Fix T68964: Measureit Area computation error

The area was wrong when the scale was used because the scale was applied to the area, not to the sides of the are to compute.

measureit/measureit_geometry.py

@@ -605,12 +605,17 @@ def draw_segments(context, myobj, op, region, rv3d):
                     if ms.gltype == 20:  # Area
                         obverts = get_mesh_vertices(myobj)
                         tot = 0
+                        if scene.measureit_scale is True:
+                            ms_scale = scene.measureit_scale_factor
+                        else:
+                            ms_scale = 1.0
+
                         for face in ms.measureit_faces:
                             myvertices = []
                             for v in face.measureit_index:
                                 myvertices.append(v.glidx)
 
-                            area = get_area_and_paint(myvertices, myobj, obverts, region, rv3d, rgba)
+                            area = get_area_and_paint(myvertices, myobj, obverts, region, rv3d, rgba, ms_scale)
                             tot += area
                         # Draw Area number over first face
                         if len(ms.measureit_faces) > 0:
@@ -623,9 +628,6 @@ def draw_segments(context, myobj, op, region, rv3d):
 
                             d1, dn = distance(p1, p2)
                             midpoint3d = interpolate3d(p1, p2, fabs(d1 / 2))
-                            # Scale
-                            if scene.measureit_scale is True:
-                                tot = tot * scene.measureit_scale_factor
 
                             # mult by world scale
                             tot *= scale
@@ -659,7 +661,7 @@ def draw_segments(context, myobj, op, region, rv3d):
 # Get polygon area and paint area
 #
 # ------------------------------------------
-def get_area_and_paint(myvertices, myobj, obverts, region, rv3d, rgba):
+def get_area_and_paint(myvertices, myobj, obverts, region, rv3d, rgba, ms_scale):
     mymesh = myobj.data
     totarea = 0
     if len(myvertices) > 3:
@@ -687,7 +689,7 @@ def get_area_and_paint(myvertices, myobj, obverts, region, rv3d, rgba):
 
             # Area
 
-            area = get_triangle_area(p1, p2, p3)
+            area = get_triangle_area(p1, p2, p3, ms_scale)
 
             totarea += area
     elif len(myvertices) == 3:
@@ -702,7 +704,7 @@ def get_area_and_paint(myvertices, myobj, obverts, region, rv3d, rgba):
         draw_triangle(screen_point_p1, screen_point_p2, screen_point_p3, rgba)
 
         # Area
-        area = get_triangle_area(p1, p2, p3)
+        area = get_triangle_area(p1, p2, p3, ms_scale)
         totarea += area
     else:
         return 0.0
@@ -714,10 +716,15 @@ def get_area_and_paint(myvertices, myobj, obverts, region, rv3d, rgba):
 # Get area using Heron formula
 #
 # ------------------------------------------
-def get_triangle_area(p1, p2, p3):
+def get_triangle_area(p1, p2, p3, scale=1.0):
     d1, dn = distance(p1, p2)
     d2, dn = distance(p2, p3)
     d3, dn = distance(p1, p3)
+
+    d1 *= scale
+    d2 *= scale
+    d3 *= scale
+
     per = (d1 + d2 + d3) / 2.0
     area = sqrt(per * (per - d1) * (per - d2) * (per - d3))
     return area