Self review.

draw/hv_line.go

@@ -49,8 +49,6 @@ func HVLineStyle(ls LineStyle) HVLineOption {
 }
 
 // HVLineCellOpts sets options on the cells that contain the line.
-// Where two lines cross, the cell representing the crossing point inherits
-// options set on the line that was drawn last.
 func HVLineCellOpts(cOpts ...cell.Option) HVLineOption {
 	return hVLineOption(func(opts *hVLineOptions) {
 		opts.cellOpts = cOpts
@@ -65,7 +63,7 @@ type HVLine struct {
 
 // HVLines draws horizontal or vertical lines. Handles drawing of the correct
 // characters for locations where any two lines cross (e.g. a corner, a T shape
-// a cross). Each line must be at least one cell long. Both start and end
+// or a cross). Each line must be at least one cell long. Both start and end
 // must be on the same horizontal (same X coordinate) or same vertical (same Y
 // coordinate) line.
 func HVLines(c *canvas.Canvas, lines []HVLine, opts ...HVLineOption) error {
@@ -130,10 +128,6 @@ type hVLine struct {
 	// end is the ending point of the line.
 	end image.Point
 
-	// parts are characters that represent parts of the line of the style
-	// chosen in the options.
-	parts map[linePart]rune
-
 	// mainPart is either parts[vLine] or parts[hLine] depending on whether
 	// this is horizontal or vertical line.
 	mainPart rune
@@ -143,7 +137,7 @@ type hVLine struct {
 }
 
 // newHVLine creates a new hVLine instance.
-// Swaps start and end iof necessary, so that horizontal drawing is always left
+// Swaps start and end if necessary, so that horizontal drawing is always left
 // to right and vertical is always top down.
 func newHVLine(c *canvas.Canvas, start, end image.Point, opts *hVLineOptions) (*hVLine, error) {
 	if ar := c.Area(); !start.In(ar) || !end.In(ar) {
@@ -180,7 +174,6 @@ func newHVLine(c *canvas.Canvas, start, end image.Point, opts *hVLineOptions) (*
 	return &hVLine{
 		start:    start,
 		end:      end,
-		parts:    parts,
 		mainPart: mainPart,
 		opts:     opts,
 	}, nil
@@ -188,10 +181,10 @@ func newHVLine(c *canvas.Canvas, start, end image.Point, opts *hVLineOptions) (*
 
 // horizontal determines if this is a horizontal line.
 func (hvl *hVLine) horizontal() bool {
-	return hvl.mainPart == hvl.parts[hLine]
+	return hvl.mainPart == lineStyleChars[hvl.opts.lineStyle][hLine]
 }
 
 // vertical determines if this is a vertical line.
 func (hvl *hVLine) vertical() bool {
-	return hvl.mainPart == hvl.parts[vLine]
+	return hvl.mainPart == lineStyleChars[hvl.opts.lineStyle][vLine]
 }

draw/hv_line_graph.go

@@ -23,8 +23,12 @@ import (
 
 // hVLineEdge is an edge between two points on the graph.
 type hVLineEdge struct {
+	// from is the starting node of this edge.
+	// From is guaranteed to be less than to.
 	from image.Point
-	to   image.Point
+
+	// to is the ending point of this edge.
+	to image.Point
 }
 
 // newHVLineEdge returns a new edge between the two points.
@@ -41,7 +45,9 @@ type hVLineNode struct {
 	// p is the point where this node is.
 	p image.Point
 
-	// edges are the edges from this node to the neighboring nodes.
+	// edges are the edges between this node and the surrounding nodes.
+	// The code only supports horizontal and vertical lines so there can only
+	// ever be edges to nodes on these planes.
 	edges map[hVLineEdge]bool
 }
 
@@ -83,22 +89,28 @@ func (n *hVLineNode) hasRight() bool {
 
 // rune, given the selected line style returns the correct line character to
 // represent this node.
+// Only handles nodes with two or more edges, as returned by multiEdgeNodes().
 func (n *hVLineNode) rune(ls LineStyle) (rune, error) {
+	parts, err := lineParts(ls)
+	if err != nil {
+		return -1, err
+	}
+
 	switch len(n.edges) {
 	case 2:
 		switch {
 		case n.hasLeft() && n.hasRight():
-			return lineStyleChars[ls][hLine], nil
+			return parts[hLine], nil
 		case n.hasUp() && n.hasDown():
-			return lineStyleChars[ls][vLine], nil
+			return parts[vLine], nil
 		case n.hasDown() && n.hasRight():
-			return lineStyleChars[ls][topLeftCorner], nil
+			return parts[topLeftCorner], nil
 		case n.hasDown() && n.hasLeft():
-			return lineStyleChars[ls][topRightCorner], nil
+			return parts[topRightCorner], nil
 		case n.hasUp() && n.hasRight():
-			return lineStyleChars[ls][bottomLeftCorner], nil
+			return parts[bottomLeftCorner], nil
 		case n.hasUp() && n.hasLeft():
-			return lineStyleChars[ls][bottomRightCorner], nil
+			return parts[bottomRightCorner], nil
 		default:
 			return -1, fmt.Errorf("unexpected two edges in node representing point %v: %v", n.p, n.edges)
 		}
@@ -106,20 +118,20 @@ func (n *hVLineNode) rune(ls LineStyle) (rune, error) {
 	case 3:
 		switch {
 		case n.hasUp() && n.hasLeft() && n.hasRight():
-			return lineStyleChars[ls][hAndUp], nil
+			return parts[hAndUp], nil
 		case n.hasDown() && n.hasLeft() && n.hasRight():
-			return lineStyleChars[ls][hAndDown], nil
+			return parts[hAndDown], nil
 		case n.hasUp() && n.hasDown() && n.hasRight():
-			return lineStyleChars[ls][vAndRight], nil
+			return parts[vAndRight], nil
 		case n.hasUp() && n.hasDown() && n.hasLeft():
-			return lineStyleChars[ls][vAndLeft], nil
+			return parts[vAndLeft], nil
 
 		default:
 			return -1, fmt.Errorf("unexpected three edges in node representing point %v: %v", n.p, n.edges)
 		}
 
 	case 4:
-		return lineStyleChars[ls][vAndH], nil
+		return parts[vAndH], nil
 	default:
 		return -1, fmt.Errorf("unexpected number of edges(%d) in node representing point %v", len(n.edges), n.p)
 	}

draw/hv_line_graph_test.go

@@ -212,6 +212,12 @@ func TestNodeRune(t *testing.T) {
 			ls:      LineStyleLight,
 			wantErr: true,
 		},
+		{
+			desc:    "fails on unsupported line style",
+			node:    &hVLineNode{},
+			ls:      LineStyle(-1),
+			wantErr: true,
+		},
 		{
 			desc: "horizontal line",
 			node: &hVLineNode{

draw/line_style.go

@@ -53,13 +53,11 @@ func init() {
 	}
 }
 
-// TODO(mum4k): Check inside init() that all of these are half-width runes.
-
 // lineParts returns the line component characters for the provided line style.
 func lineParts(ls LineStyle) (map[linePart]rune, error) {
 	parts, ok := lineStyleChars[ls]
 	if !ok {
-		return nil, fmt.Errorf("unsupported line style %v", ls)
+		return nil, fmt.Errorf("unsupported line style %d", ls)
 	}
 	return parts, nil
 }