Presented in the paper is a tool-path planning algorithm for direction-parallel area milling consisting of three modules: (1) finding the optimal inclination; (2) calculating and storing tool-path elements; and (3) tool-path linking. For the optimal inclination, we suggest an algorithm that selects an inclination by reflecting the shape of the machining area as well as the tool-path interval. We make use of the concept of a monotone chain and the plane-sweep paradigm to calculate the tool-path elements. The concept of a monotone chain brings clarity and tight-time complexity to the proposed algorithm. The tool-path linking problem is modeled as a TPE-Net (tool-path element net) traversing problem. For the two direction-parallel milling topologies, one-way and zigzag, tool-path linking algorithms are proposed. Empirical tests show that the proposed algorithm fulfills its requirements.