(Experimental) Run Length Encoding for Levels

Finally add a second option for Chunk MapAccessor implementation besides the
MapAccessor. The RLEAccessor is basically a MapAccessor that will compress
your drawing with Run Length Encoding (RLE) in the on-disk format in the ZIP
file.

This slashes the file sizes of most levels:

* Shapeshifter: 21.8 MB -> 8.1 MB
* Jungle: 10.4 MB -> 4.1 MB
* Zoo: 2.8 MB -> 1.3 MB

Implementation details:

* The RLE binary format for Chunks is a stream of Uvarint pairs storing the
  palette index number and the number of pixels to repeat it (along the Y,X
  axis of the chunk).
    * Null colors are represented by a Uvarint that decodes to 0xFFFF
      or 65535 in decimal.
    * Gameplay logic currently limits maps to 256 colors.
* The default for newly created chunks in-game will be RLE by default.
* Its in-memory representation is still a MapAccessor (a map of absolute
  world coordinates to palette index).
* The game can still open and play legacy MapAccessor maps.
* On save in the editor, the game will upgrade/convert MapAccessor chunks over
  to RLEAccessors, improving on your level's file size with a simple re-save.

Current Bugs

* On every re-save to RLE, one pixel is lost in the bottom-right corner of
  each chunk. Each subsequent re-save loses one more pixel to the left, so what
  starts as a single pixel per chunk slowly evolves into a horizontal line.
* Some pixels smear vertically as well.
* Off-by-negative-one errors when some chunks Iter() their pixels but compute
  a relative coordinate of (-1,0)! Some mismatch between the stored world coords
  of a pixel inside the chunk vs. the chunk's assigned coordinate by the Chunker:
  certain combinations of chunk coord/abs coord.

To Do

* The `doodad touch` command should re-save existing levels to upgrade them.

cmd/doodle/main.go

@@ -101,6 +101,11 @@ func main() {
 			Name:  "chdir",
 			Usage: "working directory for the game's runtime package",
 		},
+		&cli.BoolFlag{
+			Name:    "new",
+			Aliases: []string{"n"},
+			Usage:   "open immediately to the level editor",
+		},
 		&cli.BoolFlag{
 			Name:    "edit",
 			Aliases: []string{"e"},
@@ -248,6 +253,8 @@ func main() {
 
 		if c.Bool("guitest") {
 			game.Goto(&doodle.GUITestScene{})
+		} else if c.Bool("new") {
+			game.NewMap()
 		} else if filename != "" {
 			if c.Bool("edit") {
 				game.EditFile(filename)

pkg/balance/feature_flags.go

@@ -28,6 +28,12 @@ const (
 	// If you set both flags to false, level zipfiles will use the classic
 	// json chunk format as before on save.
 	BinaryChunkerEnabled = true
+
+	// Enable "v3" Run-Length Encoding for level chunker.
+	//
+	// This only supports Zipfile levels and will use the ".bin" format
+	// enabled by the previous setting.
+	RLEBinaryChunkerEnabled = true
 )
 
 // Feature Flags to turn on/off experimental content.

pkg/level/chunk.go

@@ -24,6 +24,9 @@ const (
 	GridType
 )
 
+// Default chunk type for newly created chunks (was MapType).
+const DefaultChunkType = RLEType
+
 // Chunk holds a single portion of the pixel canvas.
 type Chunk struct {
 	Type uint64 // map vs. 2D array.
@@ -55,7 +58,6 @@ type JSONChunk struct {
 // Accessor provides a high-level API to interact with absolute pixel coordinates
 // while abstracting away the details of how they're stored.
 type Accessor interface {
-	SetChunkCoordinate(render.Point, uint8)
 	Inflate(*Palette) error
 	Iter() <-chan Pixel
 	IterViewport(viewport render.Rect) <-chan Pixel
@@ -69,10 +71,11 @@ type Accessor interface {
 
 // NewChunk creates a new chunk.
 func NewChunk() *Chunk {
-	return &Chunk{
+	var c = &Chunk{
-		Type:     RLEType,
+		Type: RLEType,
-		Accessor: NewRLEAccessor(),
 	}
+	c.Accessor = NewRLEAccessor(c)
+	return c
 }
 
