[osg-users] [Problem with osgLight]

[Paul Melis]

Jean-Baptiste Authesserre wrote:
> Sorry for the previous mail. I'm a little confused. My camera is 
> configured to take Y-axis as UP axis. In my 3D-model, I put the helmet 
> so that the bottom of the helmet correspond to negative Y, and the top 
> to positive Y (cf attached figure). The camera look at (0, 0, 0). Thus 
> I can obtain the attached image. To enlight the scene I put the light 
> at 0 on X-axis so the region around the bottom corners of the square 
> be enlighten the same way (the square is in the XY plane). However the 
> region around bottom-left corner is darker than the region around 
> bottom-right corner. What have I missed?
Ah! You said "my object isn't uniformly enlighten" in your original 
mail. With "object" I figured you meant the whole thing/"helmet". I now 
see what you mean w.r.t. the dark corner on the square. Could it be that 
you have an incorrect normal for that corner of the square? Are the 
square and helmet one object? Does it still show when you display only 
the square (i.e. could it be an artifact that actually comes from the 
helmet, and not the square)?

Paul
>
> Jean-Baptiste
>
> 2008/6/18 Jean-Baptiste Authesserre <authesse at gmail.com 
> <mailto:authesse at gmail.com>>:
>
>     Hi,
>
>     I am a little confused. My camera
>
>     2008/6/18 Paul Melis <paul at science.uva.nl
>     <mailto:paul at science.uva.nl>>:
>
>         Jean-Baptiste Authesserre wrote:
>
>             Hi everyone,
>
>             I have some problem with OSG Light, and I don't find
>             answer in the osg archives. My problem is the following :
>             I don't understand why with the following code my object
>             isn't uniformly enlighten. (cf. image in attached document)
>             -The black and white square of the image is centered at
>             (0, 0, 0) (in world frame with convention (x, y, z))
>             -The camera is located at (0, 0, -20)
>             -the light is located at (0,20, -15)
>
>         If you didn't change this yourself then +Z will be the up
>         axis, btw
>
>
>
>             The code for activating light is the following:
>
>             /*****************************
>             ** light *************************************/
>
>
>                //Creation of light source
>                osg::Light* light = new osg::Light();
>                osg::LightSource * lightsource = new osg::LightSource();
>                lightsource->setLight(light);
>                // put the light source in the scenegraph
>                root->addChild(lightsource);
>
>                // turn light on
>                osg::StateSet * stateset = root->getOrCreateStateSet();
>                lightsource->setStateSetModes(*stateset,
>             osg::StateAttribute::ON);
>                light->setAmbient(osg::Vec4d(1.0, 1.0, 1.0, 1.0));
>                //light->setDiffuse(osg::Vec4d(0.0, 0.0, 0.0, 0.0));
>                //light->setSpecular(osg::Vec4d(1.0, 1.0, 1.0, 1.0));
>                light->setPosition(osg::Vec4d(0.0, 20.0, -15.0, 1.0));
>
>             /******************************************************************************/
>
>             So, I don't understand why the bottom-left corner of my
>             square is darker than the others corners
>
>         I don't see any difference here between left and right bottom
>         corners, they're equally dark IMHO. Which seems to make sense,
>         as you've put the light source above and little in front of
>         the camera, but in the center of the object (the X plane).
>
>         Paul
>
>             Has anybody an Idea?
>
>
>             Best regards,
>
>             Jean-Baptiste.
>             ------------------------------------------------------------------------
>
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