xiaoyan159/vtm
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

add ear-clip triangulator, might be more efficient for simple polys

Browse Source
This commit is contained in:
Hannes Janetzek 2013-02-10 12:20:04 +01:00
parent 344f4d7030
commit c64e0fe5b0
1 changed files with 365 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

365
src/org/oscim/utils/Triangulator.java Normal file
View File

@ -0,0 +1,365 @@
package org.oscim.utils;
import java.util.ArrayList;
/**
* Triangulates a polygon into triangles - duh. Doesn't handle
* holes in polys
*
* @author Public Source from FlipCode
*/
public class Triangulator {
/** The accepted error value */
private static final float EPSILON = 0.0000000001f;
/** The list of points to be triangulated */
private PointList poly = new PointList();
/** The list of points describing the triangles */
private PointList tris = new PointList();
/** True if we've tried to triangulate */
private boolean tried;
/**
* Create a new triangulator
*/
public Triangulator() {
}
/**
* Add a point describing the polygon to be triangulated
*
* @param x The x coordinate of the point
* @param y the y coordinate of the point
*/
public void addPolyPoint(float x, float y) {
poly.add(new Point(x, y));
}
/**
* Cause the triangulator to split the polygon
*
* @return True if we managed the task
*/
public boolean triangulate() {
tried = true;
boolean worked = process(poly, tris);
return worked;
}
/**
* Get a count of the number of triangles produced
*
* @return The number of triangles produced
*/
public int getTriangleCount() {
if (!tried) {
throw new RuntimeException("Call triangulate() before accessing triangles");
}
return tris.size() / 3;
}
/**
* Get a point on a specified generated triangle
*
* @param tri The index of the triangle to interegate
* @param i The index of the point within the triangle to retrieve
* (0 - 2)
* @return The x,y coordinate pair for the point
*/
public float[] getTrianglePoint(int tri, int i) {
if (!tried) {
throw new RuntimeException("Call triangulate() before accessing triangles");
}
return tris.get((tri * 3) + i).toArray();
}
/**
* Find the area of a polygon defined by the series of points
* in the list
*
* @param contour The list of points defined the contour of the polygon
* (Vector2f)
* @return The area of the polygon defined
*/
private static float area(PointList contour) {
int n = contour.size();
float A = 0.0f;
for (int p = n - 1, q = 0; q < n; p = q++) {
Point contourP = contour.get(p);
Point contourQ = contour.get(q);
A += contourP.getX() * contourQ.getY() - contourQ.getX()
* contourP.getY();
}
return A * 0.5f;
}
/**
* Check if the point P is inside the triangle defined by
* the points A,B,C
*
* @param Ax Point A x-coordinate
* @param Ay Point A y-coordinate
* @param Bx Point B x-coordinate
* @param By Point B y-coordinate
* @param Cx Point C x-coordinate
* @param Cy Point C y-coordinate
* @param Px Point P x-coordinate
* @param Py Point P y-coordinate
* @return True if the point specified is within the triangle
*/
private static boolean insideTriangle(float Ax, float Ay, float Bx,
float By, float Cx, float Cy, float Px, float Py) {
float ax, ay, bx, by, cx, cy, apx, apy, bpx, bpy, cpx, cpy;
float cCROSSap, bCROSScp, aCROSSbp;
ax = Cx - Bx;
ay = Cy - By;
bx = Ax - Cx;
by = Ay - Cy;
cx = Bx - Ax;
cy = By - Ay;
apx = Px - Ax;
apy = Py - Ay;
bpx = Px - Bx;
bpy = Py - By;
cpx = Px - Cx;
cpy = Py - Cy;
aCROSSbp = ax * bpy - ay * bpx;
cCROSSap = cx * apy - cy * apx;
bCROSScp = bx * cpy - by * cpx;
return ((aCROSSbp >= 0.0f) && (bCROSScp >= 0.0f) && (cCROSSap >= 0.0f));
}
/**
* Cut a the contour and add a triangle into V to describe the
* location of the cut
*
* @param contour The list of points defining the polygon
* @param u The index of the first point
* @param v The index of the second point
* @param w The index of the third point
