C# winform实现图片裁剪效果

准备在winform程序里做一个图片剪切功能，一个矩形框 有手柄 可进行调整 对图片进行裁剪。 就像ACDSee那样：

 仔细想了下对图片进行裁剪  裁剪这个过程完全不用我们费心
因为.Net里为我们提供了drawImage这个万能的函数了，msdn里对他的大概解释是 把原图指定矩形区域的像素“画”到目标Image的指定矩形区域

来看看：

//图像裁剪
public Bitmap GetPartOfImage(Bitmap sourceImg, int width, int height, int offsetX, int offsetY)
{
    Bitmap sourceBitmap = sourceImg;
 
    Bitmap resultBitmap = new Bitmap(width, height);
    using (Graphics g = Graphics.FromImage(resultBitmap))
    {
        Rectangle resultRectangle = new Rectangle(0, 0, width, height);
        Rectangle sourceRectangle = new Rectangle(0 + offsetX, 0 + offsetY, width, height);
 
        //万能的drawImage函数，七七八八的参数非常多 普通的图片拉伸 放大 等效果都可以用它来做到。
        //第一个参数：原图（被裁剪的图）
        //第二个参数：目标Image（裁剪后的图）
        //第三个参数：原图被裁剪的区域
        //第四个参数：单位（当然是像素啦）
        g.DrawImage(sourceBitmap, resultRectangle, sourceRectangle, GraphicsUnit.Pixel);
    }
    return resultBitmap;
}

所以说裁剪的过程不需要费心 我们只需要实现那个矩形调整的效果就ok啦。
简而言之效果就是通过鼠标对一个矩形框进行：
在四个角的不同位置进行光标变换、 拖拽、在相应的位置固定某一个边 对矩形进行 上 下 左 右 等八个方向的拉伸。
好解释完了 懂否？调整好后把矩形框的 宽 高 坐标 传到上面的函数进行处理就ok啦。
好 核心的东西全解释完了 该出手了。

为了做得比较通用本人采用了继承自定义控件的方式，因为我是这么想的：
第一 继承了System.Windows.Forms.Control类后OnMouseOver 拖拽那些事件 都可以被天然的捕捉到然后交由自己定义的代码来处理
第二 你需要做的处理就是 通过不同的方式对控件的长宽进行调整 并复写Control类的OnPaint来进行实时的显示
第三 所有的东东都被封装到这个继承的控件里了 所有鼠标事件都与外界无关，这样以后使用更方便不用代码调来调去的 。
只需要在控件里公开一个获取选择区域的方法就可以了

首先是拖拽的效果，他的过程是这样的：在鼠标左键按下时记录当前控件相对于父容器的坐标 也就是this.location属性 还有鼠标的坐标,
鼠标移动时检查如果左键按下 则测算出当前鼠标位置跟原来记录的偏移量， 然后对原来记录的location进行偏移 赋值给this.location 直至鼠标弹起 完成一次拖拽的效果
鼠标左键重新按下并移动的时候重复上述过程：

private Point m_MousePoint;
private Point m_LastPoint;
protected override void OnMouseDown(MouseEventArgs e)
{
    base.OnMouseDown(e);
    this.m_LastPoint = this.Location;
    this.m_MousePoint = this.PointToScreen(e.Location);          
}
 
protected override void OnMouseMove(MouseEventArgs e)
{
    base.OnMouseMove(e);
    if (e.Button == MouseButtons.Left)
    {
        Point t = this.PointToScreen(e.Location);
        Point l = this.m_LastPoint;
        l.Offset(t.X - this.m_MousePoint.X, t.Y - this.m_MousePoint.Y);
        this.Location = l;
    }
}

