/// <summary>
/// Get the range of pdf in the viewport.
/// </summary>
/// <param name="firstIndex">The first pdf index in the viewport.</param>
/// <param name="lastIndex">The last pdf index in the viewport.</param>
void GetVisibleRange(out int firstIndex, out int lastIndex)
{
var currentPosition = Math.Floor(svPdfContainer.VerticalOffset);
var lastPosition = Math.Floor(svPdfContainer.VerticalOffset + svPdfContainer.ViewportHeight);
var pdfRanges = PdfPages.Select(page => new { start = page.Bound.VerticalOffset, end = page.Bound.VerticalOffset + page.Bound.Height * ZoomRate, index = page.Index });
try
{
firstIndex = pdfRanges.Where(para => currentPosition >= para.start && currentPosition <= para.end).FirstOrDefault().index;
lastIndex = pdfRanges.Where(para => lastPosition >= para.start && lastPosition <= para.end).FirstOrDefault().index;
}
catch (Exception) // when last page position is in viewport
{
firstIndex = pdfRanges.Where(para => currentPosition >= para.start && currentPosition <= para.end).FirstOrDefault().index;
lastIndex = pdfRanges.LastOrDefault().index;
}
}
