Tube mesh extrusion library for OpenSCAD

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This is a library for generating "tube-like" meshes that join a number of cross-sections. For instance, one could use this for a wing profile, or a sphere, or thread. The cross-sections don't have to planar, nor do they have to have the same number of points, but self-intersection of the resulting tube is likely to be a problem. There is some optimization done to make triangles in the meshes be closer to equilateral. One of the cool things one can do with this is "morph" between two plane shapes. For instance, morphExtrude(ngonPoints(30,d=6), ngonPoints(2,d=4), height=10); produces a wedge whose bottom is a circle of radius 3, and whose top is a line of length 4, while morphExtrude([ [0,0], [20,0], [20,10], [0,10] ], [ [ 5,10 ] ], height=20 ); makes a pyramid with a rectangular base. The main low-level API is the module tubeMesh(sections,startCap=true,endCap=true,optimize=1) which takes a vector of three-dimensional counterclockwise cross-sections, and generates a polyhedron. The `optimize` parameter controls triangle optimization. For smooth twisty things, you might want to increase it to 4 or 5, but for less smooth things, it might screw things up. If you are having problems, set it to 0 or 1. There is also the higher-level module morphExtrude(section1,section2=undef,height=undef,numSlices=10,startCap=true,endCap=true,optimize=1,twist=0,curve="t") This has two modes of operation. If `height` is undefined, you feed it two three-dimensional sections (if you omit section2, it is the same as section1), and it interpolates between them to generate `numSlices` layers. If `height` is defined, you feed it two two-dimensional sections, and interpolation between the two sections separated by the specified `height` is generated. The `twist` is mainly for fun. If you specify the `curve` parameter, and `height` is defined, then the interpolation parameter, which normally linearly changes from 0 to 1 with the z coordinate, is transformed according to the function specified by `curve`. For instance, the pointy pyramid in the demo is done with: morphExtrude([ [0,0], [20,0], [20,10], [0,10] ], [ [ 10,5 ] ], height=20, curve="sin(90*t)" ); You can use most of the standard OpenSCAD functions and operations for specifying the curve. See [here](https://www.thingiverse.com/thing:2295309) for details. If you want to reference some parameters in your formula, you can add a `curveParams=[["paramA",valueA],["paramB",valueB],...]` argument to `morphExtrude()`. If you want access to the points and faces behind `tubeMesh()`, call `pointsAndFaces()` with the same arguments. This returns a `[points,faces]` vector. In fact, `tubeMesh()` is equivalent to calling `polyhedron()` with the output of `pointsAndFaces()`. As a demo, there is a `cone()` module and a `mySphere()` module. The latter has the same parameters as the built-in `sphere()` primitive, but it uses a golden-angle spiral to generate a sphere whose triangles are more uniformly sized than those from the built-in module. There are also some useful utility functions: * `ngonPoints(n=4,r=10,d=undef,rotate=0,z=undef)`: generate the points of a regular `n`-gon; 2D unless `z` is specified * `starPoints(n=10,r1=5,r2=10,rotate=0,z=undef)`: generate the points of a star; 2D unless `z` is specified * `roundedSquarePoints(size=[10,10],radius=2,z=undef)`: generate the points of a rounded square; 2D unless `z` is specified * `sectionZ(section,z)`: takes a list of 2D points and add a z-coordinate to them all * `shiftSection(section,delta)`: adds `delta` to every point in the `section` list. **Updates:** **March 13, 2019:** Better mesh optimization for smooth twisting things; `twist` parameter reversed in direction to match `linear_extrude()` **March 11, 2019:** Can omit section2 parameter to `morphExtrude()`. **January 14, 2019:** Works without the `eval.scad` library if you don't use the curve parameter. There will be some warnings, but they can be ignored. **November 18, 2018:** Added `curve` parameter to `morphExtrude()`. **November 21, 2017:** Added `roundedSquarePoints()`, `sectionZ()` and `shiftSection()`. **September 17, 2017:** Added `tubeMesh()` module for convenience.