Я должен отобразить большое изображение в приложении Windows Forms. Пользователь должен иметь возможность отметить область изображения, которую затем следует увеличить, как в примере, показанном ниже.
Как упоминалось ранее, изображение будет довольно большим, поэтому мой вопрос: возможно ли добиться этого с помощью элемента управления PictureBox по умолчанию или лучше использовать сторонний элемент управления? Если это так, пожалуйста, порекомендуйте библиотеку, которая содержит элемент управления, который предлагает эти функции.
Как и было обещано, вот источник управления, который я сделал:
/// <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, 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, 0, 0, _zoom, 0, 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,
rectangleWidth,
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, 0, _zoom, 0, 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, 0, _image.Width, _image.Height)
: new Rectangle(0, 0, _imageZoomRect.Value.Width,
_imageZoomRect.Value.Height);
var sourceRec = !_imageZoomRect.HasValue
? new Rectangle(0, 0, _image.Width, _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);
}
}