矩形框上下左右拉伸不用多说了吧 原理嘛大家想想就明白了，onPaint时候矩形的绘制嘛自然是沿着控件的边框绘制就可以了噻
onMouseMove的时候矩形边框的判断嘛自然是根据控件的宽度跟高度加上location来的噻 ，在边框按下鼠标拖拽相应调整控件的宽高跟坐标就行了
好下面是该自定义控件的关键部分代码 包括矩形框手柄以及调整效果：

protected override void OnMouseMove(MouseEventArgs e)
        {
 
            base.OnMouseMove(e);
 
            if (arow != arrowType.none)
            {
                reSize(e);
                return;
            }
 
            if (e.Y <= recArrow[4].Bottom && e.Y >= recArrow[4].Top && e.X >= recArrow[4].Left && e.X <= recArrow[4].Right)//左上
                Cursor = Cursors.SizeNWSE;
            else if (e.Y <= recArrow[5].Bottom && e.Y >= recArrow[5].Top && e.X >= recArrow[5].Left && e.X <= recArrow[5].Right)//左下
                Cursor = Cursors.SizeNESW;
            else if (e.Y <= recArrow[6].Bottom && e.Y >= recArrow[6].Top && e.X >= recArrow[6].Left && e.X <= recArrow[6].Right)//右上
                Cursor = Cursors.SizeNESW;
            else if (e.Y <= recArrow[7].Bottom && e.Y >= recArrow[7].Top && e.X >= recArrow[7].Left && e.X <= recArrow[7].Right)//右下
                Cursor = Cursors.SizeNWSE;
            else if (e.Y <= recArrow[0].Bottom && e.Y >= recArrow[0].Top)//上
                Cursor = Cursors.SizeNS;
            else if (e.Y <= recArrow[1].Bottom && e.Y >= recArrow[1].Top)//下
                Cursor = Cursors.SizeNS;
            else if (e.X >= recArrow[2].Left && e.X <= recArrow[2].Right)//左
                Cursor = Cursors.SizeWE;
            else if (e.X >= recArrow[3].Left && e.X <= recArrow[3].Right)//右
                Cursor = Cursors.SizeWE;
            else
                Cursor = Cursors.SizeAll;
 
 
            if (e.Button == MouseButtons.Left)
            {
                Point t = this.PointToScreen(e.Location);
                Point l = this.m_LastPoint;
 
                if (e.Y <= recArrow[4].Bottom && e.Y >= recArrow[4].Top && e.X >= recArrow[4].Left && e.X <= recArrow[4].Right)//左上
                    arow = arrowType.leftUp;
                else if (e.Y <= recArrow[5].Bottom && e.Y >= recArrow[5].Top && e.X >= recArrow[5].Left && e.X <= recArrow[5].Right)//左下
                    arow = arrowType.leftDown;
                else if (e.Y <= recArrow[6].Bottom && e.Y >= recArrow[6].Top && e.X >= recArrow[6].Left && e.X <= recArrow[6].Right)//右上
                    arow = arrowType.rightUp;
                else if (e.Y <= recArrow[7].Bottom && e.Y >= recArrow[7].Top && e.X >= recArrow[7].Left && e.X <= recArrow[7].Right)//右下
                    arow = arrowType.rightDown;
                else if (e.Y <= recArrow[0].Bottom && e.Y >= recArrow[0].Top)//上
                    arow = arrowType.up;
                else if (e.Y <= recArrow[1].Bottom && e.Y >= recArrow[1].Top)//下
                    arow = arrowType.down;
                else if (e.X >= recArrow[2].Left && e.X <= recArrow[2].Right)//左
                    arow = arrowType.left;
                else if (e.X >= recArrow[3].Left && e.X <= recArrow[3].Right)//右
                    arow = arrowType.right;
                else
                    arow = arrowType.none;
 
 
                l.Offset(t.X - this.m_MousePoint.X, t.Y - this.m_MousePoint.Y);
                if (arow != arrowType.none)
                    reSize(e);
                else
                {
                    this.Location = l;
                    Refresh();//这句很重要立即重绘 不然拖动到时候会出现卡卡 的现象 ，找了半天原因
                }
            }
        }
 
        public void reSize(MouseEventArgs e)
        {
            Point t = this.PointToScreen(e.Location);
            Point l = this.m_LastPoint;
 
            l.Offset(t.X - this.m_MousePoint.X, t.Y - this.m_MousePoint.Y);
 
