Some relation line cases can be optimized, including:

• 1. merge function 1d, when merged layer is open.
• 2. concatenate3d miss one relation line when layer is open.
• 3. merge2d function and merged3d function, use curve line when layer is open, make sure the relation line will not overlap.
• 4. functional model's relation line, the relation line from last layer is curve now, which should be straight line.