A signal label: rounded plate, contrasting text, and a tail that points at
anchorY. All coordinates are bitmap px — the caller has already applied dpr.
up puts the tail on the top edge and the body below the anchor.
text may carry \n: the plate widens to the longest row and grows
downward-and-upward about its own centre, so it stays centred on cx and the
tail keeps meeting the anchor price.
A signal label: rounded plate, contrasting text, and a tail that points at
anchorY. All coordinates are bitmap px — the caller has already applied dpr.upputs the tail on the top edge and the body below the anchor.textmay carry\n: the plate widens to the longest row and grows downward-and-upward about its own centre, so it stays centred oncxand the tail keeps meeting the anchor price.