        box.scale = lambda *a: called.append(a)  # would fail loudly if invoked wrongly
+
+        _apply_transform_with_scale(box, Translation.from_vector([1, 0, 0]))
+
+        self.assertEqual(called, [])
+
+
+if __name__ == "__main__":
+    unittest.main()