Ray trees are evaluated to render an image in a computer graphic program with a shaded object by launching rays from an object to be shaded in a scene. The rays intersect other objects in the scene at hit points. The hit points that can be shaded by the same shader program are assigned to the same computational group referred to as a shading grid. The hit points in the same shading grid are evaluated by operators in the shader program as a group. The image may then be rendered using the evaluated hit points.