Rendered from src/SLICING.md in the repository — edit it there.

Slicing Algorithm

Converts 3D triangle meshes into layer-by-layer 2D contours by intersecting triangles with horizontal planes.

How It Works

Step by Step

1. Layer Range

Model Z extent: 0 to 50 mm
Layer height: 0.2 mm
→ 250 layers at Z = 0, 0.2, 0.4, ..., 49.8, 50.0

2. Triangle-Plane Intersection

For each triangle, check if it crosses the plane at height Z:

Triangle vertices: A(z=1), B(z=3), C(z=2)
Plane at Z=2.5

A(z=1) is below ✓
B(z=3) is above ✓
→ Triangle crosses! Intersect edges AB and BC

3. Interpolate XY Points

Where edge crosses the plane:

Edge from A(x=0, y=0, z=1) to B(x=10, y=10, z=3)
Plane at Z=2.5

t = (2.5 - 1) / (3 - 1) = 0.75
x = 0 + 0.75 * 10 = 7.5
y = 0 + 0.75 * 10 = 7.5
→ Intersection at (7.5, 7.5)

4. Chain into Closed Paths

Connect intersection points into loops (contours):

Example: Pyramid Slicing

Input: Pyramid with 10×10 mm base at Z=0, apex at Z=10 mm
Layer height: 2 mm

Result:
Z=0:  10×10 mm square (base)
Z=2:   8×8 mm square (tapered)
Z=4:   6×6 mm square
Z=6:   4×4 mm square
Z=8:   2×2 mm square
Z=10: point (apex)

Each layer is a horizontal "slice" through the model.

Integration

Usage:

let mesh = load_stl("model.stl")?;
let layers = slice_mesh(&mesh, 0.2);  // 0.2 mm layer height
let gcode = generate_gcode(&layers, &params);

Key Concepts

Concept	Meaning
SliceLayer	One horizontal slice at height Z with closed contour paths
Paths	Set of closed loops (from Clipper2) representing contours
Z-ordering	Layers stack bottom-to-top for printing
Degenerate triangles	Area ≈ 0; skipped during intersection

Performance

• Time: O(triangles × layers)
• Space: O(layers + total segments)

Optimization: Cache triangle Z-extents to skip impossible layers.

Limitations

• No infill generation (future)
• No support structure (future)
• Assumes manifold mesh (closed, no holes)

See Also

• Mesh Loading – How STL is parsed
• Settings – Layer height configuration
• G-code – Converting layers to printer commands
• Root – Overview