struct TemperatureFunction<T> where T: NoiseFn<f64, 2> {
    sea_level: f64,
    max_elevation_meters: f64,
    celsius_loss_per_thousand_meters: f64,
    map_height: f64,
    source: T
}
impl<T> TemperatureFunction<T> where T: NoiseFn<f64, 2> {
    fn new(source: T, map_height: f64) -> TemperatureFunction<T> {
        TemperatureFunction {
            sea_level: 0.5,
            max_elevation_meters: 8000.0,
            celsius_loss_per_thousand_meters: 5.0,
            source,
            map_height
        }
    }
}
impl<T> NoiseFn<f64, 2> for TemperatureFunction<T> where T: NoiseFn<f64, 2> {
    fn get(&self, point: [f64; 2]) -> f64 {
        let latitude = (point[1] - self.map_height / 2.0).abs() / self.map_height * 0.9;
        let base_temp_from_latitude = 35.0 - (latitude*60.0);
        // Anything below 0.5 is below sea level.
        let elevation_above_sea_level = self.source.get(point).max(self.sea_level) - self.sea_level;
        let potential_loss_per_meter_in_celsius = self.max_elevation_meters  * self.celsius_loss_per_thousand_meters / 1000.0;
        let total_elevation_temp_loss_in_celsius = (elevation_above_sea_level / (1.0 - self.sea_level)) * potential_loss_per_meter_in_celsius;
        base_temp_from_latitude - total_elevation_temp_loss_in_celsius
    }
}