diff --git a/main.go b/main.go
index 698d88d..e0fd15e 100644
--- a/main.go
+++ b/main.go
@@ -15,10 +15,17 @@ import (
 const (
 	targetWidth  = 800
 	targetHeight = 600
-	sourceScale  = 1
+	sourceScale  = 10
 	snapshotsDir = "snapshots"
 )
 
+type TextureCam struct {
+	SourceWidth int
+	SourceHeight int
+	LookAt rl.Vector2
+	Zoom float32
+}
+
 func main() {
 
 	sourceWidth  := sourceScale * targetWidth
@@ -32,7 +39,7 @@ func main() {
 		os.Exit(1)
 	}
 
-	rl.SetConfigFlags(rl.FlagWindowHighdpi & rl.FlagMsaa4xHint)
+	rl.SetConfigFlags(rl.FlagMsaa4xHint)
 	rl.InitWindow(targetWidth, targetHeight, "sumi sierpinski arrow")
 
 	log.Printf("screen=%dx%d render=%dx%d",
@@ -42,11 +49,11 @@ func main() {
 
 	// point at source center
 	// put source center at center of screen
-	var camera = rl.Camera2D {
-		Target:   rl.Vector2{X: float32(targetWidth) / 2, Y: float32(targetHeight) / 2},
-		Offset:   rl.Vector2{},
-		Zoom:     1.0,
-		Rotation: 0,
+	var camera = TextureCam {
+		LookAt: rl.Vector2 { X: float32(sourceWidth) / 2.0, Y: float32(sourceHeight) / 2.0 },
+		Zoom: 1.0,
+		SourceWidth: sourceWidth,
+		SourceHeight: sourceHeight,
 	}
 
 	/*
@@ -85,7 +92,6 @@ func main() {
 	}
 
 	for !rl.WindowShouldClose() {
-		updateCamera(&camera)
 
 		// begin drawing
 		t := time.Since(t0).Seconds()
@@ -98,9 +104,11 @@ func main() {
 			SourceHeight: int32(sourceHeight),
 			Time:         t,
 			Ports:        ports.Eval(t),
-			Cam:          camera,
+			Cam:          &camera,
 		}
 
+		sketch.Update(renderCtx)
+
 		/**
 		MAIN DRAWING
 		 **/
@@ -131,6 +139,7 @@ type FieldSketch struct {
 	Field Field
 }
 
+/*
 func (s *FieldSketch) Draw(ctx *RenderCtx) {
 	fmt.Printf("drawing field")
 	for x := range ctx.TargetWidth {
@@ -143,6 +152,7 @@ func (s *FieldSketch) Draw(ctx *RenderCtx) {
 		}
 	}
 }
+*/
 
 type ContourLayer struct {
 	field  Field
@@ -196,40 +206,6 @@ func RandRadialVec(rng *rand.Rand, minRadius float32, maxRadius float32, loAngle
 	return rl.Vector2{X: float32(r * math.Cos(rad)), Y: float32(r * math.Sin(rad))}
 }
 
-func updateCamera(camera *rl.Camera2D) {
-	// Get the world point that is under the mouse
-	mouseVec2 := rl.GetMousePosition()
-
-	if rl.IsMouseButtonDown(rl.MouseRightButton) {
-		// get mouse delta from last frame
-		delta := rl.GetMouseDelta()
-		// compute the amount to move scaled by the camera zoom
-		delta = rl.Vector2Scale(delta, -1.0/camera.Zoom)
-		delta.Y = -delta.Y
-		camera.Target = rl.Vector2Add(camera.Target, delta)
-	}
-	// Zoom based on mouse wheel
-	wheel := rl.GetMouseWheelMove()
-	if wheel != 0 {
-		mouseWorldPos := rl.GetScreenToWorld2D(mouseVec2, *camera)
-
-		// Set the offset to where the mouse is
-		camera.Offset = mouseVec2
-
-		// Set the target to match, so that the camera maps the world space point
-		// under the cursor to the screen space point under the cursor at any zoom
-		camera.Target = mouseWorldPos
-
-		// Zoom increment
-		const zoomIncrement float32 = 0.125
-
-		camera.Zoom += (wheel * zoomIncrement)
-		if camera.Zoom < zoomIncrement {
-			camera.Zoom = zoomIncrement
-		}
-	}
-}
-
 type Worm struct {
 	position   rl.Vector2
 	angles     []float32
diff --git a/sketch.go b/sketch.go
index 906361f..f9d7420 100644
--- a/sketch.go
+++ b/sketch.go
@@ -1,7 +1,7 @@
 package main
 
 import (
-	"fmt"
+	"math"
 	"github.com/gen2brain/raylib-go/raylib"
 )
 
