adjust label positioning for arrowhead

d2renderers/d2svg/d2svg.go

@@ -20,8 +20,6 @@ import (
 	"github.com/alecthomas/chroma/v2/lexers"
 	"github.com/alecthomas/chroma/v2/styles"
 
-	"oss.terrastruct.com/util-go/go2"
-
 	"oss.terrastruct.com/d2/d2graph"
 	"oss.terrastruct.com/d2/d2renderers/d2fonts"
 	"oss.terrastruct.com/d2/d2renderers/d2latex"
@@ -40,7 +38,6 @@ import (
 
 const (
 	DEFAULT_PADDING = 100
-	MIN_ARROWHEAD_STROKE_WIDTH = 2
 
 	appendixIconRadius = 16
 )
@@ -109,56 +106,13 @@ func arrowheadMarkerID(isTarget bool, connection d2target.Connection) string {
 	)))
 }
 
-func arrowheadDimensions(arrowhead d2target.Arrowhead, strokeWidth float64) (width, height float64) {
-	var baseWidth, baseHeight float64
-	var widthMultiplier, heightMultiplier float64
-	switch arrowhead {
-	case d2target.ArrowArrowhead:
-		baseWidth = 4
-		baseHeight = 4
-		widthMultiplier = 4
-		heightMultiplier = 4
-	case d2target.TriangleArrowhead:
-		baseWidth = 4
-		baseHeight = 4
-		widthMultiplier = 3
-		heightMultiplier = 4
-	case d2target.LineArrowhead:
-		widthMultiplier = 5
-		heightMultiplier = 8
-	case d2target.FilledDiamondArrowhead:
-		baseWidth = 11
-		baseHeight = 7
-		widthMultiplier = 5.5
-		heightMultiplier = 3.5
-	case d2target.DiamondArrowhead:
-		baseWidth = 11
-		baseHeight = 9
-		widthMultiplier = 5.5
-		heightMultiplier = 4.5
-	case d2target.FilledCircleArrowhead, d2target.CircleArrowhead:
-		baseWidth = 8
-		baseHeight = 8
-		widthMultiplier = 5
-		heightMultiplier = 5
-	case d2target.CfOne, d2target.CfMany, d2target.CfOneRequired, d2target.CfManyRequired:
-		baseWidth = 9
-		baseHeight = 9
-		widthMultiplier = 4.5
-		heightMultiplier = 4.5
-	}
-
-	clippedStrokeWidth := go2.Max(MIN_ARROWHEAD_STROKE_WIDTH, strokeWidth)
-	return baseWidth + clippedStrokeWidth*widthMultiplier, baseHeight + clippedStrokeWidth*heightMultiplier
-}
-
 func arrowheadMarker(isTarget bool, id string, connection d2target.Connection) string {
 	arrowhead := connection.DstArrow
 	if !isTarget {
 		arrowhead = connection.SrcArrow
 	}
 	strokeWidth := float64(connection.StrokeWidth)
-	width, height := arrowheadDimensions(arrowhead, strokeWidth)
+	width, height := arrowhead.Dimensions(strokeWidth)
 
 	var path string
 	switch arrowhead {
@@ -621,11 +575,9 @@ func drawConnection(writer io.Writer, labelMaskID string, connection d2target.Co
 	}
 
 	if connection.SrcLabel != nil && connection.SrcLabel.Label != "" {
-		// TODO use arrowhead label dimensions https://github.com/terrastruct/d2/issues/183
 		fmt.Fprint(writer, renderArrowheadLabel(connection, connection.SrcLabel.Label, false))
 	}
 	if connection.DstLabel != nil && connection.DstLabel.Label != "" {
-		// TODO use arrowhead label dimensions https://github.com/terrastruct/d2/issues/183
 		fmt.Fprint(writer, renderArrowheadLabel(connection, connection.DstLabel.Label, true))
 	}
 	fmt.Fprintf(writer, `</g>`)
@@ -642,7 +594,7 @@ func renderArrowheadLabel(connection d2target.Connection, text string, isDst boo
 		height = float64(connection.SrcLabel.LabelHeight)
 	}
 
-	labelTL := connection.GetArrowHeadLabelPosition(isDst)
+	labelTL := connection.GetArrowheadLabelPosition(isDst)
 
 	// svg text is positioned with the center of its baseline
 	baselineCenter := geo.Point{

d2target/d2target.go

@@ -29,6 +29,9 @@ const (
 
 	BG_COLOR = color.N7
 	FG_COLOR = color.N1
+
+	MIN_ARROWHEAD_STROKE_WIDTH = 2
+	ARROWHEAD_PADDING          = 2.
 )
 
