BCad fork

Extended ≺code≻polygon()≺/code≻ syntax
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Extended ≺code≻polygon()≺/code≻ syntax

BCad extends the standard OpenSCAD polygon() with per-corner fillets/chamfers and spline sub-lists. The original syntax is fully preserved — every valid OpenSCAD polygon() call works identically in BCad.

Original syntax (OpenSCAD-compatible)

polygon([ [x,y], ... ], paths=[ ... ], convexity=1);

Each point is [x, y]. Optional paths controls vertex traversal order.

Extended point formats

Corner modifiers: [x, y, r]

A third element in a point triple adds a fillet or chamfer at that corner.

Value of r Effect
r > 0 Fillet with radius r (circular arc)
r < 0 Chamfer with distance -r (straight cut)
r = 0 No modifier (same as [x, y]) 
// Square with a 2-unit fillet at bottom-left corner
polygon([[0, 0, 2], [10, 0], [10, 10], [0, 10]]);

// Square with a 2-unit chamfer at bottom-left corner
polygon([[0, 0, -2], [10, 0], [10, 10], [0, 10]]);

// All four corners filleted
polygon([[0, 0, 2], [10, 0, 2], [10, 10, 2], [0, 10, 2]]);

// All four corners chamfered
polygon([[0, 0, -2], [10, 0, -2], [10, 10, -2], [0, 10, -2]]);

// Mixed fillets and chamfers
polygon([[0, 0, 2], [0, 10, -2], [10, 10, 2], [10, 0]]);

Fillet/chamfer modifiers work with explicit paths as well — the modifier follows the point it is attached to, regardless of traversal order.

Spline sub-lists: [[x1,y1], [x2,y2], ...]

A sub-list of 2D points replaces the straight edge with a B-spline that passes through the listed intermediate points. The spline starts at the previous vertex and ends at the next vertex in the path (the sub-list itself defines only the interior control points).

// Straight edges except one curved edge (spline through [5,5])
polygon([[0, 0], [[5, 5], [10, 0]], [10, 10], [0, 10]]);

Spline with corner modifier: [[x1,y1], ..., r]

A trailing number after the spline points applies a fillet or chamfer at the corner where the spline ends — the same convention as [x, y, r].

// Spline edge with a fillet of radius 2 at the end corner
polygon([[0, 0], [[5, 8], [10, 0], 2], [10, 10], [0, 10]]);

// Spline edge with a chamfer of distance 3 at the end corner
polygon([[0, 0], [[5, 8], [10, 0], -3], [10, 10], [0, 10]]);

Combining modifiers

All formats can be mixed freely in a single polygon:

polygon([
    [0, 0, 2],              // fillet r=2
    [10, 0, -2],            // chamfer d=2
    [10, 10, 2],            // fillet r=2
    [10, 0]                  // no modifier
]);

OpenSCAD compatibility

Feature OpenSCAD BCad
polygon([[x,y], ...]) supported supported (identical)
paths parameter supported supported (identical)
convexity parameter supported accepted, ignored
[x, y, r] corner modifiers not supported BCad extension
Spline sub-lists not supported BCad extension
Spline [[...], r] modifier not supported BCad extension

All OpenSCAD-compatible polygon() calls produce identical geometry in BCad. The extensions are purely additive — no existing syntax is reinterpreted.

Technical notes