 // Texture will return a cached texture for the rendering engine for this
@@ -335,6 +338,9 @@ func (c *Chunk) Usage(size int) float64 {
 // parse the inner details.
 //
 // DEPRECATED in favor of binary marshalling.
+//
+// Only supports MapAccessor chunk types, which was the only one supported
+// before this function was deprecated.
 func (c *Chunk) UnmarshalJSON(b []byte) error {
 	// Parse it generically so we can hand off the inner "data" object to the
 	// right accessor for unmarshalling.
@@ -346,7 +352,7 @@ func (c *Chunk) UnmarshalJSON(b []byte) error {
 
 	switch c.Type {
 	case MapType:
-		c.Accessor = NewMapAccessor()
+		c.Accessor = NewMapAccessor(c)
 		if unmarshaler, ok := c.Accessor.(json.Unmarshaler); ok {
 			return unmarshaler.UnmarshalJSON(generic.Data)
 		}
@@ -393,12 +399,12 @@ func (c *Chunk) UnmarshalBinary(b []byte) error {
 	// Decode the rest of the byte stream.
 	switch chunkType {
 	case MapType:
-		c.Accessor = NewMapAccessor()
+		c.Type = MapType
-		c.Accessor.SetChunkCoordinate(c.Point, c.Size)
+		c.Accessor = NewMapAccessor(c)
 		return c.Accessor.UnmarshalBinary(reader.Bytes())
 	case RLEType:
-		c.Accessor = NewRLEAccessor()
+		c.Type = RLEType
-		c.Accessor.SetChunkCoordinate(c.Point, c.Size)
+		c.Accessor = NewRLEAccessor(c)
 		return c.Accessor.UnmarshalBinary(reader.Bytes())
 	default:
 		return fmt.Errorf("Chunk.UnmarshalJSON: unsupported chunk type '%d'", c.Type)

pkg/level/chunk_map.go

@@ -16,23 +16,22 @@ import (
 // MapAccessor implements a chunk accessor by using a map of points to their
 // palette indexes. This is the simplest accessor and is best for sparse chunks.
 type MapAccessor struct {
-	coord render.Point `json:"-"` // chunk coordinate, assigned by Chunker
+	chunk *Chunk // Pointer to parent struct, for its Size and Point
-	size  uint8        `json:"-"` // chunk size, assigned by Chunker
 	grid  map[render.Point]*Swatch
 	mu    sync.RWMutex
 }
 
 // NewMapAccessor initializes a MapAccessor.
-func NewMapAccessor() *MapAccessor {
+func NewMapAccessor(chunk *Chunk) *MapAccessor {
 	return &MapAccessor{
-		grid: map[render.Point]*Swatch{},
+		chunk: chunk,
+		grid:  map[render.Point]*Swatch{},
 	}
 }
 
-// SetChunkCoordinate receives our chunk's coordinate from the Chunker.
+// Reset the MapAccessor.
-func (a *MapAccessor) SetChunkCoordinate(p render.Point, size uint8) {
+func (a *MapAccessor) Reset() {
-	a.coord = p
+	a.grid = map[render.Point]*Swatch{}
-	a.size = size
 }
 
 // Inflate the sparse swatches from their palette indexes.

pkg/level/chunk_rle.go

@@ -1,10 +1,7 @@
 package level
 
 import (
-	"bytes"
+	"git.kirsle.net/SketchyMaze/doodle/pkg/level/rle"
-	"encoding/binary"
-	"errors"
-
 	"git.kirsle.net/SketchyMaze/doodle/pkg/log"
 	"git.kirsle.net/go/render"
 )
@@ -12,22 +9,18 @@ import (
 // RLEAccessor implements a chunk accessor which stores its on-disk format using
 // Run Length Encoding (RLE), but in memory behaves equivalently to the MapAccessor.
 type RLEAccessor struct {
-	acc *MapAccessor
+	chunk *Chunk // parent Chunk, for its Size and Point
+	acc   *MapAccessor
 }
 
 // NewRLEAccessor initializes a RLEAccessor.
-func NewRLEAccessor() *RLEAccessor {
+func NewRLEAccessor(chunk *Chunk) *RLEAccessor {
 	return &RLEAccessor{
-		acc: NewMapAccessor(),
+		chunk: chunk,
+		acc:   NewMapAccessor(chunk),
 	}
 }
 
-// SetChunkCoordinate receives our chunk's coordinate from the Chunker.
-func (a *RLEAccessor) SetChunkCoordinate(p render.Point, size uint8) {
-	a.acc.coord = p
-	a.acc.size = size
-}
-
 // Inflate the sparse swatches from their palette indexes.
 func (a *RLEAccessor) Inflate(pal *Palette) error {
 	return a.acc.Inflate(pal)
@@ -63,23 +56,6 @@ func (a *RLEAccessor) Delete(p render.Point) error {
 	return a.acc.Delete(p)
 }
 
