Zoom to Fit to canvas size in C#?

I have a canvas that changes size depending on the users input, i want to hit a button and be able to zoom out to see the whole canvas. Basically i know the height and width of the canvas i just want to zoom in or out so the user can see the whole canvas. I have zoom in and zoom out to work but not sure how do zoom to fit? any thoughts?

February 11th

Thank you for your response, This was great help and i am able to zoom out on the canvas completely. The problem that i am having now is the user has zoom in, and zoom out controls. So if the user zooms in and out and then tries to zoom to fit the canvas the scaling factor will be off, my code is below

This is for the basic zooming in and out on the canvas:

    double ScaleRate = 1.2;

    public void buttonZoomIn_Click(object sender, RoutedEventArgs e)
    {
        st.ScaleX *= ScaleRate;
        st.ScaleY *= ScaleRate;
    }

    public void buttonZoomOut_Click(object sender, RoutedEventArgs e)
  开发者_开发百科  {
        st.ScaleX /= ScaleRate;
        st.ScaleY /= ScaleRate;
    }

The zoom to fit button that i want to press to zoom out completely on the canvas:

private void zoomToFitBt_Click(object sender, RoutedEventArgs e)
    {
        float maxWidthScale = (float)ScrollViewerCanvas.Width / (float)Canvas1.Width;
        float maxHeightScale = (float)ScrollViewerCanvas.Height / (float)Canvas1.Height;
        float scale = Math.Min(maxHeightScale, maxWidthScale);

        if (st.ScaleX > scale || st.ScaleY> scale)
        {
            st.ScaleX *= scale;
            st.ScaleY *= scale;
        }
    }

If i press the zoom to fit button off the start it is fine, but its when the user has done some manual zooming that it messes up. My idea was to maybe every time the user hits the zoom to fit button that it will first go back to its initial state then use the zoom to fit code but not sure about that.

Thanks for your help guys

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Based on what little information given, I will simplify your problem into what I gauge you are asking at a most basic mathmatical level. I think you are asking...

"I have 2 rectangles (the viewport, and the canvas). How do I scale the canvas such that it is as big as possible without exceeding the width or height of the viewport."

this Code will determine how to scale a rectangle in such a way that it will barely fit inside of another rectangle.

Rectangle c = new Rectangle(0, 0, 200, 100); //Canvas Rectancle (assume 200x100)
Rectangle v = new Rectangle(0, 0, 50, 50); //Viewport Rectangle (assume 50x50)

//The maximum scale width we could use
float maxWidthScale = (float)v.Width / (float)c.Width; 

//The maximum scale height we could use
float maxHeightScale = (float)v.Height / (float)c.Height; 

//Use the smaller of the 2 scales for the scaling
float scale = Math.Min(maxHeightScale, maxWidthScale); 

scale = .25 (or 25%) in order to fit using the sample rectangles.