Quad retopology and detail projection

QRemesh rebuilds a sculpt as clean, all-quad topology whose edge loops follow the forms, like ZBrush's ZRemesher. ProjectAll then moves a mesh onto the surface of other SubTools, so the detail of the original sculpt comes back onto the new topology, like ZBrush's Project All. Together they turn a dense, messy sculpt (a voxel remesh, a scan, an AI-generated model) into a light quad mesh you can divide, sculpt on, unwrap and animate.

The usual workflow#

1. Select the sculpt and open Tool > Geometry. Under QRemesh, turn on Keep Original.
2. Set Target Polygons (for example 5000) and click QRemesh. It runs in the background: a progress bar replaces the button, and Cancel stops it. The result replaces the SubTool, and the sculpt as it was is kept as a hidden SubTool called "name Original" right below it.
3. Divide the new mesh two or three times (Tool > Geometry > Subdivide, Ctrl+D).
4. Show the original again (the eye in Tool > SubTool) and click ProjectAll under Tool > SubTool > Project. The divided quads snap onto the sculpt and take its polypaint.
5. Hide or delete the original. You now have the same sculpt on clean quads.

Both steps are single undo steps (Ctrl+Z).

QRemesh#

Tool > Geometry > QRemesh works on the active SubTool.

What happens to your data:

• The result is all quads (stored as pairs of triangles, so PolyF draws quads and OBJ, FBX, PLY, USD and GoZ export them as quads), closed wherever the sculpt is closed. Open edges of the sculpt stay open, along the same outline.
• Sculpt layers are baked into the surface: the result has no layers.
• Mask and polypaint are interpolated from the closest point of the sculpt (polypaint is blurred to the new resolution until you project it back onto a divided copy).
• Polygroups are kept with Keep Groups; otherwise the result is one polygroup. The old UVs are dropped. A painted texture is kept with Keep Texture (on by default): the result gets Auto UVs and the texture, every layer of it, is projected onto them from the old surface, in the same undo step. See Texture painting.
• Hidden parts are remeshed too.
• Separate pieces stay separate and none is dropped: small ones (eyes, teeth, rivets, anything that would get fewer than about 100 quads) are remeshed on their own with at least 32 quads, more for small round pieces with Adaptive Size. A piece the grid can't cover at all is kept as it was (as triangles).
• Thin parts (a blade, a fin, a slab thinner than a quad) keep both their sides, and with Detect Edges their hard edges keep a loop each and their corners stay put. Their corners can still be cut a little when the part is much thinner than a quad: raise the target, or use polypaint density there.

Guiding the edge flow#

• QRemesh Guides put an edge loop exactly where you draw: around the eyes, the mouth, a joint. See below.
• Polygroups are as strong a guide. Paint a group around an eye, the mouth or a muscle, turn on Keep Groups, and loops will circle it. See Polygroups.
• Polypaint sets the density with Use Polypaint: paint the face red and the back of the head blue to spend the quads where they matter.
• Adaptive Size around 0.5 gives detailed areas more quads without your help; use 0 for an even mesh, for example before more sculpting.

How it works#

QRemesh is a field-aligned method after Instant Field-Aligned Meshes (Jakob, Tarini, Panozzo and Sorkine-Hornung, 2015). It smooths a cross field (the directions the quad edges should take) over the surface from coarse to fine, places a grid of the wanted size along it, extracts the polygons where neighbouring grid corners meet, splits every polygon into quads and relaxes them back onto the sculpt. It is fast: about 2 seconds for a 1.3-million-triangle sculpt to 5,000 quads, and 6 seconds to 100,000 quads, on a 10-core desktop.

QRemesh Guides#

Draw curves on the sculpt and QRemesh puts an edge loop along each one, and turns the flow around it to follow, like ZBrush's ZRemesher Guides brush. Use them where the topology has to work for animation: rings around the eyes and the mouth, loops around the shoulders, elbows and knees, a line down the middle of a muscle.

