plot: Make Align honor tile margins

align.go

@@ -63,12 +63,12 @@ func Align(plots [][]*Plot, t draw.Tiles, dc draw.Canvas) [][]draw.Canvas {
 	for _, s := range xSpacing {
 		xTotalSpace += s.n + s.p
 	}
-	xTotalSpace += float64(t.PadX) * float64(len(xSpacing)-1)
+	xTotalSpace += float64(t.PadX)*float64(len(xSpacing)-1) + float64(t.PadLeft+t.PadRight)
 	var yTotalSpace float64
 	for _, s := range ySpacing {
 		yTotalSpace += s.n + s.p
 	}
-	yTotalSpace += float64(t.PadY) * float64(len(ySpacing)-1)
+	yTotalSpace += float64(t.PadY)*float64(len(ySpacing)-1) + float64(t.PadTop+t.PadBottom)
 
 	avgWidth := vg.Length((float64(dc.Max.X-dc.Min.X) - xTotalSpace) / float64(t.Cols))
 	avgHeight := vg.Length((float64(dc.Max.Y-dc.Min.Y) - yTotalSpace) / float64(t.Rows))

align_test.go

@@ -62,10 +62,14 @@ func ExampleAlign() {
 	dc := draw.New(img)
 
 	t := draw.Tiles{
-		Rows: rows,
-		Cols: cols,
-		PadX: vg.Millimeter,
-		PadY: vg.Millimeter,
+		Rows:      rows,
+		Cols:      cols,
+		PadX:      vg.Millimeter,
+		PadY:      vg.Millimeter,
+		PadTop:    vg.Points(2),
+		PadBottom: vg.Points(2),
+		PadLeft:   vg.Points(2),
+		PadRight:  vg.Points(2),
 	}
 
 	canvases := Align(plots, t, dc)