为什么在这里需要两次绘制椭圆函数Ellipse(...)? [英] Why function Ellipse(...) are needed twice here to draw an ellipse?

问题描述

MFC: 我读了这段绘制椭圆(不是实心内部)的代码，但是我不明白为什么这里需要两次函数"pDC-> Ellipse(...)"? (sol == 0，和do_what == DRAW_ELLIPSE)

MFC: I read this code which is to draw an ellipse (not solid interior), but I cannot understand why function "pDC->Ellipse(...)" is needed twice here? (sol == 0, and do_what==DRAW_ELLIPSE)

void CMy078207017Dlg::OnLButtonUp(UINT nFlags, CPoint point) 
{
        flag = 0;
    end = point;
    assist = point;
    if(p != NULL)
    {
        CDC* pDC = GetDC();
        CPen pen;
        CBrush brush;
        getpen(pen, pDC, col, bol);
        if(do_what >= DRAW_LINE && do_what <= DRAW_RRECT)
        {
            p->p[0] = start;
            p->p[1] = end;
        }

        if(sol == 1)
        {
            getbrush(brush, pDC, col);
        }

        if(do_what == DRAW_LINE)
        {
            pDC->MoveTo(start);
            pDC->LineTo(end);
        }
        else
        {
            if(do_what == DRAW_ELLIPSE || do_what == DRAW_CIRCLE)
            {

                assist = start;
                if(do_what == DRAW_CIRCLE)
                {
                    assist.y = end.y - end.x + start.x;
                }


                pDC->SetROP2(R2_NOT);
                pDC->Ellipse(start.x, assist.y, end.x, end.y);


                pDC->SetROP2(R2_COPYPEN);
                if(sol == 0)
                {
                    pDC->SelectStockObject(NULL_BRUSH);
                }
                pDC->Ellipse(start.x, assist.y, end.x, end.y);


                end = point;
            }

        }
        ReleaseDC(pDC);
    }
    CDialog::OnLButtonUp(nFlags, point);
}

如果我删除对pDC-> Ellipse(...)的第一个调用，则椭圆内部将是黑色实心的. 如果我删除对pDC-> Ellipse(...)的第二次调用，则椭圆将永远不会绘制，但是当鼠标左键向上时椭圆会消失.

If I remove the first call to pDC->Ellipse(...), the ellipse will be black solid inside. If I remove the second call to pDC->Ellipse(...), the ellipse will never be drawn but disappears when left mouse button is up.

对话框: 移动鼠标时: 鼠标移动(笔为绿色)

the dialog: when moving mouse: mouse moving(the pen is green)

当鼠标按钮弹出时: 鼠标按钮弹出(笔为绿色)

when mouse button pops: mouse button pops(the pen is green)

此外，如果我使用CBrush是什么颜色 "CBrush画笔； pDC-> Ellipse(start.x，assist.y，end.x，end.y);"

Besides, what color of CBrush is if I use "CBrush brush; pDC->Ellipse(start.x,assist.y,end.x,end.y);"

当涉及到矩形时，该策略可能会更清晰:

the strategy may be more clear when it comes to rectangle:

             ...
    else if(do_what==DRAW_RECT||do_what==DRAW_RRECT){

            pDC->SetROP2(R2_NOT);
            if(do_what==DRAW_RECT)
            {
                pDC->Rectangle(start.x,start.y,end.x,end.y);
            }
            else if(do_what==DRAW_RRECT)
            {
                pDC->RoundRect(start.x,start.y,end.x,end.y,20,20);
            }


            pDC->SetROP2(R2_COPYPEN);
            if(sol==0)
            {   
                pDC->SelectStockObject(NULL_BRUSH);
            }
            if(do_what==DRAW_RECT)
            {
                pDC->Rectangle(start.x,start.y,point.x,point.y);
            }
            else if(do_what==DRAW_RRECT)
            {
                pDC->RoundRect(start.x,start.y,point.x,point.y,20,20);
            }
            end=point;
        } 
            ...

推荐答案

我终于摆脱了麻烦: 其他地方的代码:

I finally get out of the trouble: codes elsewhere:

void CDraw2009303476Dlg::OnMouseMove(UINT nFlags, CPoint point) 
{
    if(flag == 1)   
    {
        CDC* pDC = GetDC();
        CPen pen;
        CBrush brush;
        getPen(pen, pDC, col, bol);

        if(sol == 1)
        {
            getBrush(brush, pDC, col);
        }
        if(type >= DRAW_LINE && type <= DRAW_RRECT)
        {
            pDC->SetROP2(R2_NOT);
            if(type == DRAW_LINE)
            {
                p->drawLine(point, pDC);
            }
            else if(type == DRAW_ELLIPSE)
            {
                p->drawEllipse(point, pDC);
            }
            else if(type == DRAW_CIRCLE)
            {
                p->drawEllipse(point, pDC, 1);
            }
            else if(type == DRAW_RECT)
            {
                p->drawRect(point, pDC);
            }
            else if(type == DRAW_RRECT)
            {
                p->drawRect(point, pDC, 1);
            }
        }
        ReleaseDC(pDC);
    }
    CDialog::OnMouseMove(nFlags, point);
}

因此，策略是:使用"pDC-> SetROP2(R2_NOT);"一次，然后"p-> drawEllipse(point，pDC，1);"在同一位置两次保存原始像素以获得线条画效果. 最后需要调用"pDC-> SetROP2(R2_COPYPEN); p-> drawEllipse(point，pDC，1)"，这才是我们真正看到省略号的地方. 谢谢您的所有帮助.

So, the strategy is: Using "pDC->SetROP2(R2_NOT);" once and "p->drawEllipse(point, pDC, 1);" twice in the same place to save the original pixels to get the line-drawing effects. And the final call to "pDC->SetROP2(R2_COPYPEN); p->drawEllipse(point, pDC, 1)" is what we really need to see the ellipsis. Thank you for all your helps.

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