Move prime tower area generation to separate function

This function is named as if it could later include other printed pieces, but it is meant to only include pieces that have normal bed adhesion, so not the prime locations.

Contributes to issue CURA-2625.

cura/BuildVolume.py

@@ -433,32 +433,18 @@ class BuildVolume(SceneNode):
 
         # Add prime tower location as disallowed area.
         prime_tower_collision = False
-        if ExtruderManager.getInstance().getResolveOrValue("prime_tower_enable") == True:
-            prime_tower_size = self._global_container_stack.getProperty("prime_tower_size", "value")
-            prime_tower_x = self._global_container_stack.getProperty("prime_tower_position_x", "value") - machine_width / 2
-            prime_tower_y = - self._global_container_stack.getProperty("prime_tower_position_y", "value") + machine_depth / 2
-
-            prime_tower_area = Polygon([
-                [prime_tower_x - prime_tower_size, prime_tower_y - prime_tower_size],
-                [prime_tower_x, prime_tower_y - prime_tower_size],
-                [prime_tower_x, prime_tower_y],
-                [prime_tower_x - prime_tower_size, prime_tower_y],
-            ])
-            # Using Minkowski of 0 fixes the prime tower area so it's rendered correctly
-            prime_tower_area = prime_tower_area.getMinkowskiHull(Polygon.approximatedCircle(0))
-
-            #Check if the prime tower area intersects with any of the other areas.
-            #If this is the case, add it to the error area's so it can be drawn in red.
-            #If not, add it back to disallowed area's, so it's rendered as normal.
+        prime_tower_areas = self._computeDisallowedAreasPrinted()
+        for prime_tower_area in prime_tower_areas:
             for area in result_areas:
                 if prime_tower_area.intersectsPolygon(area) is not None:
                     prime_tower_collision = True
                     break
-
-            if not prime_tower_collision:
-                result_areas.append(prime_tower_area)
-            else:
-                self._error_areas.append(prime_tower_area)
+            if prime_tower_collision: #Already found a collision.
+                break
+        if not prime_tower_collision:
+            result_areas.extend(prime_tower_areas)
+        else:
+            self._error_areas.extend(prime_tower_areas)
 
         # The buildplate has errors if either prime tower or prime has a colission.
         self._has_errors = prime_tower_collision or prime_collision
@@ -473,6 +459,23 @@ class BuildVolume(SceneNode):
     #   \return A list of polygons that represent the disallowed areas.
     def _computeDisallowedAreasPrinted(self):
         result = []
+        #Currently, the only normally printed object is the prime tower.
+        if ExtruderManager.getInstance().getResolveOrValue("prime_tower_enable") == True:
+            prime_tower_size = self._global_container_stack.getProperty("prime_tower_size", "value")
+            machine_width = self._global_container_stack.getProperty("machine_width", "value")
+            machine_depth = self._global_container_stack.getProperty("machine_depth", "value")
+            prime_tower_x = self._global_container_stack.getProperty("prime_tower_position_x", "value") - machine_width / 2
+            prime_tower_y = - self._global_container_stack.getProperty("prime_tower_position_y", "value") + machine_depth / 2
+
+            prime_tower_area = Polygon([
+                [prime_tower_x - prime_tower_size, prime_tower_y - prime_tower_size],
+                [prime_tower_x, prime_tower_y - prime_tower_size],
+                [prime_tower_x, prime_tower_y],
+                [prime_tower_x - prime_tower_size, prime_tower_y],
+            ])
+            result.append(prime_tower_area)
+
+        return result
 
     ##  Computes the disallowed areas that are statically placed in the machine.
     #