如何在 C# windows 窗体中在可缩放图像上绘图

Question

所以我正在实现一个可以读取图像的项目，平移它，缩放它并做其他事情......一切都很顺利，直到我尝试用鼠标右键实现绘图。

问题是当我画一条线时，图像上出现的线与我在屏幕上画的线不对应，这意味着它发生了移位，并且我知道它是因为图像的大小和缩放而改变的，但是当我绘制时图像上的线条以其原始尺寸（图像）和平移；我没有问题。

这是代码。

首先这是我单击浏览并选择图像时加载图像的方式

Myimage = new Bitmap(ImagePath);
resized = myImage.Size;
imageResize();
pictureBox.Paint += new    System.Windows.Forms.PaintEventHandler(this.pictureBox_Paint);
                pictureBox.Invalidate();

imageResize 函数执行以下操作：

void imageResize()
{     
//calculated the size to fit the control i will draw the image on   
 resized.Height = someMath;
 resized.Width = someMath;
}

然后在 pictureBox_Paint 事件的事件处理程序中我写道：

private void pictureBox_Paint(object sender,      System.Windows.Forms.PaintEventArgs e)
{
// Create a local version of the graphics object for the PictureBox.
Graphics PboxGraphics = e.Graphics;
PboxGraphics.DrawImage(myImage, imageULcorner.X, imageULcorner.Y,     resized.Width, resized.Height);
}

正如您所看到的，调整后的尺寸不是原始图像尺寸，我这样做是因为我希望图像集中显示在图片框控件上并填充，现在下一部分是我的问题开始的地方

我必须使用鼠标右键在图像上画线，所以我实现了 pictureBox_MouseDown 和 pictureBox_MouseUp 事件处理程序

// mouse down event handler
private void pictureBox_MouseDown(object sender, MouseEventArgs e)
{
else if (mouse.Button == MouseButtons.Right)
{
mouseDown = mouse.Location;
mouseDown.X = mouseDown.X - imageULcorner.X;
mouseDown.Y = mouseDown.Y - imageULcorner.Y;
draw = true;
}
}

这是鼠标按下事件处理程序

//Mouse UP
private void pictureBox_MouseUp(object sender, MouseEventArgs e)
{
else if (mouse.Button == MouseButtons.Right)
{
if (draw)
 {
mouseLocationNow.X = mouse.X - imageULcorner.X;
mouseLocationNow.Y = mouse.Y - imageULcorner.Y;
//
// get graphics object of the image ( the original not the resized)
// as the resized image only appears when i draw on the graphics of the
// pictureBox control
// i know the problem lies here but how can i fix it
//
Graphics image = Graphics.FromImage(myImage);
Pen pen = new Pen(Color.Red, 2);
image.DrawLine(pen, mouseLocationNow, mouseDown);
pictureBox.Invalidate();
}
draw = false;
}

所以最后我希望能够在调整大小的图像上进行绘制，并使其与真实图像以及我画线的屏幕相对应，感谢并抱歉发了这么长的帖子，但这个问题一直让我发疯。

Answer 1

这是一个PictureBox子类，它不仅支持将缩放应用到Image您在其表面上绘制的图形。

它包括SetZoom通过缩放自身和矩阵来放大的功能。

它还具有一个ScalePoint可用于根据鼠标事件中收到的像素坐标计算未缩放坐标的函数。

这个想法是使用 aTransformation Matrix来缩放Graphics对象在事件中绘制的任何像素Paint。

我为测试表单添加了一些代码。

public partial class ScaledPictureBox : PictureBox
{
    public Matrix ScaleM { get; set; }

    float Zoom { get; set; }
    Size ImgSize { get; set; }

    public ScaledPictureBox()
    {
        InitializeComponent();
        ScaleM = new Matrix();
        SizeMode = PictureBoxSizeMode.Zoom;
    }

    public void InitImage()
    {
        if (Image != null)
        {
            ImgSize = Image.Size;
            Size = ImgSize;
            SetZoom(100);
        }
    }

    public void SetZoom(float zoomfactor)
    {
        if (zoomfactor <= 0) throw new Exception("Zoom must be positive");
        float oldZoom = Zoom;
        Zoom = zoomfactor / 100f;
        ScaleM.Reset();
        ScaleM.Scale(Zoom , Zoom );
        if (ImgSize != Size.Empty) Size = new Size((int)(ImgSize.Width * Zoom), 
                                                   (int)(ImgSize.Height * Zoom));

    }

    public PointF ScalePoint(PointF pt)
    {   return new PointF(pt.X / Zoom , pt.Y / Zoom );     }

}

以下是表单中执行测试的代码：

public List<PointF> somePoints = new List<PointF>();

private void scaledPictureBox1_MouseClick(object sender, MouseEventArgs e)
{
    somePoints.Add(scaledPictureBox1.ScalePoint(e.Location) );
    scaledPictureBox1.Invalidate();
}

private void scaledPictureBox1_Paint(object sender, PaintEventArgs e)
{
    // here we apply the scaling matrix to the graphics object:
    e.Graphics.MultiplyTransform(scaledPictureBox1.ScaleM);
    using (Pen pen = new Pen(Color.Red, 10f))
    {
        PointF center = new PointF(scaledPictureBox1.Width / 2f, 
                                   scaledPictureBox1.Height / 2f);
        center = scaledPictureBox1.ScalePoint(center);
        foreach (PointF pt in somePoints)
        {
            DrawPoint(e.Graphics, pt, pen);
            e.Graphics.DrawLine(Pens.Yellow, center, pt);
        }
    }
}

public void DrawPoint(Graphics G, PointF pt, Pen pen)
{
    using (SolidBrush brush = new SolidBrush(pen.Color))
    {
        float pw = pen.Width;
        float pr = pw / 2f;
        G.FillEllipse(brush, new RectangleF(pt.X - pr, pt.Y - pr, pw, pw));
    }
}

以下是绘制几个点后的结果，在四种不同的缩放设置下显示相同的点；显然被ScaledPictureBox放置在AutoScroll-Panel. 这些线条显示了如何使用常规绘图命令。