AET在多边形扫描转换中的使用 Scan conversion polygon and fill red color inside

</pre><pre name="code" class="cpp">

#include<glut.h>
#include <stdio.h>
#include<Windows.h>
/* initialization: */

void myinit(void)
{
/* attributes */
glClearColor(1.0, 1.0, 1.0, 0.0); /* 设置窗口背景颜色为白色 */
glColor3f(1.0, 0.0, 0.0);
glMatrixMode(GL_PROJECTION); /* 指定设置投影参数 */
glLoadIdentity(); /* 调用单位矩阵，去掉以前的投影参数 */
gluOrtho2D(0.0, 100.0, 0.0, 100.0); /* 设置投影参数 */
glMatrixMode(GL_MODELVIEW);
}

void AETFillColor()
{
const int POINTNUM=5; //多边形点数.

/******定义结构体用于活性边表AET和新边表NET***********************************/
typedef struct XET
{
float x;
float dx,ymax;
struct XET* next;
}AET,NET;
/******定义点结构体point******************************************************/
struct point
{
float x;
float y;
}polypoint[POINTNUM]={20,20,40,30,55,90,10,50,20,50};//多边形顶点

/******计算最高点的y坐标**************************************/
int MaxY=0;
int MinY = 100;

int i;
for( i = 0;i < POINTNUM; i++ )
{
if( polypoint[i].y > MaxY )
{
MaxY = polypoint[i].y;
}

if( polypoint[i].y < MinY )
{
MinY = polypoint[i].y;
}

}

/*******初始化AET表，即初始化活跃边表***********************************************************/
AET *pAET = new AET;
pAET->next = NULL;

/******初始化NET表，即初始化边表************************************************************/
NET *pNET[1024];
for( i = MinY;i <= MaxY; i++ )
{
pNET[i] = new NET;
pNET[i]->next = NULL;
}

/******扫描并建立NET表，即建立边表*********************************************************/
for( i = MinY; i <= MaxY; i++ )
{
for( int j = 0;j < POINTNUM; j++ )
{
if( polypoint[j].y == i)
{
if( polypoint[ (j-1+POINTNUM) % POINTNUM ].y > polypoint[j].y )
{
NET *p=new NET;
p->x = polypoint[j].x;
p->ymax = polypoint[ (j-1+POINTNUM) % POINTNUM ].y;
p->dx = ( polypoint[ (j-1+POINTNUM)%POINTNUM ].x-polypoint[j].x ) / ( polypoint[ (j-1+POINTNUM) % POINTNUM ].y - polypoint[j].y );
p->next = pNET[i]->next;
pNET[i]->next = p;
}

if( polypoint[ (j+1+POINTNUM ) % POINTNUM].y > polypoint[j].y )
{
NET *p = new NET;
p->x = polypoint[j].x;
p->ymax = polypoint[ (j+1+POINTNUM) % POINTNUM ].y;
p->dx = ( polypoint[ (j+1+POINTNUM) % POINTNUM ].x-polypoint[j].x ) / ( polypoint[ (j+1+POINTNUM) % POINTNUM ].y- polypoint[j].y );
p->next = pNET[i]->next;
pNET[i]->next = p;
}
}
}
}

/******建立并更新活性边表AET*****************************************************/
for( i = MinY; i <= MaxY; i++ )
{
//计算新的交点x,更新AET********************************************************/
NET *p = pAET->next;
while( p != NULL )
{
p->x = p->x + p->dx;
p = p->next;
}

//更新后新AET先排序*************************************************************/
AET *tq = pAET;
p = pAET->next;
tq->next = NULL;

while( p != NULL )
{
while( tq->next != NULL && p->x >= tq->next->x )
{
tq = tq->next;
}

NET *s = p->next;
p->next = tq->next;
tq->next = p;
p = s;
tq = pAET;
}

//先从AET表中删除ymax==i的结点****************************************/
AET *q = pAET;
p = q->next;
while( p != NULL )
{
if( p->ymax == i)
{
q->next = p->next;
delete p;
p = q->next;
}
else
{
q = q->next;
p = q->next;
}
}

//将NET中的新点加入AET,并用插入法按X值递增排序**********************************/
p = pNET[i]->next;
q = pAET;
while( p != NULL )
{
while( q->next != NULL && p->x >= q->next->x)
{
q = q->next;
}

NET *s = p->next;
p->next = q->next;
q->next = p;
p = s;
q = pAET;
}

/******配对填充颜色***************************************************************/
p = pAET->next;
while( p != NULL && p->next != NULL )
{
for(float j = p->x;j <= p->next->x; j++)
{
glBegin(GL_POINTS);
glVertex3f(j,i,0);
glEnd();
}

p = p->next->next;//考虑端点情况
}
}

NET *phead = NULL;
NET *pnext = NULL;
//释放边表
//释放活跃边表
phead = pAET;
while( phead != NULL )
{
pnext = phead->next;
delete phead;
phead = pnext;
}
}
void display( void )
{
glClear(GL_COLOR_BUFFER_BIT); /*用当前背景色填充窗口 */
glColor3f(1.0f,0.0f,0.0f); /*设置当前的绘图颜色为红色*/
AETFillColor();
glFlush(); /* 清空缓存，执行程序 */
}
int main(int argc, char** argv)
{
glutInit(&argc,argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); /* 初始化窗口显示模式 */
glutInitWindowSize(500,500); /* 设置窗口尺寸 500 x 500 pixel */
glutInitWindowPosition(0,0); /* 设置窗口位置 */
glutCreateWindow("Draw polygon"); /* 命名窗口 */
glutDisplayFunc(display);
myinit();
glutMainLoop();
}

http://blog.csdn.net/xiaowei_cqu/article/details/7712451    AET表