For best results, keep your eye near the central teapot. Direction of rotation is constant throughout.

As the silhouette's true geometry is revealed, the rotation appears to reverse. When the geometry becomes silhouette again, the rotation appears to change direction once more.
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This demo was made during development of True Reverse Perspective (TRP) to illustrate a couple of the fundamental characteristics of TRP, as I observed them.

1) Objects in Reverse Perspective (RP) share a silhouette with objects in Forward Perspective (FP). The two states are interchangeable with the inversion of certain characteristics of either state (like the direction of rotation, the direction of surface-normals (inside vs outside), etc.).

2) Given only a silhouette, objects and clusters can be physically interpreted in different ways, some more likely than others. Our brain will choose the most likely (familiar) and extrapolate, even reverting back to the incorrect assumption after being shown the error.

eg. If we begin with the silhouette, we give the brain a chance to create an internal model of the structure (in familiar Forward Perspective). Then, when we reveal the actual structure (following rules we don't commonly witness) the brain will quickly reassess and resolve the correct geometry and rotation. Finally, upon switching back to the silhouette, our brain will revert to the original (incorrect) interpretation and "see" the structure rotating in Forward Perspective - even though we "know" that the structure is different to our current perception.

The illusion can be broken pretty easily by tracking one of the outer teapots throughout its rotation. But if focus is maintained near the central structure, the illusion is consistent.

It was coded in OpenGL/C++: For a better description of TRP, see the final piece here [ vimeo.com/12518619 ]

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