VS2010: Slow scrolling?

Question

I'm using the editor to scroll enough so that the line I want is at the top of the editor, to accomplish this i'm using

    private void performScroll(IHsEntries tag)
    {
      IViewScroller scroller = this._textView.ViewScroller;
      int start = tag.location.x1 + this._textView.TextBuffer.CurrentSnapshot.GetLineFromLineNumber(tag.location.y1).Start.Position;
      int length = tag.location.x2 - tag.location.x1;
      SnapshotSpan span = new SnapshotSpan(this._textView.TextBuffer.CurrentSnapshot, start, length);
      SnapshotSpan visibleSpan = this._textView.TextViewLines.FormattedSpan;
      int topline = this._textView.TextBuffer.CurrentSnapshot.GetLineFromPosition(visibleSpan.Start.Position).LineNumber;
      int needsScroll = tag.location.y1 - topline - 2;
      topline = needsScroll;
      needsScroll = Math.Max(Math.Abs(needsScroll), 0);

      scroller.ScrollViewportVerticallyByLines(topline > 0 ? ScrollDirection.Down : ScrollDirection.Up, needsScroll);
      //scroller.EnsureSpanVisible(span, EnsureSpanVisibleOptions.AlwaysCenter);
    }

which works, but has a very high noticable lag when it has to scroll a large distance. If I swap the last two lines, (so having it do the same number of calculations) the scroll is almost instantanously. So I'm wondering why it can center a scroll very quickly but not say scroll xxx lines down.

The larger the distance it has to scroll, the slower it is. I haven't had the time to upgrade to the RTM version yet so I'm still using the RC, but has anyone notice this same behaviour?

Answer 1

Hi Phyx - ScrollViewportVerticallyByLines will scroll one line at a time until all of the lines have been scrolled, which will cause layouts proportional to the number of lines.  EnsureSpanVisible does a single layout and is therefore significantly faster.  Make sense?

Brittany Behrens | Program Manager | Visual Studio Platform - Editor | The Visual Studio Blog | @VSEditor on Twitter

Answer 2

Hmm.. that's rather odd, I would have expected it to scroll the entire distance in one go. But ok, I can change how I calculate the visible span and then use one of the other methods which do scroll in one go.

Thanks :)