shape: cycle - trace arcs to shape borders (close #1578)

d2graph/cyclediagram.go

@@ -0,0 +1,7 @@
+package d2graph
+
+import "oss.terrastruct.com/d2/d2target"
+
+func (obj *Object) IsCycleDiagram() bool {
+	return obj != nil && obj.Shape.Value == d2target.ShapeCycleDiagram
+}

d2layouts/d2cycle/layout.go

@@ -0,0 +1,259 @@
+package d2cycle
+
+import (
+	"context"
+	"math"
+
+	"oss.terrastruct.com/d2/d2graph"
+	"oss.terrastruct.com/d2/lib/geo"
+	"oss.terrastruct.com/d2/lib/label"
+	"oss.terrastruct.com/d2/lib/shape"
+	"oss.terrastruct.com/util-go/go2"
+)
+
+const (
+	MIN_RADIUS = 200
+	PADDING    = 20
+	ARC_STEPS  = 30
+)
+
+// Layout arranges nodes in a circle and routes each edge as a circular arc
+// that starts and ends on the borders of its source and destination shapes.
+func Layout(ctx context.Context, g *d2graph.Graph, layout d2graph.LayoutGraph) error {
+	objects := g.Root.ChildrenArray
+	if len(objects) == 0 {
+		return nil
+	}
+
+	for _, obj := range g.Objects {
+		positionLabelsIcons(obj)
+	}
+
+	radius := calculateRadius(objects)
+	positionObjects(objects, radius)
+
+	for _, edge := range g.Edges {
+		createCircularArc(edge, radius)
+	}
+
+	return nil
+}
+
+func calculateRadius(objects []*d2graph.Object) float64 {
+	numObjects := float64(len(objects))
+	maxSize := 0.0
+	for _, obj := range objects {
+		size := math.Max(obj.Box.Width, obj.Box.Height)
+		maxSize = math.Max(maxSize, size)
+	}
+	minRadius := (maxSize/2.0 + PADDING) / math.Sin(math.Pi/numObjects)
+	return math.Max(minRadius, MIN_RADIUS)
+}
+
+func positionObjects(objects []*d2graph.Object, radius float64) {
+	numObjects := float64(len(objects))
+	angleOffset := -math.Pi / 2
+
+	for i, obj := range objects {
+		angle := angleOffset + (2 * math.Pi * float64(i) / numObjects)
+		x := radius * math.Cos(angle)
+		y := radius * math.Sin(angle)
+
+		obj.TopLeft = geo.NewPoint(
+			x-obj.Box.Width/2,
+			y-obj.Box.Height/2,
+		)
+	}
+}
+
+// createCircularArc routes a single edge as a circular arc whose endpoints
+// lie exactly on the borders of the source and destination shapes. The arc
+// belongs to the layout circle, centered at the origin with the given radius;
+// the source and destination shape centers both lie on that circle.
+func createCircularArc(edge *d2graph.Edge, radius float64) {
+	if edge.Src == nil || edge.Dst == nil {
+		return
+	}
+
+	srcCenter := edge.Src.Center()
+	dstCenter := edge.Dst.Center()
+	origin := geo.NewPoint(0, 0)
+
+	srcAngle := math.Atan2(srcCenter.Y, srcCenter.X)
+	dstAngle := math.Atan2(dstCenter.Y, dstCenter.X)
+	if dstAngle < srcAngle {
+		dstAngle += 2 * math.Pi
+	}
+	sweep := dstAngle - srcAngle
+	srcShape := edge.Src.ToShape()
+	dstShape := edge.Dst.ToShape()
+	if sweep <= 0 {
+		fallbackStraightRoute(edge, srcShape, dstShape, srcCenter, dstCenter)
+		return
+	}
+
+	startAngle, hasStart := nextBoundaryAngle(edge.Src.Box, origin, radius, srcAngle, sweep, true)
+	endAngle, hasEnd := nextBoundaryAngle(edge.Dst.Box, origin, radius, srcAngle, sweep, false)
+	if !hasStart || !hasEnd || endAngle <= startAngle {
+		fallbackStraightRoute(edge, srcShape, dstShape, srcCenter, dstCenter)
+		return
+	}
+
+	path := make([]*geo.Point, 0, ARC_STEPS+1)
+	for i := 0; i <= ARC_STEPS; i++ {
+		t := float64(i) / float64(ARC_STEPS)
+		angle := startAngle + t*(endAngle-startAngle)
+		path = append(path, geo.NewPoint(radius*math.Cos(angle), radius*math.Sin(angle)))
+	}
+
+	// path[0] / path[len-1] sit on the bounding-box border of the source /
+	// destination shape. For non-rectangular shapes (circle, oval, hexagon,
+	// cloud, ...) the bounding box border is not the shape border, so trace
+	// each endpoint inward from the shape center to the actual shape outline.
+	// TraceToShapeBorder is a no-op for rectangular shapes.
+	path[0] = shape.TraceToShapeBorder(srcShape, path[0], srcCenter)
+	path[len(path)-1] = shape.TraceToShapeBorder(dstShape, path[len(path)-1], dstCenter)
+
+	edge.Route = path
+	edge.IsCurve = true
+}
+
+// fallbackStraightRoute renders a straight connection whose endpoints are
+// clipped to the source and destination shape borders along the line between
+// the two centers, used when the analytic arc geometry degenerates (zero
+// sweep, no boundary crossing in the arc range, etc.).
+func fallbackStraightRoute(edge *d2graph.Edge, srcShape, dstShape shape.Shape, srcCenter, dstCenter *geo.Point) {
+	srcBorder := clipToShapeBorder(srcShape, edge.Src.Box, srcCenter, dstCenter)
