如何在缩放的图像上绘图？

我有一个图片框Size我的应用程序中为 400X400。这SizeMode图片框的设置为Zoomed。我在图片框中加载了一张700X446的png图像。

我有以下问题，

尽管我沿着红色路径绘制一条黑色直线，但实际上它是沿着加载的图像以透视方式显示的。

我该如何解决这个问题？

P.S.我只想在图像上绘制，而不是整个图片框。

源代码：

 public partial class MainForm : Form
 {
    Bitmap _inputImage = null;
    //Graphics _imageGraphics = null;

    #region ctor
    public MainForm()
    {
        InitializeComponent();

        _inputImage = Bitmap.FromFile(@"E:\cracked.png") as Bitmap;

        this.inputImagePictureBox.Image = _inputImage;
    }
    #endregion

    #region Mouse Up and Down
    Point _startPoint = Point.Empty;

    private void left_MouseDown(object sender, MouseEventArgs e)
    {
        if (e.Button == System.Windows.Forms.MouseButtons.Left)
        {
            _startPoint = e.Location;

            Circle tempCircle = new Circle(_startPoint, 10);

            Bitmap tempImage = (Bitmap)_inputImage.Clone();

            Graphics g = Graphics.FromImage(tempImage);

            tempCircle.Draw(g);

            inputImagePictureBox.Image = tempImage;
        }
    }

    private void pressed_MouseMove(object sender, MouseEventArgs e)
    {
        if (e.Button == System.Windows.Forms.MouseButtons.Left)
        {
            if (_startPoint != e.Location)
            {
                Line tempLine = new Line(_startPoint, e.Location);

                Bitmap tempImage = (Bitmap)_inputImage.Clone();

                Graphics g = Graphics.FromImage(tempImage);

                tempLine.Draw(g);

                inputImagePictureBox.Image = tempImage;
            }
        }
    }

    Bitmap _savedImage;

    private void left__MouseUp(object sender, MouseEventArgs e)
    {
        if (e.Button == System.Windows.Forms.MouseButtons.Left)
        {
            if (_startPoint != e.Location)
            {
                Line tempLine = new Line(_startPoint, e.Location);

                Bitmap tempImage = (Bitmap)_inputImage.Clone();

                Graphics g = Graphics.FromImage(tempImage);

                tempLine.Draw(g);

                _savedImage = tempImage;

                inputImagePictureBox.Image = tempImage;
            }
            else
            {
                Bitmap tempImage = (Bitmap)_inputImage.Clone();
                Graphics g = Graphics.FromImage(tempImage);

                inputImagePictureBox.Image = tempImage;
            }
        }
    } 
}

您需要解决两个问题：

• Clip the Graphics实际面积Image而不是整个PictureBox.ClientArea

• Scale接收和记录鼠标事件时鼠标事件相对于实际图像的坐标，以及当您使用它们在绘图中绘制时再次返回的坐标Paint event.

对于两者我们都需要知道zoom的因素Image;对于剪辑我们​​还需要知道ImageArea为了绘图，我只存储两个鼠标位置。

这是我使用的类级别变量：

PointF mDown = Point.Empty;
PointF mLast = Point.Empty;
float zoom = 1f;
RectangleF ImgArea = RectangleF.Empty;

请注意，我使用floats对于所有人来说，因为我们需要进行一些划分..

首先我们要计算zoom和ImageArea:

void GetImageScaleData(PictureBox pbox)
{
    SizeF sp = pbox.ClientSize;
    SizeF si = pbox.Image.Size;
    float rp = 1f * sp.Width / sp.Height;   // calculate the ratios of
    float ri = 1f * si.Width / si.Height;   // pbox and image

    if (rp > ri)
    {
        zoom = sp.Height / si.Height;
        float width = si.Width * zoom;
        float left = (sp.Width - width) / 2;
        ImgArea = new RectangleF(left, 0, width, sp.Height);
    }
    else
    {
        zoom = sp.Width / si.Width;
        float height = si.Height * zoom;
        float top = (sp.Height - height) / 2;
        ImgArea = new RectangleF(0, top, sp.Width, height);
    }
}

每次新的调用时都应调用此例程Image已加载并且也可以在任何Resizing of the PictureBox:

private void pictureBox1_Resize(object sender, EventArgs e)
{
    GetImageScaleData(pictureBox1);
}

现在需要存储鼠标位置。既然他们一定是调整大小后可重复使用我们需要将它们转换为图像坐标。这个例程可以做到这一点，也可以再次返回：

PointF scalePoint(PointF pt, bool scale)
{
    return scale ? new PointF( (pt.X - ImgArea.X) / zoom, (pt.Y - ImgArea.Y) / zoom)
                 : new PointF( pt.X * zoom + ImgArea.X, pt.Y * zoom + ImgArea.Y);
}

最后我们可以编写代码Paint event

private void pictureBox1_Paint(object sender, PaintEventArgs e)
{
    using (Pen pen = new Pen(Color.Fuchsia, 2.5f) { DashStyle = DashStyle.Dot})
        e.Graphics.DrawRectangle(pen, Rectangle.Round(ImgArea));

    e.Graphics.SetClip(ImgArea);
    e.Graphics.DrawLine(Pens.Red, scalePoint(mDown, false), scalePoint(mLast, false));
}

..和鼠标事件：

private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
{
    mDown = scalePoint(e.Location, true);
}

private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
{
    if (e.Button == System.Windows.Forms.MouseButtons.Left)
    {
        mLast = scalePoint(e.Location, true);
        pictureBox1.Invalidate();
    }
}

对于更复杂的绘图，您可以将坐标存储在List<PointF>并将它们转换回来，就像上面一样......：

List<PointF> points = new List<PointF>();

进而：

e.Graphics.DrawCurve(Pens.Orange, points.Select(x => scalePoint(x, false)).ToArray());