Counting Feynman-like graphs: Quasimodularity and Siegel-Veech weight

We prove the quasimodularity of generating functions for counting torus covers, with and without Siegel-Veech weight. Our proof is based on analyzing decompositions of flat surfaces into horizontal cylinders. The quasimodularity arise as contour integral of quasi-elliptic functions. It provides an alternative proof of the quasimodularity results of Bloch-Okounkov, Eskin-Okounkov and Chen-Moeller-Zagier, and generalizes the results of Boehm-Bringmann-Buchholz-Markwig for simple ramification covers.