            switch (arow)
            {
                case arrowType.up:
                    {
                        this.Height = m_Size.Height - (t.Y - this.m_MousePoint.Y);
                        this.Location = new Point(m_LastPoint.X, l.Y);
                        break;
                    }
                case arrowType.down:
                    {
                        this.Height = m_Size.Height + (t.Y - this.m_MousePoint.Y);
                        break;
                    }
                case arrowType.left:
                    {
                        this.Width = m_Size.Width - (t.X - this.m_MousePoint.X);
                        this.Location = new Point(l.X, m_LastPoint.Y);
                        break;
                    }
                case arrowType.right:
                    {
                        this.Width = m_Size.Width + (t.X - this.m_MousePoint.X);
                        break;
                    }
                case arrowType.leftUp:
                    {
                        this.Width = m_Size.Width - (t.X - this.m_MousePoint.X);
                        this.Height = m_Size.Height - (t.Y - this.m_MousePoint.Y);
                        this.Location = new Point(l.X, l.Y);
                        break;
                    }
                case arrowType.leftDown:
                    {
                        this.Width = m_Size.Width - (t.X - this.m_MousePoint.X);
                        this.Height = m_Size.Height + (t.Y - this.m_MousePoint.Y);
                        this.Location = new Point(l.X, m_LastPoint.Y);
                        break;
                    }
                case arrowType.rightUp:
                    {
                        this.Width = m_Size.Width + (t.X - this.m_MousePoint.X);
                        this.Height = m_Size.Height - (t.Y - this.m_MousePoint.Y);
                        this.Location = new Point(m_LastPoint.X, l.Y);
                        break;
                    }
                case arrowType.rightDown:
                    {
                        this.Width = m_Size.Width + (t.X - this.m_MousePoint.X);
                        this.Height = m_Size.Height + (t.Y - this.m_MousePoint.Y);
                        break;
                    }
            }
            this.Refresh();
        }
 
  
 
        public enum arrowType
        {
            up,down,left,right,leftUp,leftDown,rightUp,rightDown,none
        }
 
        public arrowType arow=arrowType.none;
 
        Rectangle []recArrow=new Rectangle[8];//8个手柄
 
        public  Rectangle area ;//选择区域
        public readonly int blank=8;//边距
        protected override void OnPaint(PaintEventArgs e)
        {
            int side = 6;//手柄矩形的边长
             
            recArrow[0] = new Rectangle(new Point(this.Width / 2 - side / 2, blank - side / 2), new Size(side, side));
            recArrow[1] = new Rectangle(new Point(this.Width / 2 - side / 2, this.Height - blank - side / 2), new Size(side, side));
            recArrow[2] = new Rectangle(new Point(blank-side/2 , this.Height / 2 - side/2), new Size(side, side));
            recArrow[3] = new Rectangle(new Point(this.Width-blank - side / 2, this.Height / 2 - side / 2), new Size(side, side));
            recArrow[4] = new Rectangle(new Point(blank - side / 2, blank - side / 2), new Size(side, side));
            recArrow[5] = new Rectangle(new Point(blank - side / 2, this.Height - blank - side / 2), new Size(side, side));
            recArrow[6] = new Rectangle(new Point(this.Width - blank - side / 2, blank - side / 2), new Size(side, side));
            recArrow[7] = new Rectangle(new Point(this.Width - blank - side / 2, this.Height - blank - side / 2), new Size(side, side));
 
            foreach (Rectangle item in recArrow)
                e.Graphics.DrawRectangle(Pens.Red, item);
            area = new Rectangle(new Point(8, 8), new Size(this.Width-8*2, this.Height-8*2));
 
            加上半透明效果看倒是好看了 重绘的时候卡的凶 ，期待有解决方法
            e.Graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
            System.Drawing.Color cor = System.Drawing.Color.FromArgb(50, Color.Red);
            System.Drawing.SolidBrush bsh = new System.Drawing.SolidBrush(cor);
            e.Graphics.FillRectangle(bsh, area);
 
            e.Graphics.DrawRectangle(Pens.Red,area );
        }

 最后还在一个老外的网站上扣了一段羽化效果的代码，可废了俺老大劲儿了。
好了大功告成走走看：

代码下载：C# winform实现图片裁剪效果