* @param n ?
* @param V The array to populate with indicies of triangles
* @return True if a triangle was found
*/
private static boolean snip(PointList contour, int u, int v, int w, int n,
int[] V) {
int p;
float Ax, Ay, Bx, By, Cx, Cy, Px, Py;
Ax = contour.get(V[u]).getX();
Ay = contour.get(V[u]).getY();
Bx = contour.get(V[v]).getX();
By = contour.get(V[v]).getY();
Cx = contour.get(V[w]).getX();
Cy = contour.get(V[w]).getY();
if (EPSILON > (((Bx - Ax) * (Cy - Ay)) - ((By - Ay) * (Cx - Ax)))) {
return false;
}
for (p = 0; p < n; p++) {
if ((p == u) || (p == v) || (p == w)) {
continue;
}
Px = contour.get(V[p]).getX();
Py = contour.get(V[p]).getY();
if (insideTriangle(Ax, Ay, Bx, By, Cx, Cy, Px, Py)) {
return false;
}
}
return true;
}
/**
* Process a list of points defining a polygon
*
* @param contour The list of points describing the polygon
* @param result The list of points describing the triangles. Groups
* of 3 describe each triangle
* @return True if we succeeded in completing triangulation
*/
private static boolean process(PointList contour, PointList result) {
/* allocate and initialize list of Vertices in polygon */
int n = contour.size();
if (n < 3)
return false;
int[] V = new int[n];
/* we want a counter-clockwise polygon in V */
if (0.0f < area(contour)) {
for (int v = 0; v < n; v++)
V[v] = v;
} else {
for (int v = 0; v < n; v++)
V[v] = (n - 1) - v;
}
int nv = n;
/* remove nv-2 Vertices, creating 1 triangle every time */
int count = 2 * nv; /* error detection */
for (int m = 0, v = nv - 1; nv > 2;) {
/* if we loop, it is probably a non-simple polygon */
if (0 >= (count--)) {
//** Triangulate: ERROR - probable bad polygon!
return false;
}
/* three consecutive vertices in current polygon, <u,v,w> */
int u = v;
if (nv <= u)
u = 0; /* previous */
v = u + 1;
if (nv <= v)
v = 0; /* new v */
int w = v + 1;
if (nv <= w)
w = 0; /* next */
if (snip(contour, u, v, w, nv, V)) {
int a, b, c, s, t;
/* true names of the vertices */
a = V[u];
b = V[v];
c = V[w];
/* output Triangle */
result.add(contour.get(a));
result.add(contour.get(b));
result.add(contour.get(c));
m++;
/* remove v from remaining polygon */
for (s = v, t = v + 1; t < nv; s++, t++) {
V[s] = V[t];
}
nv--;
/* resest error detection counter */
count = 2 * nv;
}
}
return true;
}
/**
* A single point handled by the triangulator
*
* @author Kevin Glass
*/
private class Point {
/** The x coorindate of this point */
private float x;
/** The y coorindate of this point */
private float y;
/**
* Create a new point
*
* @param x The x coordindate of the point
* @param y The y coordindate of the point
*/
public Point(float x, float y) {
this.x = x;
this.y = y;
}
/**
* Get the x coordinate of the point
*
* @return The x coordinate of the point
*/
public float getX() {
return x;
}
/**
* Get the y coordinate of the point
*
* @return The y coordinate of the point
*/
public float getY() {
return y;
}
/**
* Convert this point into a float array
*
* @return The contents of this point as a float array
*/
public float[] toArray() {
return new float[] { x, y };
}
}
/**
* A list of type <code>Point</code>
*
* @author Kevin Glass
*/
private class PointList {
/** The list of points */
private ArrayList<Point> points = new ArrayList<Point>();
/**
* Create a new empty list
*/
public PointList() {
}
/**
* Add a point to the list
*
* @param point The point to add
*/
public void add(Point point) {
points.add(point);
}
/**
* Remove a point from the list
*
* @param point The point to remove
*/
public void remove(Point point) {
points.remove(point);
}
/**
* Get the size of the list
*
* @return The size of the list
*/
public int size() {
return points.size();
}
/**
* Get a point a specific index in the list
*
* @param i The index of the point to retrieve
* @return The point
*/
public Point get(int i) {
return points.get(i);
}
}
}