如何不用Windows自带的画椭圆函数画椭圆

Question

如何不用Windows自带的画椭圆函数画椭圆

Answer 1

/////////////////////////////////////////////////////////////////////////////
// Draw a ellipse mid point algorthism
/////////////////////////////////////////////////////////////////////////////
void CGraphicsView::midleEllipse(int xCenter, int yCenter, int Rx, int Ry, HDC dc)
{
int Rx2 = Rx*Rx;
int Ry2 = Ry*Ry;
int twoRx2 = 2*Rx2;
int twoRy2 = 2*Ry2;
int p;
int x=0;
int y=Ry;
int px = 0;
int py = twoRx2*y;
SetPixel(dc,xCenter+x,yCenter+y,RGB(255,0,0));
SetPixel(dc,xCenter-x,yCenter+y,RGB(255,0,0));
SetPixel(dc,xCenter+x,yCenter-y,RGB(255,0,0));
SetPixel(dc,xCenter-x,yCenter-y,RGB(255,0,0));
//Region 1
p = (int)(Ry2-Rx2*Ry+0.25*Rx2);
while(px<py)
{
x++;
px+=twoRy2;
if(p<0)
p+=Ry2+px;
else
{
y--;
py-=twoRx2;
p+=Ry2+px-py;
}
SetPixel(dc,xCenter+x,yCenter+y,RGB(255,0,0));
SetPixel(dc,xCenter-x,yCenter+y,RGB(255,0,0));
SetPixel(dc,xCenter+x,yCenter-y,RGB(255,0,0));
SetPixel(dc,xCenter-x,yCenter-y,RGB(255,0,0));
}
//Region 2
p = (int)(Ry2*(x+0.5)*(x+0.5)+Rx2*(y-1)*(y-1)-Rx2*Ry2);
while(y>0)
{
y--;
py-=twoRx2;
if(p>0)
p+=Rx2-py;
else
{
x++;
px+=twoRy2;
p+=Rx2-py+px;
}
SetPixel(dc,xCenter+x,yCenter+y,RGB(255,0,0));
SetPixel(dc,xCenter-x,yCenter+y,RGB(255,0,0));
SetPixel(dc,xCenter+x,yCenter-y,RGB(255,0,0));
SetPixel(dc,xCenter-x,yCenter-y,RGB(255,0,0));
}}

Answer 2

/////////////////////////////////////////////////////////////////////////////
// Draw a circle
/////////////////////////////////////////////////////////////////////////////
void circleMidpoint(int xCenter,int yCenter,int radius,HDC dc)
{
int x = 0;
int y = radius;
int p=1-radius;
while(x<y)
{
x++;
if(p<0)
{
p+=2*x+1;
}
else
{
y--;
p+=2*(x-y)+1;
}
SetPixel(dc,xCenter+x,yCenter+y,RGB(255,0,0));
SetPixel(dc,xCenter-x,yCenter+y,RGB(255,0,0));
SetPixel(dc,xCenter+x,yCenter-y,RGB(255,0,0));
SetPixel(dc,xCenter-x,yCenter-y,RGB(255,0,0)); SetPixel(dc,xCenter+y,yCenter+x,RGB(255,0,0));
SetPixel(dc,xCenter-y,yCenter+x,RGB(255,0,0));
SetPixel(dc,xCenter+y,yCenter-x,RGB(255,0,0));
SetPixel(dc,xCenter-y,yCenter-x,RGB(255,0,0));
}
}