contour-to-mesh

MCP backend

Use when: Source-locked contour-derived meshes, silhouette-first modeling, triangulated mask/contour surfaces, mesh generation from OpenCV contours, or replacing generic ellipses/primitives with measured shapes.

Before the first Blender call, read ../text-to-blender/references/mcp-backends.md. Prefer official MCP for shared capabilities; preserve the selected backend for the whole task. Tool names in recipes are client/legacy examples: map them through that reference and its agent-host guide.

Contour to Mesh

Use this when a reference silhouette is the contract. The mesh starts as a filled 2D contour in front-view X/Z, then gets shallow Y depth/crown after validation.

Workflow

1. Extract or select a clean contour/mask for one structural part.
2. Generate a triangulated mesh recipe with scripts/mask_to_mesh_recipe.py.
3. Run the generated Blender Python to create a named GEO_* mesh.
4. Assign front-projected UVs immediately.
5. Add depth only as a modifier or vertex displacement that preserves X/Z boundary positions.
6. Validate the front render against the source mask.

Hard rules

• Do not use radial duplication unless the manifest says the source is symmetric.
• Do not use a generic ellipse if a contour exists.
• Boundary vertices must keep source X/Z coordinates.
• Depth deformation may move Y and inner vertices, but must not alter front silhouette.
• One structural source part should become one named structural mesh.

Blender pattern

Generated mesh coordinates should map image x to Blender X and image y to Blender Z with vertical flip. Use Y only for thickness/depth.

Front-plane rotation rule

In this Blender coordinate convention, the front camera looks along the Y axis and the reference silhouette lives in the X/Z plane. Therefore 2D rotations inside the front view are rotations around the Y axis, not around Z. Use rotation_euler = (0, angle, 0) for 2D component orientation in the front projection. Z rotation spins objects into/out of screen-space incorrectly for X/Z-plane meshes.

Sources distilled

• Blender Mesh API: create meshes from vertices/faces using from_pydata.
• Blender BMesh: use for cleanup, triangulation, normals, smoothing.
• OpenCV contours: detect and simplify boundaries.
• Delaunay triangulation: useful for filled interior meshes when filtered by mask containment.

Part-inventory handoff

When masks come from source-part-segmentation, preserve the part_inventory.json names in Blender: GEO_<part_name>, MAT_<part_name>, and UV layer names. Mesh generation must record:

• source image size;
• source mask path;
• contour boundary point count;
• boundary landmark points (tip, base-left, base-right, centroid/extrema) when detectable;
• atlas UV rectangle or projection mode.

For exact mascot/logo work, generate boundary vertices from the contour and add interior vertices only for surface support. The boundary is a contract: bevels, solidify, subdivision, shrinkwrap, or sculpt passes must not move front-view X/Z boundary vertices unless a new source mask is produced.

Hole and stroke policy

• Filled structural masks become meshes.
• Wireframe strokes guide boundaries/landmarks; they are not structural meshes unless the manifest classifies them as decorative linework.
• Holes/negative regions should be kept as separate cut masks when they affect silhouette; otherwise implement them as decals/material masks.

Source-locked front-skin fallback

When a design sheet is painterly/stylized and separate orthographic views are not CAD-consistent, use a front-skin pass before sculptural interpretation:

1. choose the canonical front/master source;
2. extract the visible subject mask as a filled contour;
3. create a shallow 2.5D mesh whose X/Z boundary is that contour;
4. assign full-image front-projected UVs so the rendered front matches the source pixels;
5. add depth only along Y and behind the front surface;
6. optionally add separate relief/backing parts for side plausibility, but keep the front skin as the visual acceptance gate.

This is a generic fallback for logos/mascots where a faithful front read is more important than speculative volume. Mark it as front_locked_visual_skin, not as a fully solved turntable model.

Script

• scripts/source_locked_skin_recipe.py extracts a largest/canonical foreground component and emits a mask + contour mesh recipe using full-image front-projected UV coordinates.