Adds basic sequence diagrams behind a layout flag

d2layouts/d2sequence/constants.go

@@ -0,0 +1,9 @@
+package d2sequence
+
+// min horizontal pad for actors, or edge labels, to consider the min distance between them
+const MIN_HORIZONTAL_PAD = 50.
+
+const MIN_ACTOR_DISTANCE = 200.
+
+// min vertical distance between edges
+const MIN_EDGE_DISTANCE = 100.

d2layouts/d2sequence/layout.go

@@ -12,45 +12,33 @@ import (
 )
 
 func Layout(ctx context.Context, g *d2graph.Graph) (err error) {
-	pad := 50. // 2 * 25
-	edgeYStep := 100.
-	objectXStep := 200.
-	maxObjectHeight := 0.
+	pad := MIN_HORIZONTAL_PAD
+	edgeYStep := MIN_EDGE_DISTANCE
+	actorXStep := MIN_ACTOR_DISTANCE
+	maxActorHeight := 0.
 
-	var objectsInOrder []*d2graph.Object
-	seen := make(map[*d2graph.Object]struct{})
 	for _, edge := range g.Edges {
-		if _, exists := seen[edge.Src]; !exists {
-			seen[edge.Src] = struct{}{}
-			objectsInOrder = append(objectsInOrder, edge.Src)
-		}
-		if _, exists := seen[edge.Dst]; !exists {
-			seen[edge.Dst] = struct{}{}
-			objectsInOrder = append(objectsInOrder, edge.Dst)
-		}
-
 		edgeYStep = math.Max(edgeYStep, float64(edge.LabelDimensions.Height)+pad)
-		objectXStep = math.Max(objectXStep, float64(edge.LabelDimensions.Width)+pad)
-		maxObjectHeight = math.Max(maxObjectHeight, edge.Src.Height+pad)
-		maxObjectHeight = math.Max(maxObjectHeight, edge.Dst.Height+pad)
+		actorXStep = math.Max(actorXStep, float64(edge.LabelDimensions.Width)+pad)
+		maxActorHeight = math.Max(maxActorHeight, edge.Src.Height+pad)
+		maxActorHeight = math.Max(maxActorHeight, edge.Dst.Height+pad)
 	}
 
-	placeObjects(objectsInOrder, maxObjectHeight, objectXStep)
-	// edges are placed in the order users define them
-	routeEdges(g.Edges, maxObjectHeight, edgeYStep)
-	addLifelineEdges(g, objectsInOrder, edgeYStep)
+	placeActors(g.Objects, maxActorHeight, actorXStep)
+	routeEdges(g.Edges, maxActorHeight, edgeYStep)
+	addLifelineEdges(g, g.Objects, edgeYStep)
 
 	return nil
 }
 
-// placeObjects places objects side by side
-func placeObjects(objectsInOrder []*d2graph.Object, maxHeight, xStep float64) {
+// placeActors places actors bottom aligned, side by side
+func placeActors(actors []*d2graph.Object, maxHeight, xStep float64) {
 	x := 0.
-	for _, obj := range objectsInOrder {
-		yDiff := maxHeight - obj.Height
-		obj.TopLeft = geo.NewPoint(x, yDiff/2.)
-		x += obj.Width + xStep
-		obj.LabelPosition = go2.Pointer(string(label.InsideMiddleCenter))
+	for _, actors := range actors {
+		yOffset := maxHeight - actors.Height
+		actors.TopLeft = geo.NewPoint(x, yOffset)
+		x += actors.Width + xStep
+		actors.LabelPosition = go2.Pointer(string(label.InsideMiddleCenter))
 	}
 }
 
@@ -66,45 +54,47 @@ func routeEdges(edgesInOrder []*d2graph.Edge, startY, yStep float64) {
 		edgeY += yStep
 
 		if edge.Attributes.Label.Value != "" {
-			// TODO: consider label right-to-left
-			edge.LabelPosition = go2.Pointer(string(label.OutsideTopCenter))
+			isLeftToRight := edge.Src.TopLeft.X < edge.Dst.TopLeft.X
+			if isLeftToRight {
+				edge.LabelPosition = go2.Pointer(string(label.OutsideTopCenter))
+			} else {
+				edge.LabelPosition = go2.Pointer(string(label.OutsideBottomCenter))
+			}
 		}
 	}
 }
 