@@ -10,36 +10,17 @@ type Sketch struct {
 }
 
 func NewSketch() Sketch {
-	return Sketch {
+	return Sketch{
 		layerTools: make(map[string]LayerTools),
 	}
 }
 
 func (s *Sketch) CreateLayer(name string, layer Layer, sourceWidth int32, sourceHeight int32) {
 	texture := rl.LoadRenderTexture(sourceWidth, sourceHeight)
-	s.layerTools[name] = LayerTools {
-		name: name,
+	s.layerTools[name] = LayerTools{
+		name:    name,
 		texture: &texture,
-		layer: layer,
-	}
-}
-
-func LayerViewRect(ctx *RenderCtx) rl.Rectangle {
-
-	z := ctx.Cam.Zoom
-
-	// get the viewport width in texture space
-	viewportWidth  := float32(ctx.TargetWidth) / z
-	viewportHeight := float32(ctx.TargetHeight) / z
-
-	x := rl.Clamp(ctx.Cam.Target.X - viewportWidth/2, 0, float32(ctx.SourceWidth) - viewportWidth/2.0)
-	y := rl.Clamp(ctx.Cam.Target.Y - viewportHeight/2, 0, float32(ctx.SourceHeight) - viewportHeight/2.0)
-
-	return rl.Rectangle{
-		X: x,
-		Y: y,
-		Width:  viewportWidth,
-		Height: viewportHeight,
+		layer:   layer,
 	}
 }
 
@@ -52,36 +33,68 @@ func (s *Sketch) Draw(ctx *RenderCtx) {
 		layer.Draw(ctx)
 		rl.EndTextureMode()
 	}
+
 	// composite all layers to screen
 
-	//ClampCameraToLayer(ctx)
-
-	//view := LayerViewRect(ctx)
-	src := rl.Rectangle {
-		X: 0,
-		Y: 0,
-		Width: float32(ctx.SourceWidth),
-		Height: -float32(ctx.SourceHeight),
-	}
-
-	dst := rl.Rectangle {
-		X: 0,
-		Y: 0,
-		Width: float32(ctx.TargetWidth),
+	screen := rl.Rectangle {
+		X:      0,
+		Y:      0,
+		Width:  float32(ctx.TargetWidth),
 		Height: float32(ctx.TargetHeight),
 	}
 
-	fmt.Printf("src = %v, dst  %v\n", src, dst)
+	viewport := s.CalcViewport(ctx)
 
 	for _, instance := range s.layerTools {
-		rl.DrawTexturePro(instance.texture.Texture, src, dst, rl.Vector2{}, 0, rl.White)
+		rl.DrawTexturePro(instance.texture.Texture, viewport, screen, rl.Vector2{}, 0, rl.White)
 	}
-	
+
+}
+
+func (s *Sketch) CalcViewport(ctx *RenderCtx) rl.Rectangle {
+	viewportWidth := rl.Clamp(float32(ctx.SourceWidth) / ctx.Cam.Zoom, 0, float32(ctx.SourceWidth))
+	viewportHeight := rl.Clamp(float32(ctx.SourceHeight) / ctx.Cam.Zoom, 0, float32(ctx.SourceHeight))
+	return rl.Rectangle{
+		X:      rl.Clamp(ctx.Cam.LookAt.X - viewportWidth/2.0, 0, float32(ctx.SourceWidth)-viewportWidth),
+		Y:      rl.Clamp(ctx.Cam.LookAt.Y - viewportHeight/2.0, 0, float32(ctx.SourceHeight)-viewportHeight),
+		Width:  float32(viewportWidth),
+		Height: -float32(viewportHeight),
+	}
+}
+
+func (s *Sketch) Update(ctx *RenderCtx) {
+	if rl.IsMouseButtonDown(rl.MouseRightButton) {
+		// get mouse delta from last frame
+		delta := rl.GetMouseDelta()
+		// compute the amount to move scaled by the camera zoom
+		delta = rl.Vector2Scale(delta, -sourceScale/ctx.Cam.Zoom)
+		delta.Y = -delta.Y
+		ctx.Cam.LookAt = rl.Vector2Add(ctx.Cam.LookAt, delta)
+	}
+
+	// clamp LookAt to be somewhere on the texture
+	ctx.Cam.LookAt.X = rl.Clamp(ctx.Cam.LookAt.X, 0, float32(ctx.SourceWidth-1))
+	ctx.Cam.LookAt.Y = rl.Clamp(ctx.Cam.LookAt.Y, 0, float32(ctx.SourceHeight-1))
+
+	// Zoom based on mouse wheel
+	wheel := rl.GetMouseWheelMove()
+	if wheel != 0 {
+		const zoomIncrement float32 = 0.05
+		if wheel > 0 {
+			ctx.Cam.Zoom *= 1+zoomIncrement
+		} else {
+			ctx.Cam.Zoom *= 1-zoomIncrement
+		}
+	}
+
+	// clamp zoom to > 1 so we don't ever zoom out more than necessary
+	ctx.Cam.Zoom = rl.Clamp(ctx.Cam.Zoom, 1, math.MaxInt64)
+
 }
 
