We give an algorithm to morph between two planar orthogonal drawings of a graph, preserving planarity and orthogonality. The morph uses a quadratic number of steps, where each step is a linear morph (a linear interpolation between two drawings). This is the first algorithm to provide planarity-preserving morphs with well-behaved complexity for a significant class of graph drawings. Our method is to morph until each edge is represented by a sequence of segments, with corresponding segments parallel in the two drawings. Then, in a result of independent interest, we morph such parallel planar orthogonal drawings, preserving edge directions and planarity.

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We give an algorithm to morph between two planar drawings of a graph, preserving planarity, but allowing edges to bend during the course of the morph. The morph uses a polynomial number of elementary steps, where each elementary step is a linear morph that moves each vertex in a straight line at uniform speed. Although there are planarity-preserving morphs that do not require edge bends, it is an open problem to find polynomial-size morphs. We achieve polynomial size at the expense of edge bends.

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