primitive-capsule/index.js

A minimal capsule geometry for 3D rendering, including normals, UVs and cell indices (faces).

function createCapsule(radius, height, numSubdivisionsHeight, numSegments) {
  if (radius === undefined) radius = 0.5;
  if (height === undefined) height = radius * 2;
  if (numSubdivisionsHeight === undefined) numSubdivisionsHeight = 12;
  if (numSegments === undefined) numSegments = 12;

  var positions = [];
  var normals = [];
  var uvs = [];
  var cells = [];

  function calculateRing(segments, r, y, dy) {
    var segIncr = 1.0 / ( segments - 1 );

    for( var s = 0; s < segments; s++ ) {
      var x = -Math.cos( (Math.PI * 2) * s * segIncr ) * r;
      var z = Math.sin( (Math.PI * 2) * s * segIncr ) * r;

      positions.push([radius * x, radius * y + height * dy, radius * z])
      normals.push([x, y, z])

      var u = (s * segIncr);
      var v = 0.5 - ((radius * y + height * dy) / (2.0 * radius + height));
      uvs.push([u, 1.0 - v]);
    }
  }

  var ringsBody = numSubdivisionsHeight + 1;
  var ringsTotal = numSubdivisionsHeight + ringsBody;


  var bodyIncr = 1.0 / ( ringsBody - 1 );
  var ringIncr = 1.0 / ( numSubdivisionsHeight - 1 );
  for( var r = 0; r < numSubdivisionsHeight / 2; r++ ) {
    calculateRing( numSegments, Math.sin( Math.PI * r * ringIncr), Math.sin( Math.PI * ( r * ringIncr - 0.5 ) ), -0.5 );
  }

  for( var r = 0; r < ringsBody; r++ ) {
    calculateRing( numSegments, 1.0, 0.0, r * bodyIncr - 0.5);
  }

  for( var r = numSubdivisionsHeight / 2; r < numSubdivisionsHeight; r++ ) {
    calculateRing( numSegments, Math.sin( Math.PI * r * ringIncr), Math.sin( Math.PI * ( r * ringIncr - 0.5 ) ), +0.5);
  }

  for( var r = 0; r < ringsTotal - 1; r++ ) {
    for( var s = 0; s < numSegments - 1; s++ ) {
      cells.push([
        (r * numSegments + ( s + 0 )),
        (r * numSegments + ( s + 1 )),
        (( r + 1 ) * numSegments + ( s + 1 ))
      ]);
      cells.push([
        (r * numSegments + s),
        (( r + 1 ) * numSegments + ( s + 1 )),
        (( r + 1 ) * numSegments + ( s + 0 ))
      ])
    }
  }

  return {
    positions: positions,
    normals: normals,
    uvs: uvs,
    cells: cells
  }
}

module.exports = createCapsule;