public void InvalidateRange(int a, int b)
{
if (a < 0)
{
a = 0;
}
if (b < 0)
{
b = 0;
}
if (a > b)
{
int t = b;
b = a;
a = t;
}
int lineTop = tv.DisplayLineFromPosition(a);
int lineDocBottom = panel.pdoc.pbuffer.LineFromPosition(b) + 1;
int lineBottom = tv.fs.DisplayFromDoc(lineDocBottom);
SRectangle rcInvalidate = new SRectangle();
rcInvalidate.left = 0;
rcInvalidate.right = 2000;
rcInvalidate.top = (lineTop - panel.ScrollPos()) * tv.lineHeight;
rcInvalidate.bottom = (lineBottom - panel.ScrollPos()) * tv.lineHeight;
// Allow for decorators that go 2 pixels beyond line.
rcInvalidate.top -= 2;
rcInvalidate.bottom += 2;
Invalidate(new Rectangle(rcInvalidate.left, rcInvalidate.top,
rcInvalidate.Width(), rcInvalidate.Height()));
}