-// addLifelineEdges adds a new edge for each object in the graph that represents the
-// edge below he object showing its lifespan
+// addLifelineEdges adds a new edge for each actor in the graph that represents the
+// edge below the actor showing its lifespan
 // ┌──────────────┐
-// │    object    │
+// │     actor    │
 // └──────┬───────┘
 //        │
 //        │ lifeline
 //        │
 //        │
-func addLifelineEdges(g *d2graph.Graph, objectsInOrder []*d2graph.Object, yStep float64) {
+func addLifelineEdges(g *d2graph.Graph, actors []*d2graph.Object, yStep float64) {
 	endY := g.Edges[len(g.Edges)-1].Route[0].Y + yStep
-	for _, obj := range objectsInOrder {
-		objBottom := obj.Center()
-		objBottom.Y = obj.TopLeft.Y + obj.Height
-		objLifelineEnd := obj.Center()
-		objLifelineEnd.Y = endY
+	for _, actor := range actors {
+		actorBottom := actor.Center()
+		actorBottom.Y = actor.TopLeft.Y + actor.Height
+		actorLifelineEnd := actor.Center()
+		actorLifelineEnd.Y = endY
 		g.Edges = append(g.Edges, &d2graph.Edge{
 			Attributes: d2graph.Attributes{
 				Style: d2graph.Style{
-					StrokeDash: &d2graph.Scalar{
-						Value: "10",
-					},
-					Stroke:      obj.Attributes.Style.Stroke,
-					StrokeWidth: obj.Attributes.Style.StrokeWidth,
+					StrokeDash:  &d2graph.Scalar{Value: "10"},
+					Stroke:      actor.Attributes.Style.Stroke,
+					StrokeWidth: actor.Attributes.Style.StrokeWidth,
 				},
 			},
-			Src:      obj,
+			Src:      actor,
 			SrcArrow: false,
 			Dst: &d2graph.Object{
-				ID: obj.ID + fmt.Sprintf("-lifeline-end-%d", go2.StringToIntHash(obj.ID+"-lifeline-end")),
+				ID: actor.ID + fmt.Sprintf("-lifeline-end-%d", go2.StringToIntHash(actor.ID+"-lifeline-end")),
 			},
 			DstArrow: false,
-			Route:    []*geo.Point{objBottom, objLifelineEnd},
+			Route:    []*geo.Point{actorBottom, actorLifelineEnd},
 		})
 	}
 }

d2layouts/d2sequence/layout_test.go

@@ -45,27 +45,29 @@ func TestLayout(t *testing.T) {
 	ctx := log.WithTB(context.Background(), t, nil)
 	Layout(ctx, g)
 
-	// asserts that objects were placed in the expected x order and at y=0
-	objectsOrder := []*d2graph.Object{
+	// asserts that actors were placed in the expected x order and at y=0
+	actors := []*d2graph.Object{
 		g.Objects[0],
 		g.Objects[1],
 	}
-	for i := 1; i < len(objectsOrder); i++ {
-		if objectsOrder[i].TopLeft.X < objectsOrder[i-1].TopLeft.X {
-			t.Fatalf("expected object[%d].TopLeft.X > object[%d].TopLeft.X", i, i-1)
+	for i := 1; i < len(actors); i++ {
+		if actors[i].TopLeft.X < actors[i-1].TopLeft.X {
+			t.Fatalf("expected actor[%d].TopLeft.X > actor[%d].TopLeft.X", i, i-1)
 		}
-		if objectsOrder[i].Center().Y != objectsOrder[i-1].Center().Y {
-			t.Fatalf("expected object[%d] and object[%d] to be at the same center y", i, i-1)
+		actorBottom := actors[i].TopLeft.Y + actors[i].Height
+		prevActorBottom := actors[i-1].TopLeft.Y + actors[i-1].Height
+		if actorBottom != prevActorBottom {
+			t.Fatalf("expected actor[%d] and actor[%d] to be at the same bottom y", i, i-1)
 		}
 	}
 
-	nExpectedEdges := nEdges + len(objectsOrder)
+	nExpectedEdges := nEdges + len(actors)
 	if len(g.Edges) != nExpectedEdges {
 		t.Fatalf("expected %d edges, got %d", nExpectedEdges, len(g.Edges))
 	}
 
-	// assert that edges were placed in y order and have the endpoints at their objects
-	// uses `nEdges` because Layout creates some vertical edges to represent the object lifeline
+	// assert that edges were placed in y order and have the endpoints at their actors
+	// uses `nEdges` because Layout creates some vertical edges to represent the actor lifeline
 	for i := 0; i < nEdges; i++ {
 		edge := g.Edges[i]
 		if len(edge.Route) != 2 {
@@ -75,10 +77,10 @@ func TestLayout(t *testing.T) {
 			t.Fatalf("expected edge[%d] to be a horizontal line", i)
 		}
 		if edge.Route[0].X != edge.Src.Center().X {
-			t.Fatalf("expected edge[%d] source endpoint to be at the middle of the source object", i)
+			t.Fatalf("expected edge[%d] source endpoint to be at the middle of the source actor", i)
 		}
 		if edge.Route[1].X != edge.Dst.Center().X {
-			t.Fatalf("expected edge[%d] target endpoint to be at the middle of the target object", i)
+			t.Fatalf("expected edge[%d] target endpoint to be at the middle of the target actor", i)
 		}
 		if i > 0 {
 			prevEdge := g.Edges[i-1]
@@ -98,10 +100,10 @@ func TestLayout(t *testing.T) {
 			t.Fatalf("expected edge[%d] to be a vertical line", i)
 		}
 		if edge.Route[0].X != edge.Src.Center().X {
-			t.Fatalf("expected edge[%d] x to be at the object center", i)
+			t.Fatalf("expected edge[%d] x to be at the actor center", i)
 		}
 		if edge.Route[0].Y != edge.Src.Height+edge.Src.TopLeft.Y {
-			t.Fatalf("expected edge[%d] to start at the bottom of the source object", i)
+			t.Fatalf("expected edge[%d] to start at the bottom of the source actor", i)
 		}
 		if edge.Route[1].Y < lastSequenceEdge.Route[0].Y {
 			t.Fatalf("expected edge[%d] to end after the last sequence edge", i)