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Loki Eliot

Blender question : Double sided Plane

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Im working on a project that has a tree with branches on it. Im useing Blender 2.62.

The branches are simpley a plane with texture shown on both sides. Question is, how to i make blender do this as when i upload to SL only one side of the plane is shown while the otherside is invisible. :-s

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The Second Life rendering engine only renders one side of polygons (the side that the normal vector points out of).  To see this, maneuver your camera inside any object or avatar, and you can see it's invisible from the inside.

I'm not familiar with the solidify function in Blender (I use 3ds Max), but if it turns a plane into a box it is adding extra polygons you don't need around the edge of the box.  What I usually do for plants is copy the leaf planes without moving them, flip the normal vector so it points the other way, and then joining the copy to the original so they are both part of the model.

For most objects, rendering only one side saves work for the graphics engine, but there are a few like plant leaves and windows where you need to double the geometry so it can be seen from both sides.  Some graphics engines have a setting per material for "2-sided" so you don't have to double the geometry, but the SL viewer does not have that feature.

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What Daniel is explaining: Well, you don't get any extra verts but more faces around the edge which would be very small and useless. To make a two sided plane, (it will still have 8 verts no matter what using solidify or copy face.)

Blender, have plane: select - SHIFT + D to copy (click out so it doesnt move), W , choose  flip normals.

Two planes in the same place with opposing normals.

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Daniel's method works, but in Blender the Solidify modifier is preferable because it is non-destructive. To avoid adding extra polygons around the edges, uncheck the "Fill Rim" option.

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If you're really sneaky, you can add just one more vert.

 

Make a plane> Select one vert > Shift D and move the vert down > select all the verts, except the one you first copied > Fill should auto fill in the faces. It might even get the normals correct, if you're really lucky.

 

I think the poly count winds up being the same, but it does save 3 verts. Although.. If you plan on baking textures to your model in blender, something about the super pointyness of the closed end drives the renderer bonkers. But, so will baking textures to two interpolated planes with flipped normals. Pick yer poison. =P (keep planes with flipped normals a reasonable distance apart while baking tex to avoid bonkerness)

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That method works only with fullbright faces. Flat shading requires all the vertex normals to be orthogonal to the faces between them. If three of the vertices are shared between two surfaces facing opposite directions, their normals will be shared as well, and that will totally mess up the shading at those connected corners.

You can "fix" the problem by forcing flat shading in Blender, but then you will end up with 8 physical vertices anyway because Blender will split the surface.

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Thanks! I'd never really thought about why the render goes bonkers in those situations. I guess i chalked it up to closeness of the faces. Wonky normals does make a Lot of sence. Thanks for explaining it!

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