Panel Drawing zoom in C#

Question

I have a Form that contain a panel, and in this panel I draw shapes, like rectangles and circles, I need to zoom into this shapes, I saw couple options but most of them usin

Answer 1

Here is a way to scale the drawing by scaling the Graphics object:

private void panel1_Paint(object sender, PaintEventArgs e)
{
    Graphics g = e.Graphics;
    g.ScaleTransform(zoom, zoom);

    // some demo drawing:
    Rectangle rect = panel1.ClientRectangle;
    g.DrawEllipse(Pens.Firebrick, rect);
    using (Pen pen = new Pen(Color.DarkBlue, 4f)) g.DrawLine(pen, 22, 22, 88, 88);

}

Here we store the zoom level:

float zoom = 1f;

Here we set it and update the Panel:

private void trackBar1_Scroll(object sender, EventArgs e)
{
   // for zooming between, say 5% - 500%
   // let the value go from 50-50000, and initialize to 100 !
    zoom = trackBar1.Value / 100f;  
    panel1.Invalidate();
}

Two example screenshots:

Note how nicely this scales the Pen widths as well. Turning on antialiasing would be a good idea..: g.SmoothingMode = SmoothingMode.AntiAlias;

Answer 2

Since you're drawing from scratch, couldn't you resize you drawing base on zoom factor?

You could multiply your drawing dimensions by your zoom factor. Assuming your zoom factor would be:

• 0.5 for 50 % zoom (which would reduce the drawing size)
• 1.0 for 100% (Real size)
• 1.5 for 150 % (bigger size), you could calc the width this way:

object.Width = originalWidth * zoomFactor;