Introduce TransformRelation component

crates/store/re_types/definitions/rerun/archetypes/transform3d.fbs

@@ -3,9 +3,10 @@ namespace rerun.archetypes;
 
 /// A transform between two 3D spaces, i.e. a pose.
 ///
-/// All components are applied in the inverse order they are listed here.
-/// E.g. if both a 4x4 matrix with a translation and a translation vector are present,
-/// the translation is applied first, followed by the matrix.
+/// From the point of view of the entity's coordinate system,
+/// all components are applied in the inverse order they are listed here.
+/// E.g. if both a translation and a max3x3 transform are present,
+/// the 3x3 matrix is applied first, followed by the translation.
 ///
 /// Each transform component can be listed multiple times, but transform tree propagation is only possible
 /// if there's only one instance for each transform component.
@@ -20,10 +21,6 @@ table Transform3D (
   "attr.docs.category": "Spatial 3D",
   "attr.docs.view_types": "Spatial3DView, Spatial2DView: if logged above active projection"
 ) {
-  /// The transform
-  // TODO(#6831): remove.
-  transform: rerun.components.Transform3D ("attr.rerun.component_optional", order: 1000);
-
   /// Translation vectors.
   translation: [rerun.components.Translation3D] ("attr.rerun.component_optional", nullable, order: 1100);
 
@@ -39,6 +36,9 @@ table Transform3D (
   /// 3x3 transformation matrices.
   mat3x3: [rerun.components.TransformMat3x3] ("attr.rerun.component_optional", nullable, order: 1500);
 
+  /// Specifies the relation this transform establishes between this entity and its parent.
+  relation: rerun.components.TransformRelation ("attr.rerun.component_optional", nullable, order: 1600);
+
   // --- visual representation
 
   /// Visual length of the 3 axes.

crates/store/re_types/definitions/rerun/components/channel_data_type.fbs

@@ -3,7 +3,9 @@ namespace rerun.components;
 /// The innermost datatype of an image.
 ///
 /// How individual color channel components are encoded.
-enum ChannelDataType: byte {
+enum ChannelDataType: byte (
+    "attr.docs.unreleased"
+) {
     /// 8-bit unsigned integer.
     U8 (default),
 

crates/store/re_types/definitions/rerun/components/transform_relation.fbs

@@ -0,0 +1,20 @@
+namespace rerun.components;
+
+/// Specifies relation a spatial transform describes.
+enum TransformRelation: byte (
+    "attr.docs.unreleased"
+) {
+    /// The transform describes how to transform into the parent entity's space.
+    ///
+    /// E.g. a translation of (0, 1, 0) with this `TransformRelation` logged at `parent/child` means
+    /// that from the point of view of `parent`, `parent/child` is translated 1 unit along `parent`'s Y axis.
+    /// From perspective of `parent/child`, the `parent` entity is translated -1 unit along `parent/child`'s Y axis.
+    ParentFromChild(default),
+
+    /// The transform describes how to transform into the child entity's space.
+    ///
+    /// E.g. a translation of (0, 1, 0) with this `TransformRelation` logged at `parent/child` means
+    /// that from the point of view of `parent`, `parent/child` is translated -1 unit along `parent`'s Y axis.
+    /// From perspective of `parent/child`, the `parent` entity is translated 1 unit along `parent/child`'s Y axis.
+    ChildFromParent,
+}

crates/store/re_types/src/archetypes/transform3d_ext.rs

@@ -1,5 +1,5 @@
 use crate::{
-    components::{Scale3D, TransformMat3x3, Translation3D},
+    components::{Scale3D, TransformMat3x3, TransformRelation, Translation3D},
     Rotation3D,
 };
 
@@ -119,11 +119,15 @@ impl Transform3D {
     }
 
     /// Indicate that this transform is from parent to child.
-    /// This is the oppositve of the default, which is from child to parent.
+    ///
+    /// This is the opposite of the default, which is from child to parent.
     #[allow(clippy::wrong_self_convention)]
     #[inline]
-    pub fn from_parent(mut self) -> Self {
-        self.transform = self.transform.from_parent();
-        self
+    #[deprecated(
+        since = "0.18.0",
+        note = "Use `.with_relation(rerun::TransformRelation::ChildFromParent)` instead."
+    )]
+    pub fn from_parent(self) -> Self {
+        self.with_relation(TransformRelation::ChildFromParent)
     }
 }