-// Make2DChunkGrid creates a 2D map of uint64 pointers matching the square dimensions of the given size.
-//
-// It is used by the RLEAccessor to flatten a chunk into a grid for run-length encoding.
-func Make2DChunkGrid(size int) ([][]*uint64, error) {
-	// Sanity check if the chunk was properly initialized.
-	if size == 0 {
-		return nil, errors.New("chunk not initialized correctly with its size and coordinate")
-	}
-
-	var grid = make([][]*uint64, size)
-	for i := 0; i < size; i++ {
-		grid[i] = make([]*uint64, size)
-	}
-
-	return grid, nil
-}
-
 /*
 MarshalBinary converts the chunk data to a binary representation.
 
@@ -93,8 +69,8 @@ formatted as such:
 func (a *RLEAccessor) MarshalBinary() ([]byte, error) {
 	// Flatten the chunk out into a full 2D array of all its points.
 	var (
-		size      = int(a.acc.size)
+		size      = int(a.chunk.Size)
-		grid, err = Make2DChunkGrid(size)
+		grid, err = rle.NewGrid(size)
 	)
 	if err != nil {
 		return nil, err
@@ -104,50 +80,18 @@ func (a *RLEAccessor) MarshalBinary() ([]byte, error) {
 	for px := range a.Iter() {
 		var (
 			point    = render.NewPoint(px.X, px.Y)
-			relative = RelativeCoordinate(point, a.acc.coord, a.acc.size)
+			relative = RelativeCoordinate(point, a.chunk.Point, a.chunk.Size)
-			ptr      = uint64(px.PaletteIndex)
+			ptr      = uint64(px.Swatch.Index())
 		)
+
+		// TODO: sometimes we get a -1 value in X or Y, not sure why.
+		if relative.X < 0 || relative.Y < 0 {
+			continue
+		}
 		grid[relative.Y][relative.X] = &ptr
 	}
 
-	// log.Error("2D GRID:\n%+v", grid)
+	return grid.Compress()
-
-	// Run-length encode the grid.
-	var (
-		compressed []byte
-		firstColor = true
-		lastColor  uint64
-		runLength  uint64
-	)
-	for _, row := range grid {
-		for _, color := range row {
-			var index uint64
-			if color == nil {
-				index = 0xFF
-			}
-
-			if firstColor {
-				lastColor = index
-				runLength = 1
-				firstColor = false
-				continue
-			}
-
-			if index != lastColor {
-				compressed = binary.AppendUvarint(compressed, index)
-				compressed = binary.AppendUvarint(compressed, runLength)
-				lastColor = index
-				runLength = 1
-				continue
-			}
-
-			runLength++
-		}
-	}
-
-	log.Error("RLE compressed: %v", compressed)
-
-	return compressed, nil
 }
 
 // UnmarshalBinary will decode a compressed RLEAccessor byte stream.
@@ -158,10 +102,39 @@ func (a *RLEAccessor) UnmarshalBinary(compressed []byte) error {
 	// New format: decompress the byte stream.
 	log.Debug("RLEAccessor.Unmarshal: Reading %d bytes of compressed chunk data", len(compressed))
 
-	// Prepare the 2D grid to decompress the RLE stream into.
+	grid, err := rle.NewGrid(int(a.chunk.Size))
+	if err != nil {
+		return err
+	}
+
+	if err := grid.Decompress(compressed); err != nil {
+		return err
+	}
+
+	// Load the grid into our MapAccessor.
+	a.acc.Reset()
+	for y, row := range grid {
+		for x, col := range row {
+			if col == nil {
+				continue
+			}
+
+			// TODO: x-1 to avoid the level creeping to the right every save,
+			// not sure on the root cause! RLEAccessor Decompress?
+			abs := FromRelativeCoordinate(render.NewPoint(x, y), a.chunk.Point, a.chunk.Size)
+			abs.X -= 1
+			a.acc.grid[abs] = NewSparseSwatch(int(*col))
+		}
+	}
+
+	return nil
+}
+
+/*
+// Prepare the 2D grid to decompress the RLE stream into.
 	var (
-		size         = int(a.acc.size)
+		size         = int(a.chunk.Size)
-		_, err       = Make2DChunkGrid(size)
+		_, err       = rle.NewGrid(size)
 		x, y, cursor int
 	)
 	if err != nil {
@@ -181,6 +154,8 @@ func (a *RLEAccessor) UnmarshalBinary(compressed []byte) error {
 			break
 		}
 
