PictureBox Zoom Mode Effect With Graphics Object

问题:

When you load an image into a PictureBox there is a zoom for the image placement, how do I achieve that same effect with a graphics object?

回答1:

I think you mean you want to draw some Image yourself in a Rectangle and using some Graphics object like as the PictureBox renders its Image in Zoom mode. Try the following code. I suppose you want to draw the Image on a Form, the drawing code should be added in a Paint event handler of your form:

//The Rectangle (corresponds to the PictureBox.ClientRectangle)
//we use here is the Form.ClientRectangle
//Here is the Paint event handler of your Form1
private void Form1_Paint(object sender, EventArgs e){
  ZoomDrawImage(e.Graphics, yourImage, ClientRectangle);
}
//use this method to draw the image like as the zooming feature of PictureBox
private void ZoomDrawImage(Graphics g, Image img, Rectangle bounds){
  decimal r1 = (decimal) img.Width/img.Height;
  decimal r2 = (decimal) bounds.Width/bounds.Height;
  int w = bounds.Width;
  int h = bounds.Height;
  if(r1 > r2){
    w = bounds.Width;
    h = (int) (w / r1);
  } else if(r1 < r2){
    h = bounds.Height;
    w = (int) (r1 * h);
  }
  int x = (bounds.Width - w)/2;
  int y = (bounds.Height - h)/2;
  g.DrawImage(img, new Rectangle(x,y,w,h));
}

To test it on your form perfectly, you should also have to set ResizeRedraw = true and enable DoubleBuffered:

public Form1(){
  InitializeComponent();
  ResizeRedraw = true;
  DoubleBuffered = true;
}