Function get_ticks_internal 

fn get_ticks_internal(
    viewport: &Viewport,
    timescale: &TimeScale,
    frame_width: f32,
    text_size: f32,
    wanted_timeunit: &TimeUnit,
    time_format: &TimeFormat,
    density: f32,
    num_timestamps: &BigInt,
) -> Vec<(String, f32)>

Get suitable tick locations for the current view port. The method is based on guessing the length of the time string and is inspired by the corresponding code in Matplotlib.