private void GetTopAndBottomLineNums(FastColoredTextBox tb, out int top, out int bot)
{
int iTopLine = tb.YtoLineIndex();
int iLine = iTopLine;
int countVisibleLines = tb.ClientSize.Height / tb.CharHeight;
Line line = tb.GetRealLine(iLine);
while (line.Unavaliable && iLine > 0) {
iLine--;
line = tb.GetRealLine(iLine);
}
top = Math.Max(line.LineNo - 1, 0);
bot = top;
for (int i = 0; i <= countVisibleLines; i++) {
iLine = iTopLine + i;
if (iLine >= tb.LinesCount) break;
line = tb.GetRealLine(iLine);
if (!line.Unavaliable) bot = line.LineNo - 1;
}
bot++;
}