A graphics processing unit (GPU) includes one or more processor cores adapted to execute a software-implemented shader program, and one or more hardware-implemented ray tracing units (RTU) adapted to traverse an acceleration structure to calculate intersections of rays with bounding volumes and graphics primitives asynchronously with shader operation. The RTU implements traversal logic to traverse the acceleration structure including transformation of rays as needed to account for variations in coordinate space between levels, stack management, and other tasks to relieve burden on the shader, communicating intersections to the shader which then calculates whether the intersection hit a transparent or opaque portion of the object intersected. Thus, one or more processing cores within the GPU perform accelerated ray tracing by offloading aspects of processing to the RTU, which traverses the acceleration structure within which the 3D environment is represented.