Constraint: Geometry Attribute

Add a new constraint called "Geometry Attribute", which directly
samples vector, quaternion, or 4x4 matrix attributes from geometry and
applies these to an object's or bone's transform.

This can be used to transfer data generated by geometry nodes to the
object or bone level. By default the constraint will sample a vector
on the vertex domain. The default attribute is `position` for
simplicity, but the attribute value does not have to have anything to
do with neither the transform of the geometry object nor the geometry
itself.

Pull Request: https://projects.blender.org/blender/blender/pulls/136477

scripts/startup/bl_ui/properties_constraint.py

@@ -977,8 +977,35 @@ class ConstraintButtonsPanel:
 
         self.draw_influence(layout, con)
 
+    def draw_geometry_attribute(self, context):
+        layout = self.layout
+        con = self.get_constraint(context)
+        layout.use_property_split = True
+        layout.use_property_decorate = True
+
+        self.target_template(layout, con, False)
+        layout.prop(con, "apply_target_transform", text="Offset with Target Transform")
+
+        layout.prop(con, "attribute_name", text="Attribute Name")
+        layout.prop(con, "data_type", text="Data Type")
+        layout.prop(con, "domain", text="Domain")
+        layout.prop(con, "sample_index", text="Sample Index")
+
+        layout.separator()
+        layout.prop(con, "mix_mode", text="Mix Mode", text_ctxt=i18n_contexts.constraint)
+
+        if con.data_type == 'FLOAT4X4':
+            row = layout.row(heading="Enabled")
+            row.prop(con, "mix_loc", text="Location", toggle=True)
+            row.prop(con, "mix_rot", text="Rotation", toggle=True)
+            row.prop(con, "mix_scl", text="Scale", toggle=True)
+            row.label(icon='BLANK1')
+
+        self.draw_influence(layout, con)
 
 # Parent class for constraint sub-panels.
+
+
 class ConstraintButtonsSubPanel:
     bl_space_type = 'PROPERTIES'
     bl_region_type = 'WINDOW'
@@ -1664,6 +1691,18 @@ class BONE_PT_bKinematicConstraint(BoneConstraintPanel, ConstraintButtonsPanel,
     def draw(self, context):
         self.draw_kinematic(context)
 
+ # Geometry Attribute Constraint.
+
+
+class OBJECT_PT_bGeometryAttributeConstraint(ObjectConstraintPanel, ConstraintButtonsPanel, Panel):
+    def draw(self, context):
+        self.draw_geometry_attribute(context)
+
+
+class BONE_PT_bGeometryAttributeConstraint(BoneConstraintPanel, ConstraintButtonsPanel, Panel):
+    def draw(self, context):
+        self.draw_geometry_attribute(context)
+
 
 classes = (
     # Object Panels
@@ -1704,6 +1743,8 @@ classes = (
     OBJECT_PT_bTransformCacheConstraint_layers,
     OBJECT_PT_bArmatureConstraint,
     OBJECT_PT_bArmatureConstraint_bones,
+    OBJECT_PT_bGeometryAttributeConstraint,
+
     # Bone panels
     BONE_PT_bChildOfConstraint,
     BONE_PT_bTrackToConstraint,
@@ -1743,6 +1784,7 @@ classes = (
     BONE_PT_bTransformCacheConstraint_layers,
     BONE_PT_bArmatureConstraint,
     BONE_PT_bArmatureConstraint_bones,
+    BONE_PT_bGeometryAttributeConstraint,
 )
 
 if __name__ == "__main__":  # only for live edit.