fix dagre shifting connection start past 2nd point

d2graph/layout.go

@@ -141,6 +141,118 @@ func (obj *Object) ShiftDescendants(dx, dy float64) {
 	})
 }
 
+// ShiftStart moves the starting point of the route by delta either horizontally or vertically
+// if subsequent points are in line with the movement, they will be removed (unless it is the last point)
+// start                   end
+// . ├────┼────┼───┼────┼───┤   before
+// . ├──dx──►
+// .        ├──┼───┼────┼───┤   after
+func (edge *Edge) ShiftStart(delta float64, isHorizontal bool) {
+	position := func(p *geo.Point) float64 {
+		if isHorizontal {
+			return p.X
+		}
+		return p.Y
+	}
+
+	start := edge.Route[0]
+	next := edge.Route[1]
+	isIncreasing := position(start) < position(next)
+	if isHorizontal {
+		start.X += delta
+	} else {
+		start.Y += delta
+	}
+
+	if isIncreasing == (delta < 0) {
+		// nothing more to do when moving away from the next point
+		return
+	}
+
+	isAligned := func(p *geo.Point) bool {
+		if isHorizontal {
+			return p.Y == start.Y
+		}
+		return p.X == start.X
+	}
+	isPastStart := func(p *geo.Point) bool {
+		if delta > 0 {
+			return position(p) < position(start)
+		} else {
+			return position(p) > position(start)
+		}
+	}
+
+	needsRemoval := false
+	toRemove := make([]bool, len(edge.Route))
+	for i := 1; i < len(edge.Route)-1; i++ {
+		if !isAligned(edge.Route[i]) {
+			break
+		}
+		if isPastStart(edge.Route[i]) {
+			toRemove[i] = true
+			needsRemoval = true
+		}
+	}
+	if needsRemoval {
+		edge.Route = geo.RemovePoints(edge.Route, toRemove)
+	}
+}
+
+// ShiftEnd moves the ending point of the route by delta either horizontally or vertically
+// if prior points are in line with the movement, they will be removed (unless it is the first point)
+func (edge *Edge) ShiftEnd(delta float64, isHorizontal bool) {
+	position := func(p *geo.Point) float64 {
+		if isHorizontal {
+			return p.X
+		}
+		return p.Y
+	}
+
+	end := edge.Route[len(edge.Route)-1]
+	prev := edge.Route[len(edge.Route)-2]
+	isIncreasing := position(prev) < position(end)
+	if isHorizontal {
+		end.X += delta
+	} else {
+		end.Y += delta
+	}
+
+	if isIncreasing == (delta > 0) {
+		// nothing more to do when moving away from the next point
+		return
+	}
+
+	isAligned := func(p *geo.Point) bool {
+		if isHorizontal {
+			return p.Y == end.Y
+		}
+		return p.X == end.X
+	}
+	isPastEnd := func(p *geo.Point) bool {
+		if delta > 0 {
+			return position(p) < position(end)
+		} else {
+			return position(p) > position(end)
+		}
+	}
+
+	needsRemoval := false
+	toRemove := make([]bool, len(edge.Route))
+	for i := len(edge.Route) - 2; i > 0; i-- {
+		if !isAligned(edge.Route[i]) {
+			break
+		}
+		if isPastEnd(edge.Route[i]) {
+			toRemove[i] = true
+			needsRemoval = true
+		}
+	}
+	if needsRemoval {
+		edge.Route = geo.RemovePoints(edge.Route, toRemove)
+	}
+}
+
 // GetModifierElementAdjustments returns width/height adjustments to account for shapes with 3d or multiple
 func (obj *Object) GetModifierElementAdjustments() (dx, dy float64) {
 	if obj.Is3D() {

d2layouts/d2dagrelayout/layout.go

@@ -384,7 +384,7 @@ func Layout(ctx context.Context, g *d2graph.Graph, opts *ConfigurableOpts) (err
 						if isHorizontal && e.Src.Parent != g.Root && e.Dst.Parent != g.Root {
 							moveWholeEdge = true
 						} else {
-							e.Route[0].Y += stepSize
+							e.ShiftStart(stepSize, false)
 						}
 					}
 				}
@@ -393,7 +393,7 @@ func Layout(ctx context.Context, g *d2graph.Graph, opts *ConfigurableOpts) (err
 						if isHorizontal && e.Dst.Parent != g.Root && e.Src.Parent != g.Root {
 							moveWholeEdge = true
 						} else {
-							e.Route[len(e.Route)-1].Y += stepSize
+							e.ShiftEnd(stepSize, false)
 						}
 					}
 				}

lib/geo/point.go

@@ -305,3 +305,22 @@ func (p *Point) TruncateDecimals() {
 	p.X = TruncateDecimals(p.X)
 	p.Y = TruncateDecimals(p.Y)
 }
+
+// RemovePoints returns a new Points slice without the points in toRemove
+func RemovePoints(points Points, toRemove []bool) Points {
+	newLen := len(points)
+	for _, should := range toRemove {
+		if should {
+			newLen--
+		}
+	}
+
+	without := make([]*Point, 0, newLen)
+	for i := 0; i < len(points); i++ {
+		if toRemove[i] {
+			continue
+		}
+		without = append(without, points[i])
+	}
+	return without
+}