The interaction of ultra-intense femtosecond lasers with plasmas is of interest for a variety of applications, including the acceleration of ultra-short, highly energetic electron bunches and the realization of compact secondary radiation sources. In all these scenarios, radiative processes are either a powerful diagnostic tool or the main physical process at play, and it is therefore very important to simulate them accurately in order to effectively design experiments and interpret their results.In this contribution we describe the implementation of a radiation module in the open-source, massively parallel, Particle-In-Cell code WarpX. We provide benchmarks of this module on different architectures, including AMD GPUs, NVIDIA GPUs, and various CPUs. We also discuss how large-scale simulations performed with this radiation module can be used to support the experimental investigation of a novel injector concept for a laser-driven electron accelerator.The WarpX code is a highly-parallel and highly-optimized code, which can run on GPUs and multi-core CPUs. WarpX is used on the world’s largest supercomputers (including Frontier, Fugaku and LUMI), and was awarded the 2022 ACM Gordon Bell Prize. WarpX has recently become a project of the High-Performance Software foundation.