diff --git a/contour_layer.go b/contour_layer.go
index 1bd0ffb..a2b2ef0 100644
--- a/contour_layer.go
+++ b/contour_layer.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"fmt"
 	"math"
 	"math/rand"
 	"github.com/gen2brain/raylib-go/raylib"
@@ -8,21 +9,27 @@ import (
 
 type ContourLayer struct {
 	field  Field
+	maxActors uint32
 	actors []*Actor
+	actorIndex uint32
 	rng    *rand.Rand
 }
 
 func NewContourLayer(sketch *Sketch, rng *rand.Rand, field Field) *ContourLayer {
 
-	actors := make([]*Actor, 0)
+	maxActors := 200000
+
+	actors := make([]*Actor, maxActors)
 
 	layer := ContourLayer {
 		rng: rng,
 		field: field,
 		actors: actors,
+		maxActors: uint32(maxActors),
+		actorIndex: 0,
 	}
 
-	layer.AddActors(1, sketch.sourceWidth, sketch.sourceHeight)
+	//layer.AddActors(1, sketch.sourceWidth, sketch.sourceHeight)
 
 	return &layer
 }
@@ -38,18 +45,22 @@ func (s *ContourLayer) AddActors(n, sourceWidth, sourceHeight int32) {
 				stepSize: 1,
 				color:    rl.NewColor(11, 35, 176, 50),
 			}
-		s.actors = append(s.actors, newActor)
+		s.actors[s.actorIndex] = newActor
+		s.actorIndex = (s.actorIndex + 1) % s.maxActors
 	}
 }
 
 func (s *ContourLayer) Update(ctx *RenderCtx) {
 	s.AddActors(100, ctx.SourceWidth, ctx.SourceHeight)
+	fmt.Printf("num actors = %d\n", len(s.actors))
 }
 
 func (s *ContourLayer) Draw(ctx *RenderCtx) {
 	rl.BeginBlendMode(rl.BlendAdditive)
 	for _, actor := range s.actors {
-		actor.Draw()
+		if actor != nil {
+			actor.Draw()
+		}
 	}
 	rl.EndBlendMode()
 }
diff --git a/sketch.go b/sketch.go
index a2dd3d2..7de9540 100644
--- a/sketch.go
+++ b/sketch.go
@@ -90,22 +90,28 @@ func (s *Sketch) AddColorLayer(name string, c rl.Color) {
 	s.AddLayer(name, colorLayer)
 }
 
-func (s *Sketch) Draw(ctx *RenderCtx) {
+func (s *Sketch) Redraw(ctx *RenderCtx) {
 	// render onto all layer textures
 	for _, instance := range s.layerToolsOrdered {
 		layer := instance.layer
-		layer.Update(ctx)
-		if instance.layer.IsDirty() {
-			rl.BeginTextureMode(instance.texture)
-			rl.PushMatrix()
-			layer.Draw(ctx)
-			rl.PopMatrix()
-			rl.EndTextureMode()
+		// ignore this layer entirely unless it's visible
+		if instance.config.visible {
+			layer.Update(ctx)
+			// re-render to texture if dirty
+			if instance.layer.IsDirty() {
+				rl.BeginTextureMode(instance.texture)
+				rl.PushMatrix()
+				layer.Draw(ctx)
+				rl.PopMatrix()
+				rl.EndTextureMode()
+			}
 		}
 	}
+}
 
-	// composite all layers to screen
+func (s *Sketch) Draw(ctx *RenderCtx) {
 
+	s.Redraw(ctx)
 
 	// copy from full texture for compositing, with vertical flipping
 	src := rl.Rectangle {
@@ -122,7 +128,6 @@ func (s *Sketch) Draw(ctx *RenderCtx) {
 	viewport := s.CalcViewport(ctx)
 
 	rl.BeginTextureMode(s.composite)
-	//rl.ClearBackground(rl.Black)
 	for _, instance := range s.layerToolsOrdered {
 		config := instance.config
 		if config.visible {