Master of Puppets

Location

include/mop/interact/mesh_edit.h   — Public topology ops
src/interact/mesh_edit.c           — Half-edge structure + ops

Overview

Mesh editing operates on raw index-buffer topology. An auxiliary half-edge structure is built on demand from the index buffer; O(n²) twin-finding is acceptable for interactive edit operations. Every op finishes by recomputing normals and calling mop_mesh_update_geometry internally, so CPU and GPU buffers stay in sync and the next mop_viewport_render sees the new mesh.

These functions do not push undo themselves — wrap them in mop_viewport_push_undo on the calling side if you want undo.

Functions

Vertex ops

void mop_mesh_move_vertices  (MopMesh *m, MopViewport *vp,
                              const uint32_t *indices, uint32_t count,
                              MopVec3 delta);
void mop_mesh_delete_vertices(MopMesh *m, MopViewport *vp,
                              const uint32_t *indices, uint32_t count);
void mop_mesh_merge_vertices (MopMesh *m, MopViewport *vp,
                              uint32_t v0, uint32_t v1);

move: world-space delta added to each listed vertex; normals recomputed.
delete: removes listed vertices and any face that referenced them.
merge: welds v1 into v0; index buffer is remapped and degenerate faces are dropped.

Edge ops

void mop_mesh_split_edge   (MopMesh *m, MopViewport *vp,
                            uint32_t edge_v0, uint32_t edge_v1);
void mop_mesh_dissolve_edge(MopMesh *m, MopViewport *vp,
                            uint32_t edge_v0, uint32_t edge_v1);

split: inserts a midpoint vertex on the edge and rebuilds the adjacent triangles.
dissolve: removes the edge and merges the two adjacent faces into one.

Face ops

void mop_mesh_extrude_faces(MopMesh *m, MopViewport *vp,
                            const uint32_t *face_indices, uint32_t count,
                            float distance);
void mop_mesh_inset_faces  (MopMesh *m, MopViewport *vp,
                            const uint32_t *face_indices, uint32_t count,
                            float inset);
void mop_mesh_delete_faces (MopMesh *m, MopViewport *vp,
                            const uint32_t *face_indices, uint32_t count);
void mop_mesh_flip_normals (MopMesh *m, MopViewport *vp,
                            const uint32_t *face_indices, uint32_t count);

extrude: push faces along their averaged normals by distance; add side-wall quads around the extruded boundary.
inset: shrink each face toward its centroid by inset; fill the surrounding ring with quads.
delete: remove faces but keep vertices.
flip: reverse winding for the listed faces (and re-recompute normals).

Notes

Face index is the triangle number: face i occupies indices [i*3, i*3+3) in the index buffer.
Edge index is specified by its two endpoint vertices, not a separate edge ID.
Undo: the input path (MOP_INPUT_* events that drive the gizmo, etc.) pushes undo entries for the wrapping "drag operation", not per topology call. If you invoke these ops directly, push your own undo.
Selection does not auto-update: deleting faces / vertices may invalidate indices in the sub-element selection. Call mop_viewport_clear_selection (or re-select) after destructive ops.

Usage

Extrude the currently selected faces by 0.5 units along their normals:

const MopSelection *sel = mop_viewport_get_selection(vp);
if (sel->mode == MOP_EDIT_FACE && sel->element_count > 0) {
    mop_viewport_push_undo(vp, selected_mesh);
    mop_mesh_extrude_faces(selected_mesh, vp,
                           sel->elements, sel->element_count, 0.5f);
}

22 APR 2026

mesh edit