+		log.Warn("RLE index %d for %dpx", paletteIndex, repeatCount)
+
 		for i := uint64(0); i < repeatCount; i++ {
 			cursor++
 			if cursor%size == 0 {
@@ -196,6 +171,4 @@ func (a *RLEAccessor) UnmarshalBinary(compressed []byte) error {
 			}
 		}
 	}
-
+*/
-	return nil
-}

pkg/level/chunk_test.go

@@ -129,8 +129,10 @@ func TestChunker(t *testing.T) {
 
 // Test the map chunk accessor.
 func TestMapAccessor(t *testing.T) {
-	a := level.NewMapAccessor()
+	var (
-	_ = a
+		c = level.NewChunk()
+		a = level.NewMapAccessor(c)
+	)
 
 	// Test action types
 	var (

pkg/level/chunker.go

@@ -74,7 +74,6 @@ func (c *Chunker) Inflate(pal *Palette) error {
 	for coord, chunk := range c.Chunks {
 		chunk.Point = coord
 		chunk.Size = c.Size
-		chunk.SetChunkCoordinate(chunk.Point, chunk.Size)
 		chunk.Inflate(pal)
 	}
 	return nil
@@ -326,7 +325,7 @@ func (c *Chunker) GetChunk(p render.Point) (*Chunk, bool) {
 
 	// Hit the zipfile for it.
 	if c.Zipfile != nil {
-		if chunk, err := ChunkFromZipfile(c.Zipfile, c.Layer, p); err == nil {
+		if chunk, err := c.ChunkFromZipfile(p); err == nil {
 			// log.Debug("GetChunk(%s) cache miss, read from zip", p)
 			c.SetChunk(p, chunk)       // cache it
 			c.logChunkAccess(p, chunk) // for the LRU cache
@@ -446,7 +445,6 @@ func (c *Chunker) FreeCaches() int {
 // This function should be the singular writer to the chunk cache.
 func (c *Chunker) SetChunk(p render.Point, chunk *Chunk) {
 	c.chunkMu.Lock()
-	chunk.SetChunkCoordinate(p, chunk.Size)
 	c.Chunks[p] = chunk
 	c.chunkMu.Unlock()
 
@@ -617,6 +615,32 @@ func (c *Chunker) ChunkCoordinate(abs render.Point) render.Point {
 // - And relative inside that chunk, the pixel is at (24,)
 func RelativeCoordinate(abs render.Point, chunkCoord render.Point, chunkSize uint8) render.Point {
 	// Pixel coordinate offset.
+	var (
+		size   = int(chunkSize)
+		offset = render.Point{
+			X: chunkCoord.X * size,
+			Y: chunkCoord.Y * size,
+		}
+		point = render.Point{
+			X: abs.X - offset.X,
+			Y: abs.Y - offset.Y,
+		}
+	)
+
+	if point.X < 0 || point.Y < 0 {
+		log.Error("RelativeCoordinate: X < 0! abs=%s rel=%s chunk=%s size=%d", abs, point, chunkCoord, chunkSize)
+		log.Error("RelativeCoordinate(2): size=%d offset=%s point=%s", size, offset, point)
+	}
+
+	return point
+}
+
+// FromRelativeCoordinate is the inverse of RelativeCoordinate.
+//
+// With a chunk size of 128 and a relative coordinate like (8, 12),
+// this function will return the absolute world coordinates based
+// on your chunk.Point's placement in the level.
+func FromRelativeCoordinate(rel render.Point, chunkCoord render.Point, chunkSize uint8) render.Point {
 	var (
 		size   = int(chunkSize)
 		offset = render.Point{
@@ -626,8 +650,8 @@ func RelativeCoordinate(abs render.Point, chunkCoord render.Point, chunkSize uin
 	)
 
 	return render.Point{
-		X: abs.X - offset.X,
+		X: rel.X + offset.X,
-		Y: abs.Y - offset.Y,
+		Y: rel.Y + offset.Y,
 	}
 }
 

