[Papervision3D] Half Sphere - Primitives and Ideas

[Peter Kapelyan]

Wow that sounds very intense.
However in my mind it seems easy that the texture is tiled (I guess it's
not?).
So if the texture was tiled, and you can move it on x/y then it seems like
it might be possible.
Just some thoughts so I am glad if you can shoot them down!
Because I don't want to be thinking crazy thoughts :)
Thank you Alex

-Peter


On 4/21/07, Alexander Zadorozhny <alexander.zadorozhny at gmail.com> wrote:
>
> Hi Peter!
>
> > THis is ultra cool - because half the polygons/information are
> needed!!!!
> As far as I know, polygons that are actually rendered impact
> performance times greater than those that are culled. And it the
> projection of the vertices forming a polygon that is slow, not the
> actual calculation whether polygon is culled (e.g. for a cube removing
> three faces will result in only one point needn't be projected).
> Anyway, removing faces in certain cases may be of use, I think something
> like
> for (var i:int = 0; i < mesh.faces.length; i++)
>   if (mesh.faces[i].v0.z < 0)
>   {
>      mesh.faces[i].splice(i, 1);
>      i++;
>   }
> will do.
>
> More promising idea seems to cull from projection objects, that are
> totally out of rendering area (including those behind the camera).
>
> > If the texture can be scrolled across that HALFSPHERE
> > and it is Pointed at the camera....,
> > instead rotating a regular SPHERE itself....,
> > then effectively would be exactly like rotating a SPHERE!!!!!!!!!!!!!!!!
> The idea is not bad, however it's much more complex than you could
> expect. And the biggest problem is texturing.
>
> Even if we agree that texture on a sphere is always mapped using
> default spherical mapping, the pole of the sphere may correspond to
> the center of the face, and either you have to split this face or
> generate special texture for it. The same way you have to split or
> generate texture for each face on the date-line meridian (where the
> right side of the texture meets the left side). Together with
> UV-coordinates recalculation this can be much more expensive than
> simple good old full-sphere ;)
>
> I thought of something similar to archive "sphere that renders ideally
> on any zoom using minimum triangles required", but finally ended with
> a kind of MultiMesh that is able to substitute high poly mesh with a
> low poly one when far from the camera.
>
> wbr,
> Alexander
>
> On 4/21/07, Peter Kapelyan <flashnine at gmail.com> wrote:
> > Hi all,
> >
> > This message is for Ralph and Tim have some ideas for you, and anyone
> else
> > that may think of something.
> >
> > A few ideas ran through my mind and I wanted to let you know what I have
> > been thinking.
> >
> > Instead of modelling objects in Lightwave(whatever) I wanted to make
> most of
> > my scene out of PV3D Primitives.
> > So as I was thinking of how to do a turtle, I realized I can do the
> shell
> > with a cone, or better yet half-sphere.
> > Feel like making a half sphere Tim? :) ........... :)
> >
> > Now this One idea only works with a HALFSHPERE, but I have another idea
> > also.
> >
> > I realized how a HALFSHPERE can be ultra cool.
> > When you look at a SPHERE, you never see the other side of it, unless
> the
> > material is transparent, and I am talking just one on screen camera for
> now.
> > So in reality, nobody really NEEDS the other side of the sphere for
> > anything!!!
> > If the texture can be scrolled across that HALFSPHERE and it is Pointed
> at
> > the camera...., instead rotating a regular SPHERE itself...., then
> > effectively would be exactly like rotating a SPHERE!!!!!!!!!!!!!!!!
> > THis is ultra cool - because half the polygons/information are
> needed!!!!
> >
> > Ok now that I have calmed down (and figured out a way for some kind of
> > backface culling hopefully) here is my other idea.
> >
> > If there are such things as "faces" to the primitives (for a box 6
> sides...)
> > then can't you just delete a face?
> > This would be ultracool too because imagine a box with one face missing,
> > well, you have a paper bag, or you are looking into a room with one wall
> > missing.
> > Also Imagine a cone with the bottom missing upside down, you now have an
> > icecream cone.
> > Besides all the uses of removing some faces for making objects, I am
> sure
> > with some correct Z calculations the faces on the back can be deleted as
> > well if needed. This probably needs to be done on each object
> individually
> > depending on the material, because say you have the same object with a
> > transparent type material, and you NEED the back faces.
> >
> > Tim, want to make HALFSPHERE :) I guess it's half a sphere - with the
> code
> > for your top/bottom in the middle. :)
> >
> > Ralph, want to make material = cullbackface!!!!!!!! :) ?????????
> > or material ScrollHalfSphere :)
> >
> > You would have to maybe only be able to delete a range of polygons in
> the
> > order they are created, or the final one, maybe make the parameters for
> > deleting faces in the order of creation ( a certain range like 1rst face
> to
> > 5th face), or make it flexible enough for something like dependant on Z
> > order for backface culling unless its done with the material somehow.
> >
> > Hope these crazy ideas make some sense as they could be of much use.
> Haven't
> > spent much time using PV3D - buying Flash CS3 left me broke so I have
> more
> > time to think :)
> >
> > -Pete
> >
>
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