Dissecting Hard Rock Memorabilia and Silverlight Deep Zoom - Part 7

One of the readers asked me if I could post code to center the clicked image on the screen. So here goes...

Update Oct 14, 2008: Removed the example from this post to reduce load time of this page. Please use the example from this post, DeepZoom sample ported to Silverlight 2 Beta 2, to try the functionality.

The example above centers and zooms the clicked image.

Here is the code

msi.MouseLeftButtonUp += delegate(object sender, MouseButtonEventArgs e)
{
    if (mouseButtonPressed && !dragInProgress)
    {
        Point p = this.msi.ElementToLogicalPoint(e.GetPosition(this.msi));
        int subImageIndex = SubImageHitTest(p);
        if (subImageIndex >= 0)
            DisplaySubImageCentered(subImageIndex);

        bool shiftDown = (Keyboard.Modifiers & ModifierKeys.Shift) == ModifierKeys.Shift;
        if (shiftDown)  Zoom(0.5, e.GetPosition(this.msi));
        else            Zoom(2.0, e.GetPosition(this.msi));
    }
    mouseButtonPressed = false;
    dragInProgress = false;
};

void DisplaySubImageCentered(int indexSubImage)
{
    if (indexSubImage < 0 || indexSubImage >= msi.SubImages.Count)
        return;
    
    Rect subImageRect = GetSubImageRect(indexSubImage);
    double msiAspectRatio = msi.ActualWidth / msi.ActualHeight;

    Point newOrigin = new Point(subImageRect.X - (msi.ViewportWidth / 2) + (subImageRect.Width / 2), 
                                subImageRect.Y - ((msi.ViewportWidth / msiAspectRatio) / 2) + (subImageRect.Height / 2));

    msi.ViewportOrigin = newOrigin;
}

int SubImageHitTest(Point p)
{
    for (int i=0; i<msi.SubImages.Count; i++) {
        Rect subImageRect = GetSubImageRect(i);
        if (subImageRect.Contains(p))
            return i;
    }

    return -1;
}

Rect GetSubImageRect(int indexSubImage)
{
    if (indexSubImage < 0 || indexSubImage >= msi.SubImages.Count)
        return Rect.Empty;
    
    MultiScaleSubImage subImage = msi.SubImages[indexSubImage];
    
    double scaleBy = 1 / subImage.ViewportWidth;
    return new Rect(-subImage.ViewportOrigin.X * scaleBy, -subImage.ViewportOrigin.Y * scaleBy, 
                                    1 * scaleBy, (1 / subImage.AspectRatio) * scaleBy);
}