如何在 C# windows 窗体中绘制可缩放图像

Question

所以我正在实现一个可以读取图像平移、缩放和做其他事情的项目。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，出现在图像上的线与我在屏幕上画的线不对应，这意味着它发生了偏移，我知道它是因为图像的重新调整大小和缩放，但是当我在图像上用其原始大小（图像）和平移画线时；我没问题。

这是代码。

首先这里是当我点击浏览并选择图片时如何加载图片

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;
}

然后在我写的 pictureBox_Paint 事件的事件处理程序中：

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);
}

如您所见，调整后的大小不是原始图像大小，我这样做是因为我希望图像显示在图片框控件上集中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;
}
}

这里是鼠标向上事件处理程序

//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绘制并使其与真实图像以及我画线的屏幕相对应 感谢和抱歉发了这么长的帖子，但这个问题让我发疯了。

Answer 1

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

它包含一个SetZoom 函数，可通过缩放自身和矩阵来放大。

它还有一个ScalePoint 函数，可用于根据鼠标事件中收到的像素坐标计算未缩放的坐标。

这个想法是使用Transformation Matrix 来缩放Graphics 对象将在Paint 事件中绘制的任何像素。

我在表单中包含了一些用于测试的代码。

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 );     }

}

这是表单中进行测试的代码：

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));
    }
}

以下是在四种不同缩放设置中绘制几个相同点后的结果； ScaledPictureBox 显然放在AutoScroll-Panel 中。这些线条显示了如何使用常规绘图命令..