// Block 4 of 10 · 8–9 sessions
Topology and retopology
Why “just making the shape” is not enough: will this mesh survive movement?
- Duration
- 2–3 sessions · ~2 h each
- Checkpoint
- Your object from block 3, checked and retopologized: clean mesh exactly where the movement will be.
- Challenge
- The same model with a deliberately reduced polygon budget (LOD thinking).
#The idea of the block
The “done or not” judgment was purely visual so far: it looks as intended — so it’s done. Block 4 introduces a second criterion, invisible in a screenshot: will this mesh survive movement? A model can look perfect and yet break as soon as someone tries to bend it in a game or an animation, because inside the form there is a topology with a random number of corners and triangular “fans” where a smooth bend should be.
The “Clean Mesh” trainer is exactly about this: three meshes that look the same, one bend, and only one deforms predictably. Start with it: open the trainer.
#Session 8 — why quads matter
Imagine your character has to raise an arm, or your car has to open a door. Are you sure the mesh at the bend will cope? Most people haven’t thought about it, and that’s fine: today is exactly about this.
Quad, triangle or n-gon. The same form can be made of different faces:
| Face type | What it gives | The problem if it’s not where it should be |
|---|---|---|
| Quad (4 corners) | supports Loop Cut, easier UVs, predictable deformation | — (this is the goal) |
| Triangle | sometimes unavoidable (a cone’s tip, an edge) | a pile of triangles in a row = a pole: a point where too many edges meet; deforms badly |
| N-gon (5+ corners) | quickly closes a big flat area | doesn’t support Subdivision and Loop Cut predictably, especially in a bend zone |
Edge flow. Edge loops should run around a joint, like rings around a finger, not through it.
The MatCap check. In Viewport Shading → Solid pick a reflective MatCap instead of the flat material. On a bad, uneven mesh reflections “swim” and distort unevenly, on a clean one they lie smoothly. It’s a quick visual test you can do at any stage of the work.
Practice: diagnose your own object. Turn on MatCap on your object from block 3 and find problem zones: poles, n-gons, abrupt changes in mesh density. For now only find and mark them; fixing everything in one session isn’t required. Having several problem zones is normal: today’s goal is learning to see.
#Session 9 — retopology and the polygon budget
Why can’t you simply press Subdivide on a bad mesh and get a clean model? Because Subdivision amplifies the existing topology rather than fixing it: a bad mesh becomes a “smooth bad mesh”.
Retopology is building a new clean mesh over the old form, using circles and rectangles as basic “islands” of topology joined by predictable loops. Helpers:
- Shrinkwrap pulls the new clean mesh onto the surface of the old form;
- Decimate quickly simplifies a mesh that is too heavy — a rough start, not a substitute for manual retopology.
The polygon budget and LOD thinking. Are all parts of a model equally important for the polygon count? A character’s face, or a detail the camera sees up close, deserves more polygons than a sole or an inner, invisible part. Different levels of detail for different parts or distances is LOD thinking.
Practice. Rebuild the problem zones of your object — by hand or with Shrinkwrap/Decimate where it makes sense. You don’t have to rebuild the whole model: fixing the zones where movement will really happen (joints, hinges) is enough; the rest may stay as it is.
#Common problems
| Problem | Why it happened | The fix |
|---|---|---|
| MatCap shows no difference: the mesh looks equally “smooth” | The viewport is still in ordinary Solid mode with the standard material instead of a reflective MatCap | Viewport Shading → Solid → in the settings pick a reflective (metal or clay) MatCap instead of the flat one |
| Decimate makes the model equally rough everywhere | One overall simplification percentage was applied to the whole object regardless of important areas | Use Decimate with a Vertex Group (protect the important zones with weight) or simplify in parts by hand |
| After retopology with Shrinkwrap the new mesh “pokes through” or doesn’t sit on the old surface | Shrinkwrap targets the wrong shape, or the modifier order is mixed up | Check that Shrinkwrap targets the original (old) object and sits above Mirror/Subdivision in the stack |
#Before the session
- Blender 5.2 LTS; your object from block 3.
- Open “Clean Mesh” and play a few rounds: the best warm-up.
