[PD] texturing a circular image onto a hemisphere in GEM

Alex x37v.alex at gmail.com
Wed Oct 17 23:08:56 CEST 2007


I started trying to draw a hemisphere with the appropriate texturing
coordinates using GEMgl commands, but that was getting too complicated
so I copied the sphere object source, made it draw a hemisphere, and
changed how it does texturing... I'll share it once I get all of the
kinks ironed out.

-Alex

On 10/17/07, marius schebella <marius.schebella at gmail.com> wrote:
> hmm... no, I don't know how to do it. with gem you can only do
> rectangular projection/texturing. so you would have to find a way to
> distort the texture so that it will be displayed correctly on one half
> of the sphere. you probably need some vertex shader to do that...
> marius.
>
>
> Alex wrote:
> > so to make this easy think of a square texture that has a picture the
> > globe centered inside it.
> > i want to take that picture and map the flat image of the globe onto a
> > hemisphere so that you see [in this virtual world] 1/2 of a globe,
> > warped so that, in the virtual world, it looks correct.
> >
> > -Alex
> >
> > On 10/15/07, marius schebella <marius.schebella at gmail.com> wrote:
> >> Hi alex,
> >> I am not sure what you're trying to do, but I am eager to help you...
> >> do you want to project the video onto a wall/ceiling hemisphere inside a
> >> real room? or are you talking about virtual projections?
> >> I guess what you have to do first is distort the circled video back into
> >> a square and then use that to texture the sphere.
> >> marius.
> >>
> >>
> >> sphere with a ? is it just the mapping on the spherefor any distortion you
> >>
> >> Alex wrote:
> >>> Maybe a different subject will inspire some help?
> >>>
> >>> basically, I have video that was shot on a mirrored spherical ball..
> >>> this gives a circular image inside a rectangular video, I've figured
> >>> out how to crop it so that I just get the square that surrounds the
> >>> circle, but I cannot figure out how to correctly map this texture onto
> >>> a sphere so that it is only on one hemisphere and so that the circle's
> >>> circumference is on a "great circle" of the sphere? [ie it the circle
> >>> is warped out so that it becomes a hemisphere].
> >>>
> >>> I figure maybe I have to do some GEMgl stuff for this?
> >>>
> >>> if anyone has done this, would you please share?
> >>>
> >>> If not, any advice?
> >>>
> >>> Thanks,
> >>> -Alex
> >>>
> >>>
> >>> On 10/10/07, Alex <x37v.alex at gmail.com> wrote:
> >>>> I have some panoramic video that I want to use to texture a hemisphere
> >>>> [or rather, the bottom half of a sphere].
> >>>>
> >>>> I cannot simply texture the sphere with the video because the warping
> >>>> is not correct.. it seems that I need some sort of non-rectangular
> >>>> warping of the image before I texture the object, or a non-rectangular
> >>>> mapping of the texture onto the sphere.
> >>>>
> >>>> Any ideas or advice?  Does anyone else have experience working with
> >>>> panoramic video in Gem?
> >>>>
> >>>> -Alex
> >>>>
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> >>
> >
>
>




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