ProgressBar: with progress-bar-width, center marker on current position.

Previously, the bar's leading (right) edge sat at the current video
position, mainly because I hadn't realized how easy this would be to
implement. This change will probably look odd with large values of
progress-bar-width; however, that isn't the intended use case, and this
change looks significantly better at small values (say, between 0 and
10).

src/ProgressBar.moon

@@ -3,26 +3,33 @@ class ProgressBar extends BarBase
 	seekString = ('absolute-percent+%s')\format settings['seek-precision']
 
 	new: =>
+		-- super calls reconfigure which sets barShift.
 		super!
 		@lastPosition = 0
 
 	reconfigure: =>
 		super!
 		seekString = ('absolute-percent+%s')\format settings['seek-precision']
-		@barWidth = settings['progress-bar-width']
+		@barShift = settings['progress-bar-width']/2.0
+		@resize!
 		@line[7] = [[]]
 		@line[8] = @line[8]\format settings['bar-foreground-style']
 
 	clickHandler: =>
 		mp.commandv "seek", Mouse.clickX*100/Window.w, seekString
 
+	resize: =>
+		super!
+		if @barShift > 0
+			@line[2] = ('%g,%g')\format @barShift, Window.h
+
 	redraw: =>
 		super!
 		position = mp.get_property_number 'percent-pos', 0
 		if position != @lastPosition or @needsUpdate
 			@line[6] = position
-			if @barWidth > 0
-				followingEdge = Window.w*position*1e-2 - @barWidth
+			if @barShift > 0
+				followingEdge = Window.w*position*1e-2 - @barShift
 				@line[7] = [[\clip(m %g 0 l %g 0 %g %g %g %g)]]\format followingEdge, Window.w, Window.w, Window.h, followingEdge, Window.h
 			@lastPosition = position
 			@needsUpdate = true