WPF - 3000 rectangles - render speed

set all rects to 0,0, then then translatetransform is always done relative to this position, otherwise you may get a problem to know which rect is where.

something like:
Canvas.SetLeft(rect, 0);
Canvas.SetRight(rect, 0);
TranslateTransform trans = rect.RenderTransform = new TranslateTransform();
trans.X = rc.Left;
trans.Y = rc.Top;

...
later on
....
trans.X = newX;
trans.Y = newY;