pkg/level/chunker_migrate.go

@@ -0,0 +1,67 @@
+package level
+
+import (
+	"runtime"
+	"sync"
+
+	"git.kirsle.net/SketchyMaze/doodle/pkg/balance"
+	"git.kirsle.net/SketchyMaze/doodle/pkg/log"
+)
+
+/* Functions to migrate Chunkers between different implementations. */
+
+// OptimizeChunkerAccessors will evaluate all of the chunks of your drawing
+// and possibly migrate them to a different Accessor implementation when
+// saving on disk.
+func (c *Chunker) OptimizeChunkerAccessors() {
+	c.chunkMu.Lock()
+	defer c.chunkMu.Unlock()
+
+	log.Info("Optimizing Chunker Accessors")
+
+	// TODO: parallelize this with goroutines
+	var (
+		chunks = make(chan *Chunk, len(c.Chunks))
+		wg     sync.WaitGroup
+	)
+
+	for range runtime.NumCPU() {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for chunk := range chunks {
+				var point = chunk.Point
+				log.Warn("Chunk %s is a: %d", point, chunk.Type)
+
+				// Upgrade all MapTypes into RLE compressed MapTypes?
+				if balance.RLEBinaryChunkerEnabled {
+					if chunk.Type == MapType {
+						log.Info("Optimizing chunk %s accessor from Map to RLE", point)
+						ma, _ := chunk.Accessor.(*MapAccessor)
+						rle := NewRLEAccessor(chunk).FromMapAccessor(ma)
+
+						c.Chunks[point].Type = RLEType
+						c.Chunks[point].Accessor = rle
+					}
+				}
+			}
+		}()
+	}
+
+	// Feed it the chunks.
+	for _, chunk := range c.Chunks {
+		chunks <- chunk
+	}
+
+	close(chunks)
+	wg.Wait()
+
+}
+
+// FromMapAccessor migrates from a MapAccessor to RLE.
+func (a *RLEAccessor) FromMapAccessor(ma *MapAccessor) *RLEAccessor {
+	return &RLEAccessor{
+		chunk: a.chunk,
+		acc:   ma,
+	}
+}

pkg/level/chunker_test.go

@@ -228,3 +228,98 @@ func TestViewportChunks(t *testing.T) {
 		}
 	}
 }
+
+func TestRelativeCoordinates(t *testing.T) {
+
+	var (
+		chunker = level.NewChunker(128)
+	)
+
+	type TestCase struct {
+		WorldCoord     render.Point
+		ChunkCoord     render.Point
+		ExpectRelative render.Point
+	}
+	var tests = []TestCase{
+		{
+			WorldCoord:     render.NewPoint(4, 8),
+			ExpectRelative: render.NewPoint(4, 8),
+		},
+		{
+			WorldCoord:     render.NewPoint(128, 128),
+			ExpectRelative: render.NewPoint(0, 0),
+		},
+		{
+			WorldCoord:     render.NewPoint(143, 144),
+			ExpectRelative: render.NewPoint(15, 16),
+		},
+		{
+			WorldCoord:     render.NewPoint(-105, -86),
+			ExpectRelative: render.NewPoint(23, 42),
+		},
+		{
+			WorldCoord:     render.NewPoint(-252, 264),
+			ExpectRelative: render.NewPoint(4, 8),
+		},
+
+		// These were seen breaking actual levels, at the corners of the chunk
+		{
+			WorldCoord:     render.NewPoint(511, 256),
+			ExpectRelative: render.NewPoint(127, 0), // was getting -1,0 in game
+		},
+		{
+			WorldCoord:     render.NewPoint(511, 512),
+			ChunkCoord:     render.NewPoint(4, 4),
+			ExpectRelative: render.NewPoint(127, 0), // was getting -1,0 in game
+		},
+		{
+			WorldCoord:     render.NewPoint(127, 384),
+			ChunkCoord:     render.NewPoint(1, 3),
+			ExpectRelative: render.NewPoint(-1, 0),
+		},
+	}
+	for i, test := range tests {
+		var (
+			chunkCoord     = test.ChunkCoord
+			actualRelative = level.RelativeCoordinate(
+				test.WorldCoord,
+				chunkCoord,
+				chunker.Size,
+			)
+			roundTrip = level.FromRelativeCoordinate(
+				actualRelative,
+				chunkCoord,
+				chunker.Size,
+			)
+		)
+
+		// compute expected chunk coord automatically?
+		if chunkCoord == render.Origin {
+			chunkCoord = chunker.ChunkCoordinate(test.WorldCoord)
+		}
+
+		if actualRelative != test.ExpectRelative {
+			t.Errorf("Test %d: world coord %s in chunk %s\n"+
+				"Expected RelativeCoordinate() to be: %s\n"+
+				"But it was: %s",
+				i,
+				test.WorldCoord,
+				chunkCoord,
+				test.ExpectRelative,
+				actualRelative,
+			)
+		}
+
+		if roundTrip != test.WorldCoord {
+			t.Errorf("Test %d: world coord %s in chunk %s\n"+
+				"Did not survive round trip! Expected: %s\n"+
+				"But it was: %s",
+				i,
+				test.WorldCoord,
+				chunkCoord,
+				test.WorldCoord,
+				roundTrip,
+			)
+		}
+	}
+}

pkg/level/chunker_zipfile.go

@@ -93,7 +93,7 @@ func (c *Chunker) MigrateZipfile(zf *zip.Writer) error {
 				}
 
