This paper presents a novel approach to anti-aliased ray marching by indirect shading in cube-map space. Our volume renderer firstly performs ray marching on each visible interior pixel of a maximum-resolution-limited cube map, and then resamples (usually up-scales) the cube imposter in viewport space. By this viewport-resolution-independent strategy, developers can improve both ray-marching performance and its quality of anti-aliasing when allowing larger marching strides. Moreover, our solution also covers depth-occlusion anti-aliasing for mixed mesh-volume rendering, cube-map level-of-details (LOD) optimization for a further performance boost, and multiple-volume rendering by leveraging the GPU inline ray tracing. Besides, our implementation is developer-friendly and the performance-quality tradeoff determined by the parameter configuration is easily controllable.