3D coat offers a great feature called Auto-retopology which is a very complicated word. It means basically the process of turning a mesh with a high number of polygons into one with a lower number of polygons. The terms for these meshes are high-poly and low-poly mesh. So you could ask: Why not just leave away the high-poly mesh when we need a low-poly mesh in the end? Well, the reason is, that we want to store the details we modelled into the high-poly mesh to the low-poly mesh by adding these to the normalmap of the low-poly. This is called baking the high-poly mesh details to a normalmap.

In this article we create as simple high-poly model: A kind of rock which we created with primitives and sculpting in the Voxel Rroom. We start by adding a cube, very simple:

Cube primitive in 3d Coat

Cube primitive in 3d Coat

Then we use the CutOff-tool do shape the stone like this:

Result of CutOff operations

Result of CutOff operations

To give it a more realistic look-and-feel we use the Build-tool (most of the time with CTRL-key pressed down for inverse operation) and some grunge-brushes to make the stone look a bit old and damaged:

Sculpt in some scratchesand holes

Sculpt in some scratchesand holes

So what do we have now: A nice looking stone-part with about 400.000 triangles – nice, but not useable in any kind of game engine like Unity or whatever. We need to transform this high-poly model into a low-poly version. This can be done with the auto-retopo feature of 3D Coat.

Select the layer of the object in VoxTree and choose the AUTOPO option for per pixel painting:

Autoretopo for Per Pixel Painting

Autoretopo for Per Pixel Painting

In the following dialogs just press Next and OK without changing anything and finally you will receive an UV-mapped low poly model.

When you move into the Paint Room after this for texturing the low poly model, you see both, the low- and the high-poly version. Hide the high-poly model by selecting Hide Voxels in Paint Room:

Hide Voxel in Paint Room

Hide Voxel in Paint Room

Now you see the low-poly version of your model with baked normalmap (texture in a separate layer):

Low poly retopologized model

Low poly retopologized model

The model looks like if it would still have all details of the high-poly model, but this is just faked – sorry: baked;-) The texture of the normalmap lets the model appear as if the details would still exist.

Now we will add a stone-texture to the model. Add a bitmap to the material section like this one:

Rock texture for model

Rock texture for model

Then you select it in the Materials-panel and choose Tiling and set the preview opacity to 5% in the Preview-options of the tool:

Paint with Rock texture /material

Paint with Rock texture /material

Now select a brush, lower the opacity of the Color to about 30% and paint the texture directly onto your model. Turn around your model while painting to see which parts still have no texture on them.

After that the stone looks already finished. The last thing we will do is adding a bit more realism to it: Choose an almost white color for your brush and set the option Pen pressure not dependend on color to less in cavity.

Color for edges (less in cavity)

Color for edges (less in cavity)

When you paint with that option onto your model, the edges will receive the white strokes flat parts :

3D Coat rock-model (low poly) with baked textures

3D Coat rock-model (low poly) with baked textures

Ok, the rendering is not perfect, some parts could be optimized and also the retopology was fully automated, but for a first demonstration of this feature I think the result looks just fine, what do you think?

In the next tutorial I will show you how to optimize the retopology and UV-mapping process to get a great looking model with low polycount so that you can use it even in a mobile environment like an Android or iOS game.

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