public override bool CanConvertFrom(Type sourceType)
{
return(_converter.CanConvertFrom(sourceType));
}
/// <summary>
/// Convert an ambient light sensor value (in lux) to a corresponding font size
/// for the current lighting conditions based on the default font size (stored in the parameter).
/// </summary>
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
// check to see if the incoming value is a double. This value
// should be bound to the current light value, in lux.
if (value is double)
{
/*
* Approximate table of lux values as they map to human perceived values.
* 0 -> 10 Dark
* 10 -> 300 Dim Indoor
* 300 -> 800 Normal Indoor
* 800 -> 10000 Bright Indoor
* 10000 -> 30000 Overcast Outdoor
* 30000 -> 100000 Direct sunlight
*/
double lightLevelInLux = (double)value;
// check to see if a converter parameter is provided. If it is, that parameter
// is the "base" font size value to convert from.
if (parameter != null)
{
double fontSize = 0.0;
if (parameter is double)
{
// if the font size is a double, then simply cast the double to the font size.
fontSize = (double)parameter;
}
else
{
// see if we can convert from the parameter value, for example the string "12pt"
// will convert to a double fontsize value according to the current DPI settings.
FontSizeConverter fontConverter = new FontSizeConverter();
if (fontConverter.CanConvertFrom(parameter.GetType()))
{
fontSize = (double)fontConverter.ConvertFrom(parameter);
}
else
{
// convert from a default 12pt font value.
fontSize = (double)fontConverter.ConvertFrom("12pt");
}
}
System.Diagnostics.Debug.Assert(fontSize > 0);
// the correlation between light values in lux and human perceived brightness are
// not linear. To fit these two values, we need to convert the values from lux
// into a linear range from 0.0 <-> 1.0. We'll use that value to scale our font size
// up to compensate for the light.
// The calculation of Math.Log10(LightSensorProvider.MaximumSensorReportValue) is shown
// here for clarity's sake. Since this is a constant value, the calculation can be optimized
// into a constant.
double lightLevelRangeValue = Math.Log10(lightLevelInLux) / Math.Log10(LightSensorProvider.MaximumSensorReportValue);
// now that lightLevelRangeValue is between 0.0 <-> 1.0, we can scale the font size.
// since we don't want a zero size font for low light levels, we'll compensate by a constant
// value (0.8) such that we will adjust the font size parameter (stored in fontSize)
// by 80% to 180% (0.8 -> 1.8);
return((FontSizeMultiplierCompensation + lightLevelRangeValue) * fontSize);
}
}
else
{
System.Diagnostics.Debug.Assert(
false,
"Binding value is not a double.",
"Expect value to be a double specifying the light value in lux.");
}
return(value);
}