#1153 New arc from 3 points command for 2D CAD

src/blenderbim/blenderbim/bim/module/cad/__init__.py

@@ -21,6 +21,7 @@ from . import operator, workspace
 
 classes = (
     operator.CadArcFrom2Points,
+    operator.CadArcFrom3Points,
     operator.CadFillet,
     operator.CadMitre,
     operator.CadTrimExtend,

src/blenderbim/blenderbim/bim/module/cad/operator.py

@@ -140,8 +140,9 @@ class CadFillet(bpy.types.Operator):
             layout.prop(self, prop)
 
     def execute(self, context):
-        if bpy.context.mode != "EDIT_MESH":
-            return {"CANCELLED"}
+        bpy.ops.object.mode_set(mode="OBJECT")
+        bpy.ops.object.mode_set(mode="EDIT")
+
         obj = bpy.context.active_object
         cursor = obj.matrix_world.inverted() @ bpy.context.scene.cursor.location
         mesh = obj.data
@@ -205,6 +206,7 @@ class CadFillet(bpy.types.Operator):
 
         bmesh.update_edit_mesh(mesh)
         mesh.update()
+        bm.free()
         return {"FINISHED"}
 
 
@@ -212,7 +214,6 @@ class CadArcFrom2Points(bpy.types.Operator):
     bl_idname = "bim.cad_arc_from_2_points"
     bl_label = "CAD Arc from 2 Points"
     bl_options = {"REGISTER", "UNDO"}
-
     resolution: bpy.props.IntProperty(name="Arc Resolution", min=1, default=1)
     should_flip: bpy.props.BoolProperty(name="Flip", description="Flip arc", default=False)
 
@@ -254,4 +255,81 @@ class CadArcFrom2Points(bpy.types.Operator):
         bmesh.ops.spin(bm, geom=[v], axis=axis, cent=cursor, steps=self.resolution * 4, angle=-angle)
         bmesh.update_edit_mesh(mesh)
         mesh.update()
+        bm.free()
+        return {"FINISHED"}
+
+
+class CadArcFrom3Points(bpy.types.Operator):
+    bl_idname = "bim.cad_arc_from_3_points"
+    bl_label = "CAD Arc from 3 Points"
+    bl_options = {"REGISTER", "UNDO"}
+    resolution: bpy.props.IntProperty(name="Arc Resolution", min=1, default=1)
+    only_recalculate_center: bpy.props.BoolProperty(name="Only Recalculate Center", default=False)
+
+    @classmethod
+    def poll(cls, context):
+        obj = context.active_object
+        return obj and obj.type == "MESH" and context.mode == "EDIT_MESH"
+
+    def draw(self, context):
+        layout = self.layout
+        for prop in self.__class__.__annotations__.keys():
+            layout.prop(self, prop)
+
+    def execute(self, context):
+        bpy.ops.object.mode_set(mode="OBJECT")
+        bpy.ops.object.mode_set(mode="EDIT")
+
+        if bpy.context.mode != "EDIT_MESH":
+            return {"CANCELLED"}
+
+        obj = bpy.context.edit_object
+        mesh = obj.data
+        bm = bmesh.from_edit_mesh(mesh)
+
+        selected_verts = [v for v in bm.verts if v.select]
+        if len(selected_verts) != 3:
+            return {"CANCELLED"}
+        pts = [v.co for v in selected_verts]
+        center = tool.Cad.generate_3PT(pts, obj, self.resolution * 4)
+        if not center:
+            return {"CANCELLED"}
+
+        bpy.context.scene.cursor.location = center
+        if self.only_recalculate_center:
+            bm.free()
+            return {"FINISHED"}
+
+        def get_distance_to_other_points(vert):
+            other_verts = [v for v in selected_verts if v != vert]
+            total_vector = mathutils.Vector((0, 0, 0))
+            for other_vert in other_verts:
+                total_vector += other_vert.co - vert.co
+            return total_vector.length
+
+        # For three selected points that represent a start, end, and point on an
+        # arc, the start and end verts can be identified by being furthest away
+        # from the other 2 points.
+        arc_end_verts = sorted(selected_verts, key=get_distance_to_other_points)[-2:]
+        normal = mathutils.geometry.normal(pts)
+
+        dir1 = (arc_end_verts[0].co - center).normalized()
+        dir2 = (arc_end_verts[1].co - center).normalized()
+
+        # Let's get the matrix that represents the coordinate system of the arc.
+        # This matrix allows us to get 2D vectors for calculating the signed arc angle.
+        z = normal
+        x = (arc_end_verts[0].co - center).normalized()
+        y = z.cross(x)
+        arc_matrix = mathutils.Matrix([x, y, z]).transposed().to_4x4()
+
+        dir1 = ((arc_matrix.inverted() @ arc_end_verts[0].co) - (arc_matrix.inverted() @ center)).normalized()
+        dir2 = ((arc_matrix.inverted() @ arc_end_verts[1].co) - (arc_matrix.inverted() @ center)).normalized()
+        angle = dir1.xy.angle_signed(dir2.xy)
+
+        v = arc_end_verts[0]
+        bmesh.ops.spin(bm, geom=[v], axis=normal, cent=center, steps=self.resolution * 4, angle=-angle)
+        bmesh.update_edit_mesh(mesh)
+        mesh.update()
+        bm.free()
         return {"FINISHED"}

