screw thread v1

params = [
	{ "id": "r1", "displayName": "R1", "type": "float", "rangeMin": 0, "rangeMax": 100, "default": 10.0 },
	{ "id": "r2", "displayName": "R2", "type": "float", "rangeMin": 0, "rangeMax": 100, "default": 10.0 },
	{ "id": "height", "displayName": "Height", "type": "float", "rangeMin": 1.0, "rangeMax": 100.0, "default": 20.0 }
	{ "id": "pitch", "displayName": "Pitch", "type": "float", "rangeMin": 1.0, "rangeMax": 100.0, "default": 5.0 }


]

function process(params) {
	var height = params["height"];
	var r1 = params["r1"];
	var r2 = params["r2"];
/* r1 is the base and r2 is the top of the screw thread. If r1<r2, then this is an internal thread */

/* height is the total length of the thread */
/* pitch is the distance the thread advances per turn */
/* for now, set the tooth size to 3/4 of the pitch, with the rise, top, fall and gap all 1.4 of the pitch */

	var rise=pitch/4;
	var fall=rise;
	var top=rise;
	var gap=rise;

/* ndivs is the number of steps around the circle */
	var ndivs = Tess.circleDivisions(Math.max(r1,r2));
	var n = ndivs*params.height/params.pitch;
/* n is the total number of steps */

/* set up the mesh  */

	var mesh = new Mesh3D();

/* set up the first face */

	var x0 = r1;
	var x1=r2;
	var y0=0;
	var y1=0;
	var z0=0;
	var z1=rise;
	var z2 = z1+top;
	var z3 = z2+fall;

/* calculate the amount the screw rises over each step */
	var  lift = pitch/ndivs;

	mesh.quad([x0, y0, z0, x1,y1,z1,x1,y1,z2,x0,y0,z3]);

	for (var i = 0; i < n; i++) {
		var theta = (i+1)/ndivs * Math.PI*2;
		var s = Math.sin(theta);
		var c = Math.cos(theta);

		var x2 = r1*c;
		var x3 = r2*c;
		var y2 = r1*s;
		var y3 = r2*s;
		var z4 = (i+1)*lift;
		var z5 = z4 + rise;
		var z6 = z5 + top;
		var z7 = z6+fall;

/* add 4 quads: base, underside, end and top side */

		mesh.quad([x0, y0,z0,x2,y2,z4,x2,y2,z7,x0,y0,z3]);
		mesh.quad([x0,y0,z0,x1,y1,z1,x3,y3,z5,x2,y2,z4]);
		mesh.quad([x1,y1,z1,x1,y1,z2,x3,y3,z6,x3,y3,z5]);
		mesh.quad([x0,y0,z3,x1,y1,z2,x3,y3,z6,x2,y2,z7]);

/* shift vertices */
		x0=x2;
		x1=x3;
		y0=y2;
		y1= y3;
		z0=z4;
		z1=z5;
		z2=z6;
		z3=z7;

	}

/* add end cap */

	mesh.quad([x0, y0, z0, x1,y1,z1,x1,y1,z2,x0,y0,z3]);

	var solid = Solid.make(mesh);
	return solid;
}