1. Click QRemesh Guides under Tool > Geometry > QRemesh (or pick it in the brush picker, B). The cursor becomes a small ring.
2. Drag on the model to draw a curve. It is drawn on the surface and snapped to it. A curve that ends near where it started is closed into a loop: draw round an eye and let go where you began.
3. With symmetry on (X in the top shelf), each curve is mirrored to the other side as you draw. A curve that is its own mirror image, a loop round the mouth across the middle, is kept once.
4. Click QRemesh. The status line says how many guides it followed.

Editing the curves:

• Alt+click a curve to delete it (it turns red under the cursor while Alt is held), with its mirror copy.
• Delete Last removes the last curve drawn; Clear removes them all.
• Ctrl still masks and Shift still smooths while the guides brush is picked, and dragging the background still turns the view. Pick any brush to sculpt again.

The guides belong to the SubTool: each SubTool has its own, they are saved in the project, and Keep Original gives the kept original a copy, so you can change them and remesh again. They show over the model, solid while the guides brush is picked and thin otherwise, so you can see the loop QRemesh put on them. Drawing and deleting guides isn't part of undo (Ctrl+Z undoes your sculpting as before).

Good to know:

• QRemesh snaps the guides onto the sculpt as it is when you run it, so sculpting after drawing them is fine. A guide left far from the surface, for example after moving the SubTool with the Gizmo, is ignored and the status line says so: draw it again.
• A loop gets an even number of quads around it, so it closes cleanly. Two guides closer together than about a quad compete for the same loop; draw them further apart or raise Target Polygons. A very small loop, about 25 quads round or fewer, may not close, and the edges just outside it bend to fit the extra quads the next ring needs: raise Target Polygons.
• Curves Strength doesn't change the loop on the curve, only how far around it the other edges turn to follow. Lower it when guides are close to each other or to the symmetry plane.

How the guides work#

Each curve constrains QRemesh's cross field (the directions the edges take) to run along it, falling off over a few quads (Curves Strength), and adds a lattice line on the curve, so one edge loop lies on it. Along a closed curve the lattice corners are placed at even steps, an even number of them (a ring of quads round a disk always has an even number of sides), so the loop meets itself without a kink. With symmetry QRemesh remeshes one half, so a loop across the middle is cut there: its corners start on the seam, where it meets its mirror image. QRemesh then checks the loops and the quads near the guides; if a loop came out broken or a fan of seven or more edges sits by a guide, it tries again with a different start for the field and keeps the best. Measured on a sphere with a circular guide around an "eye", the edges near the curve are within about 2 to 8 degrees of its direction (about 22 degrees without the guide), and the loop closes.

ProjectAll#

Tool > SubTool > Project > ProjectAll projects every other visible SubTool onto the active one. Each vertex looks along its normal, both ways, and moves to the nearest surface it finds within Dist; if there is none straight along the normal, it takes the closest point within Dist.

• The mask protects: fully masked vertices don't move; partly masked ones move part of the way. Mask the areas you have already fixed and project again with a different Dist.
• Hidden faces of the source are ignored, and hidden parts of the target don't move.
• ProjectAll is fast enough to use on dense meshes: about 0.6 seconds to project 1.25 million vertices from a 1.3-million-triangle sculpt.

Scripting#

sculptforge-cli -c 'open path=scan.glb; qremesh target=8000 adaptive=0.3 keep_original=true; subdivide levels=2; subtool_visibility index=1 visible=true; project_all distance=0.02; export_fbx path=retopo.fbx'

sculptforge-cli -c 'open path=head.glb; qremesh_guide points="0.2,0.3,2 0.3,0.4,2 0.4,0.3,2 0.3,0.2,2 0.2,0.3,2" view=0,0,-1 symmetry=x; qremesh target=4000 symmetry=x curves_strength=70'

From scripts qremesh runs straight away (it doesn't return until it's done); in the app the button runs it in the background.

See also#

• Subdivide, remesh, decimate and LODs: voxel remesh first to fuse pieces, subdivide after QRemesh
• SubTools: show, hide and duplicate the original
• Polygroups and visibility: guides for Keep Groups
• Projects: QRemesh Guides are saved with each SubTool
• Texture painting: Auto UV on the new topology