polyline-normals

Computes the normals of a polyline, using miter joins where multiple segments meet. This is mainly useful to expand thick lines in a vertex shader on the GPU.

var getNormals = require('polyline-normals')
 
//a triangle
var path = [ [0, 122], [0, 190], [90, 190] ]
 
//get the normals as a closed loop
var normals = getNormals(path, true)
 
//now draw our thick line in 2D/3D/etc

See the 2d test for an example of how these lines would be extruded.

For more complex line joins and end caps, see extrude-polyline (which builds an indexed mesh).

Shader Example

For an example of how to use this within a shader, see three-line-2d.

Usage

normals(path[, closed])

For the given path, produces a new array of the same length with normal information for each point. The data contains a normal, [nx, ny] and the length of the miter (default to 1.0 where no join occurs).

[ 
    [ [nx, ny], miterLength ],
    [ [nx, ny], miterLength ]
]

If closed is true, it assumes a segment will be drawn from the last point to the first point, and adjusts those normals accordingly.

License

MIT, see LICENSE.md for details.