In today's Cinema 4D quick tip, I'm going to show you how to apply a separate
decal map to the front and the back of your 3D objects. The key to that is the
side attribute in the Cinema 4D Texture tag. Before we get into that,
though, we need to have a short discussion about normals. 3D objects,
as you probably know, are made up of rectangles and triangles that we call
polygons, and each of these polygons has a direction. It has a front and a back,
and that direction is indicated by the polygon normal. You can see the normal by
going to the Options menu of the viewport and enabling the Polygon Normals option.
You'll see these little white sticks coming out of the middle of each of the
polygons. So when the stick is facing towards you, you're seeing the front of
the polygon. If we reverse the normals, now we're seeing the back. And you can
also see that there's a different shading, even without the sticks visible when
you're looking at the back of the polygons. You're actually going to get a
bluish shading in the viewport. However, this shading doesn't work if you're under
a subdivision surface object, and I find it a little bit harder to distinguish in
the viewport. So I like to simply use the sticks to make it very clear.
So now that we understand normals, let's talk about the side attribute.
When the side attribute is set to Both, the texture is projected on both the front
and the back of the polygon. When the side attribute is set to Front,
it's only projected on the front of the polygon. If I reverse these normals,
you'll see that we don't get the texture anymore. But if I set the side to Back,
now we will see the texture, because now the texture is projected on the backside
of the polygon. So the normals and the side attribute are very closely related.
Typically, you're going to want to make sure that your normals are facing towards
the camera, and that your side attribute is set to either Both or Front.
With decal mapping, it's really handy to use the front side, because the flat as
well as the spacial projection have a little bit of a special trick when it
comes to the front side. That is that the texture will only be projected when the
Z-axis of the texture is facing the normal. So here, with this texture we have
here, if we activate the Texture Axis mode, you'll see that the Z-axis is facing
towards the front of the tube. The normals we already know are coming out of the
front of the tube. So the Z-axis and the normal are pointing at each other,
and we see the texture on the front of the tube. If we roll around to the back here,
you might get a little confused because we see the texture here as well.
That's just because the OpenGL viewport doesn't support the side attribute.
If I render this, you'll see that we're not getting the texture here,
because in this case the Z-axis of the texture is pointing in the same direction
as the normal on the back of the tube. So now we can use this to our advantage.
We can apply an additional Texture tag as a decal map. You'll notice that I've
already rotated this Texture tag so that the Z-axis is facing towards the back of
the tube. Now if I render, I get the decal map that should be applied on the
back, on the back. If I roll around here, you'll see that we still get the decal map
that should be on the front, on the front. Now, one more little thing to be aware of
is that I have made my tube editable and pulled it out of the hierarchy in order to
illustrate this to you. But our tube actually came as a Loft Nurbs,
and the normals for Loft, Delayed, and other Spline objects are based on the
direction of the Spline. Unfortunately, there's no real way to see the normals.
Of course, you will notice if you apply textures onto the front side of the
object and you're not seeing those textures. The way to solve that is to
simply toggle this Flip Normals option that's in all of the Spline objects.
So here, with Flip Normals off, you can see that we're actually not getting any of
the texture. All the textures are being applied on the inside of the tube.
But if I enable Flip Normals, the normals are facing the correct direction and we
get the textures that we want. So that's how to apply decal maps on the front and
back, and really control your decal mapping based on the normals
as well as the side attribute in your Texture tag. If you enjoyed this quick
tip, please like, share, and visit cineversity.com for more great
Cinema 4D tutorials and resources.