Interoperation

To integrate the dojox.gfx2d and dojox.gfx3d, we are going to derive dojox.gfx3d.Viewport from dojox.gfx2d.Shape, in another word, Viewport is regarded as yet another 2D shape. This may sound ridiculous, but logically, the 3D space is a 2D canvas with a rich set of command, just as dojox.gfx2d.Path is; pragmatically, this enable users to aggregate more than one Viewport into Surface, a good candidate for subgraphic¹⁰.