cocos2d-x 绘制多边形（凹形）问题

源码来自： http://www.flipcode.com/archives/Efficient_Polygon_Triangulation.shtml

CCDrawPloygon绘制多边形有凹形时，会多出一个三角形的区域。（如图下绘制五边形）

                                                                                            

方法一：

将五边形分成三个三角形，分别绘制。

方法二：

计算出可能存在凹形区域的三角位置（及三角形的顶点指标），然后通过CCClippingNode进行裁剪（ps：裁剪区域小可能有残余部分，所以我选的第一种）

计算方法：

// COTD Entry submitted by John W. Ratcliff [[e-mail]]// ** THIS IS A CODE SNIPPET WHICH WILL EFFICIEINTLY TRIANGULATE ANY// ** POLYGON/CONTOUR (without holes) AS A STATIC CLASS.  THIS SNIPPET// ** IS COMPRISED OF 3 FILES, TRIANGULATE.H, THE HEADER FILE FOR THE// ** TRIANGULATE BASE CLASS, TRIANGULATE.CPP, THE IMPLEMENTATION OF// ** THE TRIANGULATE BASE CLASS, AND TEST.CPP, A SMALL TEST PROGRAM// ** DEMONSTRATING THE USAGE OF THE TRIANGULATOR.  THE TRIANGULATE// ** BASE CLASS ALSO PROVIDES TWO USEFUL HELPER METHODS, ONE WHICH// ** COMPUTES THE AREA OF A POLYGON, AND ANOTHER WHICH DOES AN EFFICENT// ** POINT IN A TRIANGLE TEST.// ** SUBMITTED BY JOHN W. RATCLIFF ([e-mail]) July 22, 2000/**********************************************************************//************ HEADER FILE FOR TRIANGULATE.H ***************************//**********************************************************************/#ifndef TRIANGULATE_H#define TRIANGULATE_H/*****************************************************************//** Static class to triangulate any contour/polygon efficiently **//** You should replace Vector2d with whatever your own Vector   **//** class might be.  Does not support polygons with holes.      **//** Uses STL vectors to represent a dynamic array of vertices.  **//** This code snippet was submitted to FlipCode.com by          **//** John W. Ratcliff ([e-mail]) on July 22, 2000    **//** I did not write the original code/algorithm for this        **//** this triangulator, in fact, I can't even remember where I   **//** found it in the first place.  However, I did rework it into **//** the following black-box static class so you can make easy   **//** use of it in your own code.  Simply replace Vector2d with   **//** whatever your own Vector implementation might be.           **//*****************************************************************/#include <vector>  // Include STL vector class.class Vector2d{public:  Vector2d(float x,float y)  {    Set(x,y);  };  float GetX(void) const { return mX; };  float GetY(void) const { return mY; };  void  Set(float x,float y)  {    mX = x;    mY = y;  };private:  float mX;  float mY;};// Typedef an STL vector of vertices which are used to represent// a polygon/contour and a series of triangles.typedef std::vector< Vector2d > Vector2dVector;class Triangulate{public:  // triangulate a contour/polygon, places results in STL vector  // as series of triangles.  static bool Process(const Vector2dVector &contour,                      Vector2dVector &result);  // compute area of a contour/polygon  static float Area(const Vector2dVector &contour);  // decide if point Px/Py is inside triangle defined by  // (Ax,Ay) (Bx,By) (Cx,Cy)  static bool InsideTriangle(float Ax, float Ay,                      float Bx, float By,                      float Cx, float Cy,                      float Px, float Py);private:  static bool Snip(const Vector2dVector &contour,int u,int v,int w,int n,int *V);};#endif/**************************************************************************//*** END OF HEADER FILE TRIANGULATE.H BEGINNING OF CODE TRIANGULATE.CPP ***//**************************************************************************/#include <stdio.h>#include <stdlib.h>#include <string.h>#include <assert.h>#include "triangulate.h"static const float EPSILON=0.0000000001f;float Triangulate::Area(const Vector2dVector &contour){  int n = contour.size();  float A=0.0f;  for(int p=n-1,q=0; q<n; p=q++)  {    A+= contour[p].GetX()*contour[q].GetY() - contour[q].GetX()*contour[p].GetY();  }  return A*0.5f;}   /*     InsideTriangle decides if a point P is Inside of the triangle     defined by A, B, C.   */bool Triangulate::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));};bool Triangulate::Snip(const Vector2dVector &contour,int u,int v,int w,int n,int *V){  int p;  float Ax, Ay, Bx, By, Cx, Cy, Px, Py;  Ax = contour[V[u]].GetX();  Ay = contour[V[u]].GetY();  Bx = contour[V[v]].GetX();  By = contour[V[v]].GetY();  Cx = contour[V[w]].GetX();  Cy = contour[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[V[p]].GetX();    Py = contour[V[p]].GetY();    if (InsideTriangle(Ax,Ay,Bx,By,Cx,Cy,Px,Py)) return false;  }  return true;}bool Triangulate::Process(const Vector2dVector &contour,Vector2dVector &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.push_back( contour[a] );      result.push_back( contour[b] );      result.push_back( contour[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;    }  }  delete V;  return true;}/************************************************************************//*** END OF CODE SECTION TRIANGULATE.CPP BEGINNING OF TEST.CPP A SMALL **//*** TEST APPLICATION TO DEMONSTRATE THE USAGE OF THE TRIANGULATOR     **//************************************************************************/#include <stdio.h>#include <stdlib.h>#include <string.h>#include <assert.h>#include "triangulate.h"void main(int argc,char **argv){  // Small test application demonstrating the usage of the triangulate  // class.  // Create a pretty complicated little contour by pushing them onto  // an stl vector.  Vector2dVector a;  a.push_back( Vector2d(0,6));  a.push_back( Vector2d(0,0));  a.push_back( Vector2d(3,0));  a.push_back( Vector2d(4,1));  a.push_back( Vector2d(6,1));  a.push_back( Vector2d(8,0));  a.push_back( Vector2d(12,0));  a.push_back( Vector2d(13,2));  a.push_back( Vector2d(8,2));  a.push_back( Vector2d(8,4));  a.push_back( Vector2d(11,4));  a.push_back( Vector2d(11,6));  a.push_back( Vector2d(6,6));  a.push_back( Vector2d(4,3));  a.push_back( Vector2d(2,6));  // allocate an STL vector to hold the answer.  Vector2dVector result;  //  Invoke the triangulator to triangulate this polygon.  Triangulate::Process(a,result);  // print out the results.  int tcount = result.size()/3;  for (int i=0; i<tcount; i++)  {    const Vector2d &p1 = result[i*3+0];    const Vector2d &p2 = result[i*3+1];    const Vector2d &p3 = result[i*3+2];    printf("Triangle %d => (%0.0f,%0.0f) (%0.0f,%0.0f) (%0.0f,%0.0f)\n",i+1,p1.GetX(),p1.GetY(),p2.GetX(),p2.GetY(),p3.GetX(),p3.GetY());  }}