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(For more resources on the subject, see here.)
You can download the finished creature by clicking here.
Retopologizing for games
Okay, we’ve got our high-poly mesh ready. But in order to bring it into a game engine, we need to build a low-polygon mesh from it. Because we used ZSketch in the beginning, we now create the low-poly mesh at the end of the process. This step is called retopologizing, or in most cases just retopo, because it creates a mesh with a new topology and projects the details from the high-poly onto it. In this way, we end up with a mesh with a clean and optimized topology and all of the high resolution details that we sculpted in earlier.
This process can also be done in other major 3D applications such as Blender, 3ds Max, and so on. Honestly, I would prefer the retopologizing in Blender over that of ZBrush, as I find it a bit more robust. Nonetheless, the results are the same. So let’s see how we can do this in ZBrush
Before retopologizing, we should be clear about these points:
- Polycount: Think of how many polygons the character should have; this always seems tricky, but after some time you get used to it. Ask yourself how many polygons your platform and engine can handle for a character and how big will it be seen onscreen. Let’s say our Brute will be used on a PC and console title, he’s a few meters high and is visible fullscreen. So we’re heading roughly for something around 5000 polygons. This is a very rough estimate and if we need less polygons for it, that’s fine too. The fewer the better.
- Animation: How will the character be animated? If there’s elaborate facial animation going on, the character should have enough polygons in his face, so the animator can move something. Ideally, the polygon-flow supports the animation.
- Quads: Always try to establish as many quads as possible. Sometimes, we just need to add triangles, but try to go for quads wherever you can.
With these three points in mind, let’s start retopologizing
Time for action – creating an in-game mesh with retopologize
- First, lower the subdivision levels of all the subtools to get increased performance.
- Append a ZSphere as a subtool and make it the active one.
- Name it something meaningful like Retopo.
- Activate Transparency and place the ZSphere inside the mesh so that it is hidden, as shown in the next screenshot. Appending a ZSphere to the model gives us the advantage to easily hide subtools or adjust their subdivision level as we need it:
- Deactivate Transparency and go to Tool Topology| and click on Edit Topology.
- Activate Symmetry.
- Pick the SkinShade4 material and choose a darker color, so that we can see the orange lines of the retopologizing better. The SkinShade4 material offers very low contrast, which is what we need here.
- Begin drawing edges by left-clicking on the mesh. They will automatically snap to the underlying high-poly surface. Start out by laying in two circles around the eyes, as explained in the next image
When in retopologize mode, left-clicking adds a new vertex and an edge connecting it to the last selected vertex. If we want to start out from a different vertex, we can select a new starting point by Ctrl + left-clicking. Deleting points can be done by Alt + left-clicking. When you miss the point you wanted to delete, the last selected one gets deleted instead, so be careful about that.