1. A system comprising: an assembler to execute on a central processing unit (CPU) and, for each image element of a first plurality of image elements to be rendered as part of a digital image: to identify at least one effect applicable to the respective image element; to select a first effect code for the at least one effect from a collection of effect codes; and to automatically generate a graphics processing unit (GPU) program to include the first effect code, the GPU program to apply the at least one effect to the respective image element and to composite the respective image element according to a compositing mode specific to the respective image element; and an interface to communicate the first plurality of image elements, and the GPU programs, from the CPU to a GPU.