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How to: Create a Zoom Effect

The following example program simulates a zoom effect with two bitmaps of the same size, where the second contains a zoomed center section of the first.

// Define bmp and bmpZoom as 
// global Bitmap variables for your form. 

// Call CreateBitmap and then DefineZoom 
// from your form's consructor. 
void CreateBitmap()
{
    bmp = new Bitmap(75, 75);
    Graphics g = Graphics.FromImage(bmp);
    SolidBrush BlueBrush = new SolidBrush(Color.Blue);
    SolidBrush RedBrush = new SolidBrush(Color.Red);
    Rectangle OuterRect = new Rectangle(0, 0, 200, 200);
    g.FillRectangle(BlueBrush, OuterRect);
    Rectangle InnerRect = new Rectangle(25, 25, 25, 25);
    g.FillRectangle(RedBrush, InnerRect);
    g.Dispose();
}

   private void ZoomImage()
    {
        bmpZoom = new Bitmap(bmp.Width, bmp.Height);
        Graphics g = Graphics.FromImage(bmpZoom);
        int new4W = bmp.Width / 4;
        int new4H = bmp.Height / 4;
        int new2W = bmp.Width / 2;
        int new2H = bmp.Height / 2;
        Rectangle srcRect = new Rectangle(new4W, new4H, new2W, new2H);
        Rectangle dstRect = new Rectangle(0, 0, bmpZoom.Width, bmpZoom.Height);
        g.DrawImage(bmp, dstRect, srcRect, GraphicsUnit.Pixel);
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        e.Graphics.DrawImage(bmp, 0, 0);
        e.Graphics.DrawImage(bmpZoom, 125, 0);
        base.OnPaint(e);
    }

This example requires references to the following namespaces:

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