边标志法填充多边形

这里不仔细讲原理，只是把我写的算法发出来，跟大家分享下，如果有错误的话，还请大家告诉我，如果写的不好，也请指出来，一起讨论进步。

基本思想: 先用一种特殊的颜色在帧缓冲器中将多边形的边界(水平边界除外)勾画出来，然后将着色的像素点依x坐标递增的顺序两两配对，再将每一对像素所构成的扫描线区间内的所有像素置为填充色。具体分为两个步骤;

(1) 打标记。对多边形的每条边进行直线扫描转换。

(2) 填充。 对每条与多边形相交的扫描线，依从左到右顺序，按“左闭右开”的原则对扫描线上的像素点进行填充。使用一个布尔量inside来指示当前点的状态，若点在多边形内，则inside为真，否则为假。inside初值为假，第当当前访问像素为被打上标记的点时就把inside取反。对未打标记的像素，inside不变。若访问当前像素时，对inside作必要操作后，inside为真，由把该像素置为填充色。

下面是程序：

/*
*	Date: 11/23/2010
*/
#include <GL/glew.h>
#include <GL/freeglut.h>
#include <vector>
#include <iostream>
#include <fstream>
using std::ofstream;
using std::ifstream;
using std::cout;
using std::endl;
ifstream cin ("polypoints.txt");
typedef struct _Point
{int x;int y;
}Point;typedef struct _PolyPoints
{Point * pPoint;						// Pointer to pointsint		n;							// Number of pointsint		yMax;						// Max y of all pointsint		yMin;						// Min y of all pointsint		xMax;						// Max x of all pointsint		xMin;						// Min x of all points
}PolyPoints;PolyPoints g_polyPoints;				// Storage for points of polygons
bool **	g_pbEdgeFlag;					// Edge flag
void inputPoints (void)
{int n;cin>>n;if (n < 3){cout<<"number of points can not be less than 3"<<endl;exit (0);}g_polyPoints.n = n;g_polyPoints.pPoint = new Point[n];g_polyPoints.yMax = INT_MIN;g_polyPoints.yMin = INT_MAX;g_polyPoints.xMax = INT_MIN;g_polyPoints.xMin = INT_MAX;int x, y;for (int i = 0; i < n; ++i){cin>>x>>y;g_polyPoints.pPoint[i].x = x;g_polyPoints.pPoint[i].y = y;if (g_polyPoints.yMax < y){g_polyPoints.yMax = y;}if (g_polyPoints.yMin > y){g_polyPoints.yMin = y;}if (g_polyPoints.xMax < x){g_polyPoints.xMax = y;}if (g_polyPoints.xMin > x){g_polyPoints.xMin = x;}}int xLen = g_polyPoints.xMax - g_polyPoints.xMin + 1;int yLen = g_polyPoints.yMax - g_polyPoints.yMin + 1;g_pbEdgeFlag = new bool *[yLen];for (int i = 0; i < yLen; ++i){g_pbEdgeFlag[i] = new bool [xLen];memset (g_pbEdgeFlag[i], 0, sizeof (bool) * xLen);}
}
// Free the memory
void destroy (void)
{int yLen = g_polyPoints.yMax - g_polyPoints.yMin + 1;for (int i = 0; i < yLen; ++i){delete g_pbEdgeFlag[i];}delete g_pbEdgeFlag;}
void scanConvertLineAndFlag (const Point & p1, const Point & p2)
{int x1 = p1.x;int y1 = p1.y;int x2 = p2.x;int y2 = p2.y;int x, y, dx, dy, e;// k does not existif (x1 == x2){if (y1 < y2){y = y1;glBegin (GL_POINTS);while (y <= y2){glVertex2i (x1, y);// Flag current pointbool bFlag = g_pbEdgeFlag[y-g_polyPoints.yMin][x1-g_polyPoints.xMin];g_pbEdgeFlag[y-g_polyPoints.yMin][x1-g_polyPoints.xMin] = !bFlag;++ y;}glEnd ();} // if (y1 < y2)else{y = y2;glBegin (GL_POINTS);while (y <= y1){glVertex2i (x1, y);// Flag current pointbool bFlag = g_pbEdgeFlag[y-g_polyPoints.yMin][x1-g_polyPoints.xMin];g_pbEdgeFlag[y-g_polyPoints.yMin][x1-g_polyPoints.xMin] = !bFlag;++ y;}glEnd ();}} // if (x1 == x2)else if (y1 == y2) // k = 0{if (x1 < x2){glBegin (GL_POINTS);x = x1;while (x <= x2){glVertex2i (x, y1);++ x;}glEnd ();} // if (x1 < x2)else {x = x2;glBegin (GL_POINTS);while (x <= x1){glVertex2i (x, y1);++ x;}glEnd ();}}else {if (x1 > x2){int temp = x1;x1 = x2;x2 = temp;temp = y1;y1 = y2;y2 = temp;}x = x1;y = y1;dx = x2 - x1;dy = y2 - y1;// k = 1if (dx == dy){glBegin (GL_POINTS);while (x <= x2){glVertex2i (x, y);// Flag current pointbool bFlag = g_pbEdgeFlag[y-g_polyPoints.yMin][x-g_polyPoints.xMin];g_pbEdgeFlag[y-g_polyPoints.yMin][x-g_polyPoints.xMin] = !bFlag;++ x;++ y;}glEnd ();}else if (dx == -dy) // k = -1{glBegin (GL_POINTS);while (x <= x2){glVertex2i (x, y);// Flag current pointbool bFlag = g_pbEdgeFlag[y-g_polyPoints.yMin][x-g_polyPoints.xMin];g_pbEdgeFlag[y-g_polyPoints.yMin][x-g_polyPoints.xMin] = !bFlag;++ x;-- y;}glEnd ();}else if (dy > dx)	// k > 1{glBegin (GL_POINTS);dx <<= 1;e = - dy;dy <<= 1;y = y1 > y2 ? y2 : y1;int maxY = y1 > y2 ? y1 : y2;while (y <= maxY){glVertex2i (x, y);// Flag current pointbool bFlag = g_pbEdgeFlag[y-g_polyPoints.yMin][x-g_polyPoints.xMin];g_pbEdgeFlag[y-g_polyPoints.yMin][x-g_polyPoints.xMin] = !bFlag;++ y;e += dx;if (e > 0){++ x;e -= dy;}}glEnd ();}else if (dy > 0)	// 0 < k < 1{e = -dx;dx <<= 1;dy <<= 1;glBegin (GL_POINTS);while (x <= x2){glVertex2i (x, y);// Flag current pointbool bFlag = g_pbEdgeFlag[y-g_polyPoints.yMin][x-g_polyPoints.xMin];g_pbEdgeFlag[y-g_polyPoints.yMin][x-g_polyPoints.xMin] = !bFlag;++ x;e += dy;if (e > 0){e -= dx;++ y;}}glEnd ();}else if (-dy < dx)	// 0 > k > -1{e = -dx;dx <<= 1;dy <<= 1;glBegin (GL_POINTS);while (x <= x2){glVertex2i (x, y);// Flag current pointbool bFlag = g_pbEdgeFlag[y-g_polyPoints.yMin][x-g_polyPoints.xMin];g_pbEdgeFlag[y-g_polyPoints.yMin][x-g_polyPoints.xMin] = !bFlag;++ x;e += dy;if (e < 0){-- y;e += dx;}}glEnd ();}else if (-dy > dx) // k < -1{e = dy;dx <<= 1;dy <<= 1;glBegin (GL_POINTS);y = y1 > y2 ? y1 : y2;int minY = y1 > y2 ? y2 : y1;while (y >= minY){glVertex2i (x, y);// Flag current pointbool bFlag = g_pbEdgeFlag[y-g_polyPoints.yMin][x-g_polyPoints.xMin];g_pbEdgeFlag[y-g_polyPoints.yMin][x-g_polyPoints.xMin] = !bFlag;e += dx;-- y;if (e > 0){++ x;e += dy;}}glEnd ();}}
}
void init (void)
{glClearColor (0.0f, 0.0f, 0.0f, 1.0f);
}void flagAllEdges (void)
{Point * pPoint = g_polyPoints.pPoint;int n = g_polyPoints.n;for (int i = 0; i < n; ++ i){scanConvertLineAndFlag (pPoint[i], pPoint[(i+1)%n]);}for (int i = 0; i < n; ++i){int j1 = (i+n-1)%n;int j2 = (i+1)%n;if (pPoint[j1].y > pPoint[i].y && pPoint[j2].y > pPoint[i].y ||pPoint[j1].y < pPoint[i].y && pPoint[j2].y < pPoint[i].y){g_pbEdgeFlag[pPoint[i].y - g_polyPoints.yMin][pPoint[i].x - g_polyPoints.xMin] = false;}else{g_pbEdgeFlag[pPoint[i].y - g_polyPoints.yMin][pPoint[i].x - g_polyPoints.xMin] = true;}}
}void edgeFlagFillPolygon (void)
{int xLen = g_polyPoints.xMax - g_polyPoints.xMin + 1;int yLen = g_polyPoints.yMax - g_polyPoints.yMin + 1;int nScanLine = g_polyPoints.yMin;glBegin (GL_POINTS);for (int i = 0; i < yLen; ++i, ++ nScanLine){bool bFlag = false;int nHorizontal = g_polyPoints.xMin;for (int j = 0; j < xLen; ++j, ++ nHorizontal){if (g_pbEdgeFlag[i][j]){bFlag = !bFlag;}while (bFlag){glVertex2i (nHorizontal, nScanLine);++ j;++ nHorizontal;if (g_pbEdgeFlag[i][j]){bFlag = !bFlag;}}}}glEnd ();}void display (void)
{glClear (GL_COLOR_BUFFER_BIT);glLoadIdentity ();glColor3f (1.0f, 0.0f, 0.0f);//flagAllEdges ();// Fill a polygonedgeFlagFillPolygon ();glutSwapBuffers ();
}void reshape (int w, int h)
{glViewport (0, 0, (GLsizei) w, (GLsizei) h);glMatrixMode (GL_PROJECTION);glLoadIdentity ();if (w <= h){gluOrtho2D (-600.0, 600.0, -600.0 * (GLfloat) h / (GLfloat) w, 600.0 * (GLfloat) h / (GLfloat) w);}else{gluOrtho2D (-600.0 * (GLfloat) w / (GLfloat) h,600.0 * (GLfloat) w / (GLfloat) h, -600.0, 600.0);}glMatrixMode (GL_MODELVIEW);glLoadIdentity ();
}
void keyboard (unsigned char key, int x, int y)
{switch (key){case 27: // 'VK_ESCAPE'exit (0);break;default:break;}
}
int main (int argc, char ** argv)
{glutInit (&argc, argv);glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);glutInitWindowSize (600, 600);glutCreateWindow ("Bresenham line");init ();inputPoints ();flagAllEdges ();glutReshapeFunc (reshape);glutDisplayFunc (display);glutKeyboardFunc (keyboard);glutMainLoop ();destroy ();return 0;
}

polypoints.txt中的示例内容如下:
7
30 120
10 70
30 10
60 50
80 10
120 90
70 80