public static string Virtualise(this string source, TextScrollInfo scroll)
{
if (scroll == null || scroll.TotalChars == 0)
return source;
return new string(source.Skip(scroll.FirstIndex).Take(scroll.TotalChars).ToArray());
}
public static IEnumerable<DisplayText> Virtualise(this IEnumerable<DisplayText> source, TextScrollInfo scroll)
{
var items = source.AsArray();
if (scroll == null || scroll.TotalChars == 0)
return items;
// var list = new List<DisplayText>(items.Length);
int lastIndex = scroll.FirstIndex + scroll.TotalChars;
var displayBounds = items.Aggregate(new List<DisplayWithIndex>(), (state, latest) =>
{
if (state.Count == 0)
{
state.Add( new DisplayWithIndex(latest, 0));
}
else
{
var last = state.Last();
state.Add(new DisplayWithIndex(latest, last.StartIndex + last.Text.Length));
}
return state;
}).ToArray();
var result = displayBounds
.Select(item =>
{
if (item.Inbounds(scroll.FirstIndex, lastIndex))
{
//clip it and yield
return item.Clip(scroll.FirstIndex, lastIndex);
}
return null;
}).Where(item => item != null)
.ToArray();
return result;
}