: Add Boolean operations for 3D models, include model merging, subtracting and intersecting operations.
Note：This function works for two models only.
Figure 1: The Boolean Option.
Union refers to the merging of selected models.
Figure 2: Enabled "Union".
Figure 3: Disabled "Union".
Figure 4: Enabled "Union".
Figure 5: Disabled "Union".
Subtract (A-B) will remove the last selected model from the first selected model.
Figure 6: Enabled "Subtract (A-B)".
Figure 7: Disabled "Subtract (A-B) ".
Subtract (B-A) will remove the first selected model from the last selected model.
Figure 8: Enabled "Subtract (B-A)".
Figure 9: Disabled "Subtract (B-A)".
Intersect will keep the overlapped region between the selected models.
Figure 10: Enabled "Intersect".
Figure 11: Disabled "Intersect".
