Lighting a surface flipped (inverted) cube

[oholiab]

Hi! Sorry if this is a dupe, I was pretty unsure on how to word it for Google so I've come up with nada.

I have a cube which I want to use as a room, so I have the following code:

Code: Select all

 
scene::IMeshSceneNode *room = smgr->addCubeSceneNode(15.0f, 0, IDFlag_IsSolid, core::vector3df(10,160,30), core::vector3df(0,0,0), core::vector3df(30, 30, 30));
smgr->getMeshManipulator()->flipSurfaces(room->getMesh());
room->setMaterialFlag(video::EMF_LIGHTING, true);
//room->setMaterialFlag(video::EMF_NORMALIZE_NORMALS, true);
//room->setMaterialFlag(video::EMF_BACK_FACE_CULLING, false);
room->setMaterialTexture(0, driver->getTexture("media/texture.jpg"));
room->setTriangleSelector(smgr->createTriangleSelector( room->getMesh(), room ));
 

The commented lines are ones I've tried with and without.

I have an animated light circling round the room, but it's not lighting these inside faces! So I created a duplicate cube but smaller, without the surface flip:

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scene::IMeshSceneNode *room2 = smgr->addCubeSceneNode(15.0f, 0, IDFlag_IsSolid, core::vector3df(10,160,30), core::vector3df(0,0,0), core::vector3df(3, 3, 3));
room2->setMaterialFlag(video::EMF_LIGHTING, true);
room2->setMaterialTexture(0, driver->getTexture("media/texture.jpg"));
room2->setTriangleSelector(smgr->createTriangleSelector( room2->getMesh(), room2 ));
 

Same cube, inside the other cube, with the same texture and center position, but without the faces flipped... And it lights up just fine!

So, for my first question: what have I missed?

Thanks in advance

[mongoose7]

You probably need to have the normals pointing in, that is, towards the light.

[hendu]

Call recalculatenormals after flipsurfaces.

[oholiab]

Ah, I see - so the quantity and directionality of the light on a surface are calculated from its normals? Does this mean that if I were to render both sides of a surface, not only would I need to disable back side culling but I'd also need to add a normal to the reverse surface so it would receive light?

It worked perfectly by the way, thanks so much