diff --git a/image_test.go b/image_test.go
index 0b5b5cbe0..796a378b6 100644
--- a/image_test.go
+++ b/image_test.go
@@ -1238,23 +1238,25 @@ func TestImageLinearFilterGlitch(t *testing.T) {
 	}
 	src.ReplacePixels(pix)
 
-	op := &DrawImageOptions{}
-	op.GeoM.Scale(scale, 1)
-	op.Filter = FilterLinear
-	dst.DrawImage(src, op)
+	for _, f := range []Filter{FilterNearest, FilterLinear} {
+		op := &DrawImageOptions{}
+		op.GeoM.Scale(scale, 1)
+		op.Filter = f
+		dst.DrawImage(src, op)
 
-	for j := 1; j < h-1; j++ {
-		offset := int(math.Ceil(scale))
-		for i := offset; i < int(math.Floor(w*scale))-offset; i++ {
-			got := dst.At(i, j).(color.RGBA)
-			var want color.RGBA
-			if j < 3 {
-				want = color.RGBA{0xff, 0xff, 0xff, 0xff}
-			} else {
-				want = color.RGBA{0, 0, 0, 0xff}
-			}
-			if got != want {
-				t.Errorf("src.At(%d, %d): got: %v, want: %v", i, j, got, want)
+		for j := 1; j < h-1; j++ {
+			offset := int(math.Ceil(scale))
+			for i := offset; i < int(math.Floor(w*scale))-offset; i++ {
+				got := dst.At(i, j).(color.RGBA)
+				var want color.RGBA
+				if j < 3 {
+					want = color.RGBA{0xff, 0xff, 0xff, 0xff}
+				} else {
+					want = color.RGBA{0, 0, 0, 0xff}
+				}
+				if got != want {
+					t.Errorf("src.At(%d, %d): filter: %d, got: %v, want: %v", i, j, f, got, want)
+				}
 			}
 		}
 	}
diff --git a/internal/driver/compositemode.go b/internal/driver/compositemode.go
index 1bf983a7f..0b0237de2 100644
--- a/internal/driver/compositemode.go
+++ b/internal/driver/compositemode.go
@@ -21,7 +21,8 @@ import (
 type CompositeMode int
 
 const (
-	CompositeModeSourceOver CompositeMode = iota // This value must be 0 (= initial value)
+	CompositeModeUnknown    CompositeMode = iota - 1
+	CompositeModeSourceOver               // This value must be 0 (= initial value)
 	CompositeModeClear
 	CompositeModeCopy
 	CompositeModeDestination
@@ -34,7 +35,6 @@ const (
 	CompositeModeDestinationAtop
 	CompositeModeXor
 	CompositeModeLighter
-	CompositeModeUnknown
 
 	CompositeModeMax = CompositeModeLighter
 )
diff --git a/internal/graphicscommand/command.go b/internal/graphicscommand/command.go
index a10667d19..1ba606f13 100644
--- a/internal/graphicscommand/command.go
+++ b/internal/graphicscommand/command.go
@@ -265,7 +265,61 @@ type drawTrianglesCommand struct {
 }
 
 func (c *drawTrianglesCommand) String() string {
-	return fmt.Sprintf("draw-triangles: dst: %p <- src: %p, colorm: %v, mode %d, filter: %d, address: %d", c.dst, c.src, c.color, c.mode, c.filter, c.address)
+	mode := ""
+	switch c.mode {
+	case driver.CompositeModeSourceOver:
+		mode = "source-over"
+	case driver.CompositeModeClear:
+		mode = "clear"
+	case driver.CompositeModeCopy:
+		mode = "copy"
+	case driver.CompositeModeDestination:
+		mode = "destination"
+	case driver.CompositeModeDestinationOver:
+		mode = "destination-over"
+	case driver.CompositeModeSourceIn:
+		mode = "source-in"
+	case driver.CompositeModeDestinationIn:
+		mode = "destination-in"
+	case driver.CompositeModeSourceOut:
+		mode = "source-out"
+	case driver.CompositeModeDestinationOut:
+		mode = "destination-out"
+	case driver.CompositeModeSourceAtop:
+		mode = "source-atop"
+	case driver.CompositeModeDestinationAtop:
+		mode = "destination-atop"
+	case driver.CompositeModeXor:
+		mode = "xor"
+	case driver.CompositeModeLighter:
+		mode = "lighter"
+	default:
+		panic(fmt.Sprintf("graphicscommand: invalid composite mode: %d", c.mode))
+	}
+
+	filter := ""
+	switch c.filter {
+	case driver.FilterNearest:
+		filter = "nearest"
+	case driver.FilterLinear:
+		filter = "linear"
+	case driver.FilterScreen:
+		filter = "screen"
+	default:
+		panic(fmt.Sprintf("graphicscommand: invalid filter: %d", c.filter))
+	}
+
+	address := ""
+	switch c.address {
+	case driver.AddressClampToZero:
+		address = "clamp_to_zero"
+	case driver.AddressRepeat:
+		address = "repeat"
+	default:
+		panic(fmt.Sprintf("graphicscommand: invalid address: %d", c.address))
+	}
+
+	return fmt.Sprintf("draw-triangles: dst: %d <- src: %d, colorm: %v, mode %s, filter: %s, address: %s", c.dst.id, c.src.id, c.color, mode, filter, address)
 }
 