 type LayerTools struct {
-	name string
-	layer Layer
+	name    string
+	layer   Layer
 	texture *rl.RenderTexture2D
 }
 
@@ -91,7 +104,7 @@ type Layer interface {
 	Draw(ctx *RenderCtx)
 }
 
-type TestPattern struct { }
+type TestPattern struct{}
 
 func DrawGrid(spacing int32, halfExtent int32) {
 	col := rl.Color{R: 220, G: 220, B: 220, A: 255}
@@ -107,13 +120,13 @@ func DrawGrid(spacing int32, halfExtent int32) {
 func (tp *TestPattern) Draw(ctx *RenderCtx) {
 
 	rl.ClearBackground(rl.Black)
-	centerX := float32(ctx.SourceWidth)/2
-	centerY := float32(ctx.SourceHeight)/2
+	centerX := float32(ctx.SourceWidth) / 2
+	centerY := float32(ctx.SourceHeight) / 2
 
-	rl.DrawRectangleRec(rl.Rectangle { X: 0, Y: 0, Width: centerX, Height: centerY }, rl.Red)
-	rl.DrawRectangleRec(rl.Rectangle { X: centerX, Y: 0, Width: centerX, Height: centerY }, rl.Green)
-	rl.DrawRectangleRec(rl.Rectangle { X: 0, Y: centerY, Width: centerX, Height: centerY }, rl.Blue)
-	rl.DrawRectangleRec(rl.Rectangle { X: centerX, Y: centerY, Width: centerX, Height: centerY }, rl.White)
+	rl.DrawRectangleRec(rl.Rectangle{X: 0, Y: 0, Width: centerX, Height: centerY}, rl.Red)
+	rl.DrawRectangleRec(rl.Rectangle{X: centerX, Y: 0, Width: centerX, Height: centerY}, rl.Green)
+	rl.DrawRectangleRec(rl.Rectangle{X: 0, Y: centerY, Width: centerX, Height: centerY}, rl.Blue)
+	rl.DrawRectangleRec(rl.Rectangle{X: centerX, Y: centerY, Width: centerX, Height: centerY}, rl.White)
 
 	rl.DrawLine(0, 0, ctx.SourceWidth, ctx.SourceHeight, rl.Black)
 
@@ -126,7 +139,6 @@ func (tp *TestPattern) Draw(ctx *RenderCtx) {
 	rl.PopMatrix()
 }
 
-
 /** Ports **/
 
 type Ports map[string]Signal
@@ -151,9 +163,9 @@ func (p Ports) Eval(t float64) map[string]float64 {
 type RenderCtx struct {
 	TargetWidth  int32
 	TargetHeight int32
-	SourceWidth int32
+	SourceWidth  int32
 	SourceHeight int32
-	Time   float64
-	Ports  map[string]float64
-	Cam    rl.Camera2D
+	Time         float64
+	Ports        map[string]float64
+	Cam          *TextureCam
 }