如何在放大的图像上绘图？

Question

Size我的应用程序中有一个400X400 的图片框。图片SizeMode框的 设置为Zoomed。我在图片框中加载了 700X446 的 png 图像。

我有以下问题，

尽管我沿着红色路径画了一条黑色直线，但实际上它是沿着加载的图像在透视之外显示的。

我该如何解决这个问题？

PS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;
            }
        }
    } 
}

Answer 1

你需要解决两个问题：

• 将Graphics区域裁剪到实际Image而不是整个区域PictureBox.ClientArea

• 在接收和记录鼠标事件时将鼠标事件的坐标缩放到实际图像，并在使用它们在Paint事件中绘制时再次返回。

对于两者，我们都需要知道 的缩放系数Image；对于剪辑，我们还需要知道，ImageArea而对于绘图，我只存储了两个鼠标位置。

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floatsfor all，因为我们需要做一些划分..

首先，我们将计算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Image加载新内容时以及调整以下内容的大小时，都应调用此例程PictureBox：

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

现在需要存储鼠标位置。由于它们在调整大小后必须是可重用的，因此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);
}

最后我们可以对Paint事件进行编码

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>其中并将它们转换回来，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());