#include "stdafx.h"
#include "suanfa.h"

//在指定的pDC設備中，畫多邊形
bool CGraphics::DrawPloyon(CDC* pDC)
{
	if(PointCount < 3)
		return false;
	//若多邊形小于三個點則返回

	pDC->MoveTo(Point[0]);
	for(int i=1;i<PointCount;i++)
	{	
		pDC->LineTo(Point[i]);
	}
	pDC->LineTo(Point[0]);
	//在pDC中畫出多邊形
     return true;
}

bool CGraphics::CutRect(CRect rect)
{
	CPoint rectPoint[4];
	rectPoint[0].x = rect.left;
	rectPoint[0].y = rect.top;
	rectPoint[1].x = rect.right;
	rectPoint[1].y = rect.top;
	rectPoint[3].x = rect.left;
	rectPoint[3].y = rect.bottom;
	rectPoint[2].x = rect.right;
	rectPoint[2].y = rect.bottom;
	//獲取裁減矩形的四個點的坐標，第一個點為左上，第二個點為右上，第三個點為右下，第四個點為左下
	int i;
	CArray<CPoint,CPoint&> myArray;//裁減后，保存的多邊形的依次各點的坐標
	for(int rectNum=0;rectNum<4;rectNum++)
	{
		//對裁減矩形的四條邊進行循環
		for(i=0;i<PointCount;i++)
		{
			//對每條邊進行循環
			CPoint PointCross;
			int beforeI=BeforeIndex(i),afterI=AfterIndex(i);
			int afterrectNum = ((rectNum == 3)?0:rectNum+1);
			//判斷是否跟線段相交
			if(InterCross(Point[beforeI],Point[i],rectPoint[rectNum],rectPoint[afterrectNum],PointCross))
			{
				if(PointCross==Point[i])
				{
					myArray.Add(Point[i]);//交點在線段頂點上，直接添加頂點坐標在保存多邊形的數組中
				}
				else 
					if(PointCross==Point[beforeI])
					{
						if(IsInSquareRgn(rect,Point[i],rectNum))
							myArray.Add(Point[i]);//判斷是否可視，若是，則添加點坐標
					}
					else
					{
						myArray.Add(PointCross);//跟線段相交，但交點不在頂點上，添加交點坐標
						if(IsInSquareRgn(rect,Point[i],rectNum))
							myArray.Add(Point[i]);//判斷是否可視，若是，則添加點坐標

					}
					
			}
			else
				if(IsInSquareRgn(rect,Point[i],rectNum))
					myArray.Add(Point[i]);//線段不相交，但需判斷是否可視，若是，則添加點坐標
			
		}
		PointCount=myArray.GetSize();
		if(Point)
			delete Point;
		Point = new CPoint[PointCount];
		for(i=0;i<PointCount;i++)
			Point[i]=myArray.GetAt(i);//重新賦予點坐標的值
		myArray.RemoveAll();
	}
	return true;
}

bool CGraphics::InterCross(CPoint objectP1,CPoint objectP2,CPoint scanP1,CPoint scanP2,CPoint& coordinate)
{
	//objectP1、objectP2是一條線段的頂點坐標，而scanP1、scanP2是另一條線段的頂點坐標
	if(objectP1 == objectP2)
		return false;//若objectP1、objectP2相等，則構不成線段，退出
	if(scanP1 == scanP2)
		return false;//若scanP1、scanP2等，則構不成線段，退出
	if( ( objectP1.y - objectP2.y ) * ( scanP1.x - scanP2.x )
		== ( scanP1.y - scanP2.y ) * ( objectP1.x - objectP2.x))
	{
		//對斜率相等的情況下的處理
		if((objectP1.y-objectP2.y)*(scanP1.x-objectP1.x)==(objectP1.x-objectP2.x)*(scanP1.y-objectP1.y))
		{
			//判斷兩條線段是不是同一條線段
			coordinate=objectP2;
			return true;
		}
		else
			return false;
	}
	if(objectP1.x == objectP2.x)
	{
		//當第一條線段斜率不存在時，處理辦法
		double x,y;
		x = objectP1.x;
		y = (scanP1.y-scanP2.y)*1.0/(scanP1.x-scanP2.x)*(objectP1.x-scanP1.x)+scanP1.y;
		y = (float)((int)(y+0.5));
		if(((objectP1.y-y)*(y-objectP2.y)>=0) && ((objectP1.x-x)*(x-objectP2.x)>=0))
		{
			//判斷交點是不是在該兩條線段上
			coordinate.x = objectP1.x;
			coordinate.y = (int)(y+0.5);
			return true;
		}
		return false;
	}
	else
	{
		if(scanP1.x == scanP2.x)
		{
			//當第二條線段斜率不存在時，處理辦法
			double x,y;
			x = scanP1.x;
			y = (objectP1.y-objectP2.y)*1.0/(objectP1.x-objectP2.x)*(scanP1.x-objectP1.x)+objectP1.y;
			y = (float)((int)(y+0.5));
			if(((objectP1.y-y)*(y-objectP2.y)>=0) && ((objectP1.x-x)*(x-objectP2.x)>=0))
			{
				//判斷交點是不是在該兩條線段上
				coordinate.x = scanP1.x;
				coordinate.y = (int)(y+0.5);
				return true;
			}
			return false;
		}
		else
		{
			//兩條線段斜率都存在時的處理辦法
			double k1,k2;
			k1 = ( objectP1.y - objectP2.y ) * 1.0 / ( objectP1.x - objectP2.x);
			k2 = ( scanP1.y - scanP2.y ) * 1.0 / ( scanP1.x - scanP2.x );
			//k1,k2為計算的兩線段的斜率
			double x,y;
			x = (scanP1.y-objectP1.y-k2*scanP1.x+k1*objectP1.x)/(k1-k2);
			y = (k1*k2*scanP1.x-k1*k2*objectP1.x+k2*objectP1.y-k1*scanP1.y)/(k2-k1);
			x=(float)((int)(x+0.5));
			y = (float)((int)(y+0.5));

			if(((objectP1.y-y)*(y-objectP2.y)>=0) && ((objectP1.x-x)*(x-objectP2.x)>=0))
			{
				//判斷交點是不是在該兩條線段上
				coordinate.x = (int)(x+0.5);
				coordinate.y = (int)(y+0.5);
				return true;
			}
			return false;
		}
	}
	return true;
}

bool CGraphics::IsInSquareRgn(CRect rect,CPoint Point,int flag)
{
	//對多邊形裁減時，判斷線段端點是否在可視一側，判斷就是直接判斷點坐標的關系
	switch(flag) 
	{
	case 0:
		if(Point.y > rect.top)
			return true;
		else 
			return false;
		break;
	case 1:
		if(Point.x < rect.right)
			return true;
		else 
			return false;
		break;
	case 2:
		if(Point.y < rect.bottom)
			return true;
		else 
			return false;
		break;
	case 3:
		if(Point.x > rect.left)
			return true;
		else 
			return false;
		break;
	default:
		break;
	}
	return true;
}