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adding convexivity test and fan method for convex polygon triangulation
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@rahwang
rahwang committed Jun 15, 2017
1 parent 50d26f4 commit 7e82e90
Showing 1 changed file with 53 additions and 20 deletions.
73 changes: 53 additions & 20 deletions lib/loadObj.js
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Original file line number Diff line number Diff line change
Expand Up @@ -49,13 +49,13 @@ function Primitive() {
}

// OBJ regex patterns are modified from ThreeJS (https://github.com/mrdoob/three.js/blob/master/examples/js/loaders/OBJLoader.js)
var vertexPattern = /v( +[\d|\.|\+|\-|e|E]+)( +[\d|\.|\+|\-|e|E]+)( +[\d|\.|\+|\-|e|E]+)/; // v float float float
var normalPattern = /vn( +[\d|\.|\+|\-|e|E]+)( +[\d|\.|\+|\-|e|E]+)( +[\d|\.|\+|\-|e|E]+)/; // vn float float float
var uvPattern = /vt( +[\d|\.|\+|\-|e|E]+)( +[\d|\.|\+|\-|e|E]+)/; // vt float float
var facePattern1 = /f(\s+-?\d+\/?\/?){3,}/; // f vertex vertex vertex ...
var facePattern2 = /f(\s+-?\d+\/-?\d+){3,}/; // f vertex/uv vertex/uv vertex/uv ...
var facePattern3 = /f(\s+-?\d+\/-?\d+\/-?\d+){3,}/; // f vertex/uv/normal vertex/uv/normal vertex/uv/normal ...
var facePattern4 = /f(\s+-?\d+\/\/-?\d+){3,}/; // f vertex//normal vertex//normal vertex//normal ...
var vertexPattern = /v( +[\d|\.|\+|\-|e|E]+)( +[\d|\.|\+|\-|e|E]+)( +[\d|\.|\+|\-|e|E]+)/; // v float float float
var normalPattern = /vn( +[\d|\.|\+|\-|e|E]+)( +[\d|\.|\+|\-|e|E]+)( +[\d|\.|\+|\-|e|E]+)/; // vn float float float
var uvPattern = /vt( +[\d|\.|\+|\-|e|E]+)( +[\d|\.|\+|\-|e|E]+)/; // vt float float
var facePattern1 = /f(\s+-?\d+\/?\/?){3,}/; // f vertex vertex vertex ...
var facePattern2 = /f(\s+-?\d+\/-?\d+){3,}/; // f vertex/uv vertex/uv vertex/uv ...
var facePattern3 = /f(\s+-?\d+\/-?\d+\/-?\d+){3,}/; // f vertex/uv/normal vertex/uv/normal vertex/uv/normal ...
var facePattern4 = /f(\s+-?\d+\/\/-?\d+){3,}/; // f vertex//normal vertex//normal vertex//normal ...

var faceSpacePattern = /f?\s+/;
var faceSpaceOrSlashPattern = /(f?\s+)|(\/+\s*)/g;
Expand Down Expand Up @@ -279,6 +279,29 @@ function loadObj(objPath, options) {
return index;
}

// Given a sequence of three points A B C, determine whether vector BC
// "turns" clockwise (positive) or counter-clockwise (negative) from vector AB
var scratch1 = new Cartesian3();
var scratch2 = new Cartesian3();
function getTurnDirection(pointA, pointB, pointC) {
var vector1 = Cartesian2.subtract(pointA, pointB, scratch1);
var vector2 = Cartesian2.subtract(pointC, pointB, scratch2);
return vector1.x * vector2.y - vector1.y * vector2.x;
}

// Given the cartesian 2 vertices of a polygon, determine if convex
function isConvex(positions2D) {
var i;
var turnDirection = getTurnDirection(positions2D[0], positions2D[1], positions2D[2]);
for (i=1; i < positions2D.length-2; ++i) {
var currentTurnDirection = getTurnDirection(positions2D[i], positions2D[i+1], positions2D[i+2]);
if (turnDirection * currentTurnDirection < 0) {
return false;
}
}
return true;
}

function addFace(vertices, positions, uvs, normals) {

var u1, u2, u3, n1, n2, n3;
Expand Down Expand Up @@ -309,34 +332,44 @@ function loadObj(objPath, options) {
var vertexIndices = [];

var i;
for (i=0; i < vertices.length; ++i) {
for (i = 0; i < vertices.length; ++i) {
var u = (defined(uvs)) ? uvs[i] : undefined;
var n = (defined(normals)) ? normals[i] : undefined;

var index = addVertex(vertices[i], positions[i], u, n);
vertexIndices.push(index);

var pi = getOffset(index+1, positions, 3);
// Collect the vertex positions as 3D points
var pi = getOffset(index + 1, positions, 3);
var px = mesh.positions.get(pi + 0);
var py = mesh.positions.get(pi + 1);
var pz = mesh.positions.get(pi + 2);

positions3D.push(new Cartesian3(px, py, pz));
}
var positions2D = projectTo2D(positions3D);

var windingOrder = PolygonPipeline.computeWindingOrder2D(positions2D);
var positions2D = projectTo2D(positions3D);

// Since the projection doesn't respect winding order, reverse the order of
// the vertices before triangulating to enforce counter clockwise.
if (windingOrder === WindingOrder.CLOCKWISE) {
positions2D.reverse();
}
if (isConvex(positions2D)) {
// Use the fan method to triangulate
for (i=1; i < vertices.length-1; ++i) {
primitive.indices.push(vertexIndices[0]);
primitive.indices.push(vertexIndices[i]);
primitive.indices.push(vertexIndices[i+1]);
}
} else {

var positionIndices = PolygonPipeline.triangulate(positions2D);
// Since the projection doesn't respect winding order, reverse the order of
// the vertices before triangulating to enforce counter clockwise.
var windingOrder = PolygonPipeline.computeWindingOrder2D(positions2D);
if (windingOrder === WindingOrder.CLOCKWISE) {
positions2D.reverse();
}

for (i=0; i < positionIndices.length; ++i) {
primitive.indices.push(vertexIndices[positionIndices[i]]);
// Use an ear-clipping algorithm to triangulate
var positionIndices = PolygonPipeline.triangulate(positions2D);
for (i = 0; i < positionIndices.length; ++i) {
primitive.indices.push(vertexIndices[positionIndices[i]]);
}
}
}

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