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

Jack jack at rybn.org
Thu Oct 18 15:33:52 CEST 2007

I don't know, but it could help you :
It's in french and about world map.


Le 17 oct. 07 à 23:08, Alex a écrit :

> 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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