I want to draw some round-ended rectangles to use as labels, so I thought a filled arc either end would work (silly me :-)
\draw [fill](0,0) arc[radius=5pt,start angle= 90,end angle=270]; \draw [fill](0,0) rectangle (40,-20); \draw [fill](40,0) arc[radius=5pt,start angle=270,end angle=90];
But this places the right-hand end-cap above the rectangle, and facing the wrong way. I have obviously misunderstood the implications of the direction angles.
How do I draw a filled arc that points right, not left? (that is, D-shaped, the mirror of the first one).