+	dstBorder := clipToShapeBorder(dstShape, edge.Dst.Box, dstCenter, srcCenter)
+	edge.Route = []*geo.Point{srcBorder, dstBorder}
+	edge.IsCurve = false
+}
+
+// clipToShapeBorder returns the point where a ray from `from` (assumed inside
+// `box`) toward `toward` first exits the actual shape outline. The bounding
+// box is consulted first to obtain a rectangular border point, then the shape
+// helper refines it for non-rectangular shapes.
+func clipToShapeBorder(shp shape.Shape, box *geo.Box, from, toward *geo.Point) *geo.Point {
+	dx := toward.X - from.X
+	dy := toward.Y - from.Y
+	dist := math.Hypot(dx, dy)
+	if dist == 0 {
+		return from
+	}
+	// Extend the ray well past `toward` so the segment definitely exits the
+	// box even when `toward` itself sits inside the box.
+	diag := math.Hypot(box.Width, box.Height)
+	scale := (dist + 2*diag) / dist
+	extended := geo.NewPoint(from.X+dx*scale, from.Y+dy*scale)
+
+	rectBorder := extended
+	if pts := box.Intersections(geo.Segment{Start: from, End: extended}); len(pts) > 0 {
+		rectBorder = pts[0]
+	}
+	return shape.TraceToShapeBorder(shp, rectBorder, from)
+}
+
+// nextBoundaryAngle scans the angles where the layout circle crosses an edge
+// of the box. When forSrc is true it returns the smallest such angle strictly
+// greater than srcAngle (the point where the arc exits the source box). When
+// forSrc is false it returns the largest such angle strictly less than
+// srcAngle+sweep (the point where the arc enters the destination box). The
+// boolean is false when no crossing exists in the (srcAngle, srcAngle+sweep)
+// range, in which case the caller falls back to the shape center.
+func nextBoundaryAngle(box *geo.Box, origin *geo.Point, radius, srcAngle, sweep float64, forSrc bool) (float64, bool) {
+	candidates := boxCircleIntersectionAngles(box, origin, radius)
+	endAngle := srcAngle + sweep
+
+	var best float64
+	found := false
+	for _, raw := range candidates {
+		a := raw
+		for a <= srcAngle {
+			a += 2 * math.Pi
+		}
+		for a > srcAngle+2*math.Pi {
+			a -= 2 * math.Pi
+		}
+		if a >= endAngle {
+			continue
+		}
+		if !found {
+			best = a
+			found = true
+			continue
+		}
+		if forSrc {
+			if a < best {
+				best = a
+			}
+		} else {
+			if a > best {
+				best = a
+			}
+		}
+	}
+	return best, found
+}
+
+func boxCircleIntersectionAngles(box *geo.Box, origin *geo.Point, radius float64) []float64 {
+	edges := boxEdges(box)
+	var angles []float64
+	for _, e := range edges {
+		for _, p := range e.IntersectCircle(origin, radius) {
+			angles = append(angles, math.Atan2(p.Y-origin.Y, p.X-origin.X))
+		}
+	}
+	return angles
+}
+
+func boxEdges(box *geo.Box) []geo.Segment {
+	tl := box.TopLeft
+	tr := geo.NewPoint(tl.X+box.Width, tl.Y)
+	bl := geo.NewPoint(tl.X, tl.Y+box.Height)
+	br := geo.NewPoint(tl.X+box.Width, tl.Y+box.Height)
+	return []geo.Segment{
+		{Start: tl, End: tr},
+		{Start: tr, End: br},
+		{Start: br, End: bl},
+		{Start: bl, End: tl},
+	}
+}
+
+// positionLabelsIcons applies a sensible default label/icon position when one
+// has not been explicitly specified.
+func positionLabelsIcons(obj *d2graph.Object) {
+	if obj.Icon != nil && obj.IconPosition == nil {
+		if len(obj.ChildrenArray) > 0 {
+			obj.IconPosition = go2.Pointer(label.OutsideTopLeft.String())
+			if obj.LabelPosition == nil {
+				obj.LabelPosition = go2.Pointer(label.OutsideTopRight.String())
+				return
+			}
+		} else if obj.SQLTable != nil || obj.Class != nil || obj.Language != "" {
+			obj.IconPosition = go2.Pointer(label.OutsideTopLeft.String())
+		} else {
+			obj.IconPosition = go2.Pointer(label.InsideMiddleCenter.String())
+		}
+	}
+
+	if obj.HasLabel() && obj.LabelPosition == nil {
+		if len(obj.ChildrenArray) > 0 {
+			obj.LabelPosition = go2.Pointer(label.OutsideTopCenter.String())
+		} else if obj.HasOutsideBottomLabel() {
+			obj.LabelPosition = go2.Pointer(label.OutsideBottomCenter.String())
+		} else if obj.Icon != nil {
+			obj.LabelPosition = go2.Pointer(label.InsideTopCenter.String())
+		} else {
+			obj.LabelPosition = go2.Pointer(label.InsideMiddleCenter.String())
+		}
+
+		if float64(obj.LabelDimensions.Width) > obj.Width ||
+			float64(obj.LabelDimensions.Height) > obj.Height {
+			if len(obj.ChildrenArray) > 0 {
+				obj.LabelPosition = go2.Pointer(label.OutsideTopCenter.String())
+			} else {
+				obj.LabelPosition = go2.Pointer(label.OutsideBottomCenter.String())
+			}
+		}
+	}
+}

