lighting both side of triangle

Alucard344 · Post by **Alucard344** » Mon Apr 25, 2011 2:22 pm

As the title says, i need to light both side of my mesh. this is because i have clipping plane and when a mesh is cut, i don't want to see the interior of the mesh black.

The only way i see to do that would be to duplicate the mesh with the invert normal. but that would lower the performance.

What would be the best way to achieve that ? Does Irrlicht provide any function or material to help on that ?

Thanks

Klunk · Post by **Klunk** » Mon Apr 25, 2011 2:40 pm

i don't know about any native irrlicht method of doing it, but in a HLSL shader
you can pass

Code: Select all

float  backfacing 	: VFACE;

to the pixel shader, you can then use it in the pixel shader to modulate the normal for example. IIRC its only available to pixelshader 2 or greater.

for GLSL you would check

Code: Select all

gl_FrontFacing

in the fragment

serengeor · Post by **serengeor** » Mon Apr 25, 2011 3:05 pm

Disable backface culling, maybe? Just a guess.

Alucard344 · Post by **Alucard344** » Mon Apr 25, 2011 3:33 pm

I already tried to disable backface culling but it doesnt change anything

Klunk · Post by **Klunk** » Mon Apr 25, 2011 6:45 pm

The only way i see to do that would be to duplicate the mesh with the invert normal. but that would lower the performance.

is that strictly true ? maybe some initial hit if creating the geometry on the fly and some impact from the scene manager having to handle another object but I can't see the drawing performance being much different for a 2 sided material or a 2 sided mesh. Suppose it costs double the verts, which should be quite cheap depending on the complexity of the mesh.

Alucard344 · Post by **Alucard344** » Mon Apr 25, 2011 6:56 pm

well i was really curious as if there was a better solution. maybe it wouldn't decrease a lot the performance even if i do have big complex mesh. I just feel that duplicating all mesh is not the optimal way of doing it.

thanks for your answers.

ent1ty · Post by **ent1ty** » Mon Apr 25, 2011 8:44 pm

The fastest and the simplest way is to use shaders

hybrid · Post by **hybrid** » Mon Apr 25, 2011 10:12 pm

For OpenGL we could add two-sided lighting. But IIRC D3D does not offer this?!

Lonesome Ducky · Post by **Lonesome Ducky** » Tue Apr 26, 2011 4:08 am

If you duplicate the mesh, invert normals, and enable backface culling, it shouldn't be a whole lot more of a performance hit than turning off backface culling on the normal mesh.

ent1ty · Post by **ent1ty** » Tue Apr 26, 2011 8:36 am

hybrid wrote:For OpenGL we could add two-sided lighting. But IIRC D3D does not offer this?!

http://irrlicht.sourceforge.net/phpBB2/ ... 206#238206

Yes please

Alucard344 · Post by **Alucard344** » Tue Apr 26, 2011 5:37 pm

It would be great if it was someday implemented in irrlicht for openGL.
for now im going to go with duplicating the mesh. i think its the simplest solution.

Thanks.