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I noticed an interesting optical illusion with the rotating cube vertices example: if you interpret it as rotating one way, it’s an ordinary cube—the back face

I noticed an interesting optical illusion with the rotating cube vertices example: if you interpret it as rotating one way, it’s an ordinary cube—the back face appears smaller because it’s farther away; but if you interpret it as rotating the other way, you see a shape that’s constantly stretching and deforming. This leads me to wonder what a game would look like if all perspective were so inverted, so that the farther away an object is, the larger it appears.

pnp 11y ago
I haven't seen that. I have seen a rotating camera of a castle spire with the Z buffer culling backwards. It looked strange as the castle seemed to be rotating the wrong way. I recall the skybox was rendered properly adding to the illusion. Edit: I realize what I saw is a textured version of what you are describing.
tobr 11y ago
The apparent size of an object changing with distance is not just some random thing that you can change... it's a consequence of geometry. The eye or camera is a point, but the projection plane is a plane, so a ray from the camera through two adjacent points on the plane will keep diverging on the other side of the projection plane, and hit objects that are further and further apart. Another way to think of it is that there's just more stuff far away than close, so all that far away stuff has to look smaller to fit. If you want to change that, you can't have a camera that is a point. That's how parallel projection works; the camera is basically a plane of the same size as the picture plane, so the rays never diverge. What you're suggesting is basically that the camera would be larger than the projection plane. That would cause the rays to converge in a single point some distance away from the camera. You might then just as well think of that point as the camera, and do what pnp wrote, just reverse the z buffer.
corysama 11y ago
Reverse perspective rendering: https://vimeo.com/12518619 https://vimeo.com/12518619
- iamcreasy 11y ago
  Can't even imagine how it would look like with VR.

pnp 11y ago

I haven't seen that. I have seen a rotating camera of a castle spire with the Z buffer culling backwards. It looked strange as the castle seemed to be rotating the wrong way. I recall the skybox was rendered properly adding to the illusion. Edit: I realize what I saw is a textured version of what you are describing.

tobr 11y ago

The apparent size of an object changing with distance is not just some random thing that you can change... it's a consequence of geometry. The eye or camera is a point, but the projection plane is a plane, so a ray from the camera through two adjacent points on the plane will keep diverging on the other side of the projection plane, and hit objects that are further and further apart. Another way to think of it is that there's just more stuff far away than close, so all that far away stuff has to look smaller to fit. If you want to change that, you can't have a camera that is a point. That's how parallel projection works; the camera is basically a plane of the same size as the picture plane, so the rays never diverge. What you're suggesting is basically that the camera would be larger than the projection plane. That would cause the rays to converge in a single point some distance away from the camera. You might then just as well think of that point as the camera, and do what pnp wrote, just reverse the z buffer.

corysama 11y ago

Reverse perspective rendering: https://vimeo.com/12518619 https://vimeo.com/12518619

iamcreasy 11y ago
Can't even imagine how it would look like with VR.