 // Exec executes the drawTrianglesCommand.
@@ -334,7 +388,7 @@ type replacePixelsCommand struct {
 }
 
 func (c *replacePixelsCommand) String() string {
-	return fmt.Sprintf("replace-pixels: dst: %p, x: %d, y: %d, width: %d, height: %d", c.dst, c.x, c.y, c.width, c.height)
+	return fmt.Sprintf("replace-pixels: dst: %d, x: %d, y: %d, width: %d, height: %d", c.dst.id, c.x, c.y, c.width, c.height)
 }
 
 // Exec executes the replacePixelsCommand.
@@ -377,7 +431,7 @@ func (c *pixelsCommand) Exec(indexOffset int) error {
 }
 
 func (c *pixelsCommand) String() string {
-	return fmt.Sprintf("pixels: img: %p", c.img)
+	return fmt.Sprintf("pixels: image: %d", c.img.id)
 }
 
 func (c *pixelsCommand) NumVertices() int {
@@ -404,7 +458,7 @@ type disposeCommand struct {
 }
 
 func (c *disposeCommand) String() string {
-	return fmt.Sprintf("dispose: target: %p", c.target)
+	return fmt.Sprintf("dispose: target: %d", c.target.id)
 }
 
 // Exec executes the disposeCommand.
@@ -439,7 +493,7 @@ type newImageCommand struct {
 }
 
 func (c *newImageCommand) String() string {
-	return fmt.Sprintf("new-image: result: %p, width: %d, height: %d", c.result, c.width, c.height)
+	return fmt.Sprintf("new-image: result: %d, width: %d, height: %d", c.result.id, c.width, c.height)
 }
 
 // Exec executes a newImageCommand.
@@ -478,7 +532,7 @@ type newScreenFramebufferImageCommand struct {
 }
 
 func (c *newScreenFramebufferImageCommand) String() string {
-	return fmt.Sprintf("new-screen-framebuffer-image: result: %p, width: %d, height: %d", c.result, c.width, c.height)
+	return fmt.Sprintf("new-screen-framebuffer-image: result: %d, width: %d, height: %d", c.result.id, c.width, c.height)
 }
 
 // Exec executes a newScreenFramebufferImageCommand.
diff --git a/internal/graphicscommand/image.go b/internal/graphicscommand/image.go
index 2fe34a4ac..725b2d07e 100644
--- a/internal/graphicscommand/image.go
+++ b/internal/graphicscommand/image.go
@@ -37,7 +37,17 @@ type Image struct {
 	internalWidth  int
 	internalHeight int
 	screen         bool
-	lastCommand    lastCommand
+	id             int
+
+	lastCommand lastCommand
+}
+
+var nextID = 1
+
+func genNextID() int {
+	id := nextID
+	nextID++
+	return id
 }
 
 // NewImage returns a new image.
@@ -49,6 +59,7 @@ func NewImage(width, height int) *Image {
 		height:         height,
 		internalWidth:  graphics.InternalImageSize(width),
 		internalHeight: graphics.InternalImageSize(height),
+		id:             genNextID(),
 	}
 	c := &newImageCommand{
 		result: i,
@@ -66,6 +77,7 @@ func NewScreenFramebufferImage(width, height int) *Image {
 		internalWidth:  graphics.InternalImageSize(width),
 		internalHeight: graphics.InternalImageSize(height),
 		screen:         true,
+		id:             genNextID(),
 	}
 	c := &newScreenFramebufferImageCommand{
 		result: i,