Double multiplication giving NaN

I'm trying to use manipulation to rescale a canvas. On debugging the below code it seems that canImage.Width and canImage.Heigh both get set to NaN. I don't understand how a double times a double can give Nan

(width ~ 400 Height ~400 e.scale.y ~-1.5 e.Scale.X ~0.3)

.

    private void viewer_ManipulationCompleted(object sender, System.Windows.Input.ManipulationCompletedEventArgs e)
    {
        if (e.TotalManipulation.Scale.X != 0 && e.TotalManipulation.Scale.Y != 0) {
       开发者_如何学运维     canImage.Width = mainImage.Width * (double)e.TotalManipulation.Scale.X;
            canImage.Height = mainImage.Height * (double)e.TotalManipulation.Scale.Y;
        }
    }

EDIT: Just put a conditional breakpoint in and it seems e.TotalManipulation.Scale.X and e.TotalManipulation.Scale.X are never NaN. Putting the e.TotalManipulation.Scale.X > 0 condition did stop the issue. It looks like setting Height/Width to something less than one just causes them to become NaN rather than just falling over. Thanks for all your help

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Is that negative sign supposed to be there for e.scale.y = -1.5? Setting the height to a negative number may explain your problems.

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If e.TotalManipulation.Scale.X or e.TotalManipulation.Scale.Y are equal to NaN, then the product will be equal to NaN. Try testing using the following instead (since you wouldn't want negative numbers either):

if (e.TotalManipulation.Scale.X > 0 && e.TotalManipulation.Scale.Y > 0)