Rebuild clean topology with Retopo

What you'll learn#

You will take the dense mesh from Sculpt and rebuild a clean, low-density topology on top of it in Retopo. This is the step that makes a sculpt usable in a game engine, and it is also what makes texturing behave.

Before you start#

• Finish Sculpt your first prop, or have any high-density mesh ready.
• Retopo is a backed module, like Sculpt.
• It runs on WebGL, and only WebGL. Any browser with a working 3D context opens it.
• Useful to know: a sculpt is millions of triangles with no usable layout. A retopologised mesh is a few thousand quads arranged to follow the form.

Steps#

1. Send the mesh across from Sculpt with Send to Retopo. The high-poly arrives as the reference surface you will draw on. You can also import a file directly: Retopo reads .obj, .stl and .json.

2. Open Retopo and confirm the reference mesh is visible in the viewport. Everything you build from here snaps onto that surface.

3. Enable symmetry if your prop is symmetrical. Building one half and letting the other mirror saves most of the work. Skip this for an irregular shape such as a rock.

4. Run Auto Retopo with a target polygon count. Start low, in the low thousands, and look at the result before raising it. A rock does not need more.

   Tip: the right target is the lowest count that still holds the silhouette. Zoom out until the prop is the size it will be on screen in the final scene, and judge from there.

5. Inspect the generated topology. You are checking two things: that the silhouette survived, and that the density is roughly even rather than bunched in one corner.

6. Fix problem areas by hand. Draw quads directly on the reference surface where Auto Retopo missed a crease or wasted geometry on a flat face.

   Tip: follow the form. Loops that run along a crease or around a mass deform predictably and shade cleanly. Loops that cut across them do neither.

7. Adjust density where it matters. Put more geometry where the shape changes fast and less on the large flat areas.

8. Check the UVs before you leave the module. Texturing in Pigment reads this layout, and a broken layout shows up as stretched or smeared texture later.

   Warning: it is much cheaper to fix UVs here than to discover the problem after you have painted a full material set.

9. Save the result, then send it onward with Send to Pigment.

Result#

You now have two meshes of the same prop: the dense sculpt, and a light quad mesh that matches its shape. The light one is what ships. The dense one still matters, because Pigment bakes surface detail from it in the next tutorial.

Going further#

• Next in the pipeline: texture the prop in Pigment.
• Keep both meshes. Baking needs the high-poly, and you cannot recover it once it is gone.
• Try the same prop at two different polygon targets and compare how each holds up at distance.