d2layouts/d2layouts.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"oss.terrastruct.com/d2/d2graph"
+	"oss.terrastruct.com/d2/d2layouts/d2cycle"
 	"oss.terrastruct.com/d2/d2layouts/d2grid"
 	"oss.terrastruct.com/d2/d2layouts/d2near"
 	"oss.terrastruct.com/d2/d2layouts/d2sequence"
@@ -20,12 +21,12 @@ import (
 
 type DiagramType string
 
-// a grid diagram at a constant near is
 const (
 	DefaultGraphType  DiagramType = ""
 	ConstantNearGraph DiagramType = "constant-near"
 	GridDiagram       DiagramType = "grid-diagram"
 	SequenceDiagram   DiagramType = "sequence-diagram"
+	CycleDiagram      DiagramType = "cycle-diagram"
 )
 
 type GraphInfo struct {
@@ -260,6 +261,12 @@ func LayoutNested(ctx context.Context, g *d2graph.Graph, graphInfo GraphInfo, co
 			if err != nil {
 				return err
 			}
+		case CycleDiagram:
+			log.Debug(ctx, "layout sequence", slog.Any("rootlevel", g.RootLevel), slog.Any("shapes", g.PrintString()))
+			err = d2cycle.Layout(ctx, g, coreLayout)
+			if err != nil {
+				return err
+			}
 		default:
 			log.Debug(ctx, "default layout", slog.Any("rootlevel", g.RootLevel), slog.Any("shapes", g.PrintString()))
 			err := coreLayout(ctx, g)
@@ -360,6 +367,8 @@ func NestedGraphInfo(obj *d2graph.Object) (gi GraphInfo) {
 		gi.DiagramType = SequenceDiagram
 	} else if obj.IsGridDiagram() {
 		gi.DiagramType = GridDiagram
+	} else if obj.IsCycleDiagram() {
+		gi.DiagramType = CycleDiagram
 	}
 	return gi
 }