.net – 用Windows Forms缩放大图片

如前所述,图像会非常大,所以我的问题是：是否可以使用默认的PictureBox控件来实现这一点,还是我最好使用第三方控件？如果是这样,请推荐一个包含提供这些功能的控件的库.

正如所承诺的,这是我制作的控件的来源：

/// <summary>
/// A panel used to display an image and zoom into areas of the displayed
/// image.
/// </summary>
public sealed class PictureZoomPanel : Panel
{
    // The image to dispay,set in the Image property
    private Image _image;
    // The current zoom factor
    private float _zoom = 1;
    // The zoom rectangle on the panel.
    private Rectangle _panelZoomRect;
    // _panelZoomRect on the actual image
    private Rectangle? _imageZoomRect;
    // Used in the mouse event handlers
    private bool _mouseDown;
    // The pen used to draw the zoom rectangle
    private Pen _zoomPen;

    /// <summary>
    /// Create a new <see cref="PictureZoomPanel"/>
    /// </summary>
    public PictureZoomPanel()
    {
        // To prevent flickering
        DoubleBuffered = true;
        // To make resizing smoother
        ResizeRedraw = true;
        // Set default zoom pen
        ZoomPen = null;
    }

    /// <summary>
    /// The image to be displayed
    /// </summary>
    [Category("Appearance"),Description("The image to be displayed.")]
    public Image Image
    {
        get { return _image; }
        set
        {
            _image = value;
            ZoomToFit();
        }
    }

    /// <summary>
    /// The pen used to draw the zoom rectangle.
    /// </summary>
    [Category("Appearance"),Description("The pen used to draw the zoom rectangle.")]
    public Pen ZoomPen
    {
        get { return _zoomPen; }
        set {
            _zoomPen = value ?? new Pen(Color.Green,2);
        }
    }

    /// <summary>
    /// Sets the zoom to a value where the whole image is visible.
    /// </summary>
    public void ZoomToFit()
    {
        _imageZoomRect = null;
        _mouseDown = false;
        _zoom = 1;

        // If no image is present,there is nothing further to do
        if (_image == null)
            return;

        var widthZoom = (float) Width / _image.Width;
        var heightZoom = (float) Height / _image.Height;

        // Make sure the whole image is visible
        _zoom = widthZoom < heightZoom ? widthZoom : heightZoom;

        // Force redraw
        Invalidate();
    }

    protected override void OnMouseDown(MouseEventArgs e)
    {
        if (_image == null)
            return;

        _mouseDown = true;
        _panelZoomRect = new Rectangle(e.X,e.Y,0);
    }

    protected override void OnMouseUp(MouseEventArgs e)
    {
        if (_image == null || !_mouseDown)
            return;

        _mouseDown = false;

        // Without this,doubling clicking the control would cause zoom
        if (_panelZoomRect.Height == 0 || _panelZoomRect.Width == 0)
            return;

        // Tell the paint method to zoom
        _imageZoomRect = CalculateImageZoomRectangle();
        _zoom = RecalculateZoom();
    }

    protected override void OnMouseMove(MouseEventArgs e)
    {
        if (_image == null)
            return;

        // This makes sure that the left mouse button is pressed.
        if (e.Button == MouseButtons.Left)
        {
            // Draws the rectangle as the mouse moves
            _panelZoomRect = new Rectangle(
                _panelZoomRect.Left,_panelZoomRect.Top,e.X - _panelZoomRect.Left,e.Y - _panelZoomRect.Top);
        }

        // Force redraw to make sure the zoomRegion is painted
        Invalidate();
    }

    private Rectangle CalculateImageZoomRectangle()
    {
        // Calculate all the coordinates to required to transform
        var topLeft = new Point(_panelZoomRect.X,_panelZoomRect.Y);
        var topRight = new Point(_panelZoomRect.X + _panelZoomRect.Width,_panelZoomRect.Y);
        var bottomLeft = new Point(_panelZoomRect.X,_panelZoomRect.Y - _panelZoomRect.Height);
        var bottomRight = new Point(_panelZoomRect.X + _panelZoomRect.Height,_panelZoomRect.Y - _panelZoomRect.Height);

        var points = new [] { topLeft,topRight,bottomLeft,bottomRight };

        // Converts the points from panel to image position
        var mx = new Matrix(_zoom,_zoom,0);
        mx.Invert();
        mx.TransformPoints(points);

        var rectangleWidth = points[1].X - points[0].X;
        var rectangleHeight = points[0].Y - points[2].Y;

        // _imageZoom != null,means that we are zooming in on an
        // already zoomed in image. We must add the original values
        // to zoom in deeper
        return _imageZoomRect == null
            ? new Rectangle(points[0].X,points[0].Y,rectangleWidth,rectangleHeight)
            : new Rectangle(points[0].X + _imageZoomRect.Value.X,points[0].Y + _imageZoomRect.Value.Y,rectangleHeight);
    }

    private float RecalculateZoom()
    {
        if (!_imageZoomRect.HasValue)
            return _zoom;

        var widthZoom = (float)Width / _imageZoomRect.Value.Width;
        var heightZoom = (float)Height / _imageZoomRect.Value.Height;

        return widthZoom < heightZoom ? widthZoom : heightZoom;
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        if (_image == null)
        {
            OnPaintBackground(e);
            return;
        }

        e.Graphics.Transform = new Matrix(_zoom,0);

        // Turn of interpolation when zoomed
        e.Graphics.InterpolationMode = _imageZoomRect != null 
            ? InterpolationMode.NearestNeighbor 
            : InterpolationMode.Default;

        DrawImage(e);

        if (_mouseDown)
            DrawZoomRectangle(e);

        base.OnPaint(e);
    }

    private void DrawImage(PaintEventArgs e)
    {
        var destRec = !_imageZoomRect.HasValue
            ? new Rectangle(0,_image.Width,_image.Height)
            : new Rectangle(0,_imageZoomRect.Value.Width,_imageZoomRect.Value.Height);

        var sourceRec = !_imageZoomRect.HasValue
            ? new Rectangle(0,_image.Height)
            : _imageZoomRect.Value;

        e.Graphics.DrawImage(_image,destRec,sourceRec.Location.X,sourceRec.Location.Y,sourceRec.Width,sourceRec.Height,GraphicsUnit.Pixel);
    }

    private void DrawZoomRectangle(PaintEventArgs e)
    {
        e.Graphics.Transform = new Matrix();
        e.Graphics.DrawRectangle(_zoomPen,_panelZoomRect);
    }
}