If you need to retopologize your model for lower poly counts, or for animation etc, there are several ways to do so. In this tutorial we will look at how to manually retopologise a mesh by starting with a Zsphere base in a new subtool.
Note that as well as being used to retopologise entire models, this technique can be used to create pieces of armour or costume details on top of your existing model.
1: Have your high poly finished mesh open in Zbrush.
2: Go to the Subtools Palette, click Append to add a new Subtool, and from the Pop up menu choose a new Zsphere.
3: Make sure the Zsphere is the active subtool, then scroll down to the Topology palette and click ‘Edit Topology’.
4: The goal now is to draw a new set of polygons, one vertex at a time until the model is covered. Your objective may be to create better edgeflow for animation, or to simply lower the polycount for exporting. Make sure your draw size is small for accuracy, then just start clicking on the model. You can automatically topologise on top of any subtool in the mesh.
5: Different keys do different things. Make sure you are in Draw mode. When you left click, your new vertex will usually just connect to the last. An orange line will appear between verts, forming a grid as you develop your topology. You can go back to other parts of the model by Ctrl + Clicking on a placed vert to start working out from.
Left Click : Place new vertex on mesh, or connect one vertex to another.
Ctrl + Click : Choose which vert you want newly placed verts to connect to
Alt + Click : Remove created Points.
6: If you have misplaced or misaligned verts, you can switch to Move mode and reposition them.
7: Continue working in this way until your new poly mesh is complete.
MAKE UNIFIED SKIN
1: Preview the New Mesh With ‘A‘ (It will be in the zsphere subtool beneath the main tool, so switch off it’s visibility in the Subtools palette). This is what our new topology looks like, but it is still just part of the ZSphere.
2:Scroll down to the Adaptive Skin Palette, and click ‘Make adaptive Skin’. Your new mesh will be saved as a new tool. This can then be appended in as a new subtool for the model, ready to be edited. The original editable Zsphere subtool will still exist too.
Note that in the Adaptive skin rollout we can increase the density slider – this smoothly divides each poly we draw after switching on Adaptive skin mode, meaning we can draw a very low density topology, and still get a fairly decent, accurate looking result.
PROJECTING DETAIL ONTO THE NEW TOPOLOGY
Should you wish, you can actually increase the subdivision level of your new topology to increase the resolution, and then project colour and sculpt detail data from your original mesh back onto the new one!
Note that if the density setting of your Adaptive Skin was high enough, you might not need to subdivide, but you may wish to do the two processes separately.
1: Make sure the new mesh is selected, and the Original mesh is visible.
2:Scroll down to the bottom of the subtool palette and click Project all. You may be asked if you want to project polypaint data, so choose as necessary.
3: The quality of the projection is entirely dependant on the resolution of the new mesh. You can also continue to sculpt on the new mesh if adjustments are necessary.
The topology brush is another older method of generating topology, but depending on your mesh it can be a little bit quicker than the ZSphere method.
Simply select the topology brush and start drawing on top of your mesh. Note that it cannot be used on subdivided model.
Draw lines on the model with Left mouse drag, when they criss-cross, polys are formed.
You can draw loops around limbs etc by starting a line around it and pressing shift. With shift held, moving the mouse will adjust the tilt of the loop to suit your required edgeflow.
Holding Space will allow you to slide the active loop along the limb to adjust its position.
Vertexes appear where lines cross – indicated by green circles.
Alt and draw over the loose strands at the ends of lines to remove them.
To get smother lines, activate Lazy Mouse via Stroke > Lazy Mouse in the taskbar.
Topology appears as a shell on top of model – set brush draw size to 1 for paper thin topology, or thicker to have it stick out from the surface.
The new topology is saved in the same tool as the parent mesh, but if we want to separate it into a new subtool we can:
1: Ctrl + Shift +Left Click on the jeans mesh to hide everything else (i.e the new topology)
2: In the subtools palette click ‘Split Hidden‘. This will put the new geometry into its own subtool.