matcap_shade — 3D `render` op

• Data kinds: normalmap × image2d → image2d

• Call: import fullseye as fs; fs.ledger.matcap_shade(normals, matcap) -> 'np.ndarray' (to call the implementation directly, import render_shade; render_shade.matcap_shade(normals, matcap) -> 'np.ndarray'; from the registry, ops3d.get("matcap_shade"))

Usage

MatCap: map view-space normals onto a lit-sphere texture to transfer a material's look. → (H, W[, C]).

Maps the view-space unit normal (nx, ny) ([-1,1]) to texture coordinates (u = (nx+1)/2, v = (1−ny)/2, flipping y along the row direction) and samples the matcap image with bilinear interpolation. Without any lighting computation, the material look of 1 shot of a lit sphere can be pasted directly onto any shape (metal, clay, toon, etc.).

matcap is a near-square lit-sphere texture:

• greyscale (h, w) → output (H, W)

• colour (h, w, C) (any C) → output (H, W, C)

The background (normals of length 0) is 0. Texture coordinates are clamped at the edges (normals at the sphere rim |(nx,ny)|→1 point to the texture edge).

fail-closed: invalid shapes, non-finite values and textures that are too small (h,w < 2) raise ValueError.

Background guides (the physics and conventions behind this op)

• blender_interop — Using Blender alongside — build the shape, measure it with fullseye (pitfalls: axes, units, ground truth)

References (sample data, literature)

• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).

• Operator provenance and references — the sources of the research/methods this op family came from.

Runnable examples (verified samples that actually call this op)

• render_shade — py -3.11 examples_3d/render_shade.py

Ops the type connects to (they accept `image2d` as input)

fuse_to_voxel · fit_poly_surface · eval_poly_surface · surface_form_error · background_flatten · polar_unwrap · fit_zernike · antialias

Same category (`render`)

project_points · render_point_depth · render_volume_projection · render_shaded · ambient_occlusion · cast_shadow · phong_shade · supersample_mesh

*Provenance: render_shade.py — 3D operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*

matcap_shade — 3D render op