src/blenderbim/blenderbim/bim/module/cad/workspace.py

@@ -41,6 +41,7 @@ class CadTool(WorkSpaceTool):
         # Enable Mesh Tools add-on to get this amazing tool
         ("mesh.offset_edges", {"type": "O", "value": "PRESS", "shift": True}, {"properties": []}),
         ("bim.cad_arc_from_2_points", {"type": "C", "value": "PRESS", "shift": True}, {"properties": []}),
+        ("bim.cad_arc_from_3_points", {"type": "V", "value": "PRESS", "shift": True}, {"properties": []}),
     )
 
     def draw_settings(context, layout, tool):
@@ -64,6 +65,10 @@ class CadTool(WorkSpaceTool):
         row.label(text="", icon="EVENT_SHIFT")
         row.label(text="2-Point Arc", icon="EVENT_C")
 
+        row = layout.row(align=True)
+        row.label(text="", icon="EVENT_SHIFT")
+        row.label(text="3-Point Arc", icon="EVENT_V")
+
 
 class CadHotkey(bpy.types.Operator):
     bl_idname = "bim.cad_hotkey"

src/blenderbim/blenderbim/tool/cad.py

@@ -25,12 +25,15 @@
 #
 #  - Instead of AutoVTX, user explicitly chooses V, T, or X mode
 #  - Instead of adding edges, existing edges are extended
+#  - An arc is reconstructed from 3 points instead of a full circle
+#  - You can now derive the center from an arc without generating geometry
 
 
 import sys
 import bpy
+import math
 import bmesh
-from mathutils import Vector, geometry
+from mathutils import Vector, Matrix, geometry
 from mathutils.geometry import intersect_line_line as LineIntersect
 from mathutils.geometry import intersect_point_line as PtLineIntersect
 
@@ -298,3 +301,30 @@ class Cad:
         elif mode == "V":
             bm = cls.perform_v(bm, point, edges[0], edges[1], (p1, p2, p3, p4), vertex_indices)
         return bm
+
+    @classmethod
+    def generate_3PT(cls, pts, obj, nv, mode=1):
+        mw = obj.matrix_world
+        V = Vector
+        nv = max(3, nv)
+
+        # construction
+        v1, v2, v3, v4 = V(pts[0]), V(pts[1]), V(pts[1]), V(pts[2])
+        edge1_mid = v1.lerp(v2, 0.5)
+        edge2_mid = v3.lerp(v4, 0.5)
+        axis = geometry.normal(v1, v2, v4)
+        mat_rot = Matrix.Rotation(math.radians(90.0), 4, axis)
+
+        # triangle edges
+        v1_ = ((v1 - edge1_mid) @ mat_rot) + edge1_mid
+        v2_ = ((v2 - edge1_mid) @ mat_rot) + edge1_mid
+        v3_ = ((v3 - edge2_mid) @ mat_rot) + edge2_mid
+        v4_ = ((v4 - edge2_mid) @ mat_rot) + edge2_mid
+
+        r = geometry.intersect_line_line(v1_, v2_, v3_, v4_)
+        if r:
+            p1, _ = r
+            cp = mw @ p1
+            return cp
+        else:
+            print("not on a circle")