void CoerceScale(bool recompute)
{
if (viewport != null && _bitmap != null && _bitmap.PixelHeight != 0 && _bitmap.PixelWidth != 0)
{
var result = CoerceScaleImpl(viewport.ActualWidth, viewport.ActualHeight, _bitmap.PixelWidth, _bitmap.PixelHeight, 0.0);
_minScale = result.Item1;
_coercedScale = _scale = result.Item2;
}
}