After projection transform, the view volume is fixed (in Direct3D convention, left clip plane at X -1.0, far clip plane at Z 1.0, near clip at Z 0.0) so there should be no need to transform the frustum.

I think I get you. But is it a typo or something? because In your last post you said you did clipping in homogeneous coordinate before perspective divide, namely in clipping coordinate. But clipping coordinate doesn't have fixed view volume which is in NDC(normalized device coordinate).
Thanks, anyway.

After projection transform, the view volume is fixed (in Direct3D convention, left clip plane at X -1.0, far clip plane at Z 1.0, near clip at Z 0.0) so there should be no need to transform the frustum.

Sorry, I think I get you. But is it a typo or something? because In your last post you said you did clipping in homogeneous coordinate before perspective divide, namely in clipping coordinate. But clipping coordinate doesn't have fixed view volume which is in NDC(normalized device coordinate).
Thanks, anyway.