Stream processing is a computing paradigm enabling the analysis of data streams arriving at high speed from data producers. Its goal is to extract knowledge and complex events by processing streams with high throughput and low latency. To accomplish this goal, Stream Processing Engines (SPEs) try to exploit the parallel processing capabilities provided by modern hardware (usually multi-core CPUs and distributed systems). The exploitation of hardware accelerators, and in particular of FPGAs, is promising because they can maximize parallelism and reduce energy consumption. However, programming FPGAs is a very cumbersome and challenging task requiring a lot of expertise. In this paper, we discuss the seamless integration of FSPX, a prototype system for generating FPGA-based implementations of streaming pipelines, with an existing SPE (WindFlow). Our goal is to integrate these two tools by providing high-level programming interfaces to end users and guaranteeing high performance with efficient hardware utilization.