A fragment shader and method of operation are provided for a hybrid ray tracing system. The method includes determining whether a fragment is to be rasterized or raytraced. If a determination is made that the fragment is to be rasterized, a predetermined value for the fragment is stored into a rasterization target, the predetermined value indicating that the fragment is to be excluded from raytracing operations. If a determination is made that the fragment is to be raytraced, a primitive identifier of the fragment is stored into a rasterization target.