 var BorderOffset = geo.NewVector(5, 5)
@@ -233,14 +236,14 @@ func (diagram Diagram) BoundingBox() (topLeft, bottomRight Point) {
 			y2 = go2.Max(y2, int(labelTL.Y)+connection.LabelHeight)
 		}
 		if connection.SrcLabel != nil && connection.SrcLabel.Label != "" {
-			labelTL := connection.GetArrowHeadLabelPosition(false)
+			labelTL := connection.GetArrowheadLabelPosition(false)
 			x1 = go2.Min(x1, int(labelTL.X))
 			y1 = go2.Min(y1, int(labelTL.Y))
 			x2 = go2.Max(x2, int(labelTL.X)+connection.SrcLabel.LabelWidth)
 			y2 = go2.Max(y2, int(labelTL.Y)+connection.SrcLabel.LabelHeight)
 		}
 		if connection.DstLabel != nil && connection.DstLabel.Label != "" {
-			labelTL := connection.GetArrowHeadLabelPosition(true)
+			labelTL := connection.GetArrowheadLabelPosition(true)
 			x1 = go2.Min(x1, int(labelTL.X))
 			y1 = go2.Min(y1, int(labelTL.Y))
 			x2 = go2.Max(x2, int(labelTL.X)+connection.DstLabel.LabelWidth)
@@ -534,7 +537,7 @@ func (c *Connection) GetLabelTopLeft() *geo.Point {
 	return point
 }
 
-func (connection *Connection) GetArrowHeadLabelPosition(isDst bool) *geo.Point {
+func (connection *Connection) GetArrowheadLabelPosition(isDst bool) *geo.Point {
 	var width, height float64
 	if isDst {
 		width = float64(connection.DstLabel.LabelWidth)
@@ -578,36 +581,30 @@ func (connection *Connection) GetArrowHeadLabelPosition(isDst bool) *geo.Point {
 		}
 	}
 
-	labelTL, index := label.UnlockedTop.GetPointOnRoute(connection.Route, float64(connection.StrokeWidth), position, width, height)
+	strokeWidth := float64(connection.StrokeWidth)
 
-	var arrowheadOffset float64
+	labelTL, index := label.UnlockedTop.GetPointOnRoute(connection.Route, strokeWidth, position, width, height)
+
+	var arrowSize float64
 	if isDst && connection.DstArrow != NoArrowhead {
-		// TODO offset according to arrowhead dimensions
+		// Note: these dimensions are for rendering arrowheads on their side so we want the height
-		arrowheadOffset = 5
+		_, arrowSize = connection.DstArrow.Dimensions(strokeWidth)
 	} else if connection.SrcArrow != NoArrowhead {
-		arrowheadOffset = 5
+		_, arrowSize = connection.SrcArrow.Dimensions(strokeWidth)
 	}
 
-	var offsetX, offsetY float64
+	if arrowSize > 0 {
-	// get the start/end points of edge segment with arrowhead
+		// labelTL already accounts for strokeWidth and padding, we only want to shift further if the arrow is larger than this
+		offset := (arrowSize/2 + ARROWHEAD_PADDING) - strokeWidth/2 - label.PADDING
+		if offset > 0 {
 			start, end = connection.Route[index], connection.Route[index+1]
-	if start.Y == end.Y {
+			// Note: end to start to get normal towards unlocked top position
-		// shift up/down over horizontal segment
+			normalX, normalY := geo.GetUnitNormalVector(end.X, end.Y, start.X, start.Y)
-		offsetY = arrowheadOffset
+			labelTL.X += normalX * offset
-		if end.Y < start.Y {
+			labelTL.Y += normalY * offset
-			offsetY = -offsetY
-		}
-	} else if start.X == end.X {
-		// shift left/right across vertical segment
-		offsetX = arrowheadOffset
-		if end.X < start.X {
-			offsetX = -offsetX
 		}
 	}
 
-	labelTL.X += offsetX
-	labelTL.Y += offsetY
-
 	return labelTL
 }
 
@@ -681,6 +678,49 @@ func ToArrowhead(arrowheadType string, filled bool) Arrowhead {
 	}
 }
 
+func (arrowhead Arrowhead) Dimensions(strokeWidth float64) (width, height float64) {
+	var baseWidth, baseHeight float64
+	var widthMultiplier, heightMultiplier float64
+	switch arrowhead {
+	case ArrowArrowhead:
+		baseWidth = 4
+		baseHeight = 4
+		widthMultiplier = 4
+		heightMultiplier = 4
+	case TriangleArrowhead:
+		baseWidth = 4
+		baseHeight = 4
+		widthMultiplier = 3
+		heightMultiplier = 4
+	case LineArrowhead:
+		widthMultiplier = 5
+		heightMultiplier = 8
+	case FilledDiamondArrowhead:
+		baseWidth = 11
+		baseHeight = 7
+		widthMultiplier = 5.5
+		heightMultiplier = 3.5
+	case DiamondArrowhead:
+		baseWidth = 11
+		baseHeight = 9
+		widthMultiplier = 5.5
+		heightMultiplier = 4.5
+	case FilledCircleArrowhead, CircleArrowhead:
+		baseWidth = 8
+		baseHeight = 8
+		widthMultiplier = 5
+		heightMultiplier = 5
+	case CfOne, CfMany, CfOneRequired, CfManyRequired:
+		baseWidth = 9
+		baseHeight = 9
+		widthMultiplier = 4.5
+		heightMultiplier = 4.5
+	}
+
+	clippedStrokeWidth := go2.Max(MIN_ARROWHEAD_STROKE_WIDTH, strokeWidth)
+	return baseWidth + clippedStrokeWidth*widthMultiplier, baseHeight + clippedStrokeWidth*heightMultiplier
+}
+
 type Point struct {
 	X int `json:"x"`
 	Y int `json:"y"`