 				// Verify that this chunk file in the old ZIP was not empty.
-				chunk, err := ChunkFromZipfile(c.Zipfile, c.Layer, point)
+				chunk, err := c.ChunkFromZipfile(point)
 				if err == nil && chunk.Len() == 0 {
 					log.Debug("Skip chunk %s (old zipfile chunk was empty)", coord)
 					continue
@@ -205,14 +205,20 @@ func (c *Chunk) ToZipfile(zf *zip.Writer, layer int, coord render.Point) error {
 }
 
 // ChunkFromZipfile loads a chunk from a zipfile.
-func ChunkFromZipfile(zf *zip.Reader, layer int, coord render.Point) (*Chunk, error) {
+func (c *Chunker) ChunkFromZipfile(coord render.Point) (*Chunk, error) {
 	// File names?
 	var (
+		zf    = c.Zipfile
+		layer = c.Layer
+
 		binfile  = fmt.Sprintf("chunks/%d/%s.bin", layer, coord)
 		jsonfile = fmt.Sprintf("chunks/%d/%s.json", layer, coord)
 		chunk    = NewChunk()
 	)
 
+	chunk.Point = coord
+	chunk.Size = c.Size
+
 	// Read from the new binary format.
 	if file, err := zf.Open(binfile); err == nil {
 		// log.Debug("Reading binary compressed chunk from %s", binfile)

pkg/level/fmt_maintenance.go

@@ -4,6 +4,21 @@ import "git.kirsle.net/SketchyMaze/doodle/pkg/log"
 
 // Maintenance functions for the file format on disk.
 
+// Vacuum runs any maintenance or migration tasks for the level at time of save.
+//
+// It will prune broken links between actors, or migrate internal data structures
+// to optimize storage on disk of its binary data.
+func (m *Level) Vacuum() error {
+	if links := m.PruneLinks(); links > 0 {
+		log.Debug("Vacuum: removed %d broken links between actors in this level.")
+	}
+
+	// Let the Chunker optimize accessor types.
+	m.Chunker.OptimizeChunkerAccessors()
+
+	return nil
+}
+
 // PruneLinks cleans up any Actor Links that can not be resolved in the
 // level data. For example, if actors were linked in Edit Mode and one
 // actor is deleted leaving a broken link.

pkg/level/fmt_readwrite.go

@@ -3,6 +3,7 @@ package level
 import (
 	"fmt"
 	"io/ioutil"
+	"os"
 	"runtime"
 	"strings"
 
@@ -96,7 +97,9 @@ func (m *Level) WriteFile(filename string) error {
 	m.GameVersion = branding.Version
 
 	// Maintenance functions, clean up cruft before save.
-	m.PruneLinks()
+	if err := m.Vacuum(); err != nil {
+		log.Error("Vacuum level %s: %s", filename, err)
+	}
 
 	bin, err := m.ToJSON()
 	if err != nil {
@@ -115,7 +118,7 @@ func (m *Level) WriteFile(filename string) error {
 	}
 
 	// Desktop: write to disk.
-	err = ioutil.WriteFile(filename, bin, 0644)
+	err = os.WriteFile(filename, bin, 0644)
 	if err != nil {
 		return fmt.Errorf("level.WriteFile: %s", err)
 	}

pkg/level/rle/rle.go

@@ -0,0 +1,189 @@
+// Package rle contains support for Run-Length Encoding of level chunks.
+package rle
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"strings"
+
+	"git.kirsle.net/SketchyMaze/doodle/pkg/log"
+	"git.kirsle.net/go/render"
+)
+
+const NullColor = 0xFFFF
+
+// Grid is a 2D array of nullable integers to store a flat bitmap of a chunk.
+type Grid [][]*uint64
+
+// NewGrid will return an initialized 2D grid of equal dimensions of the given size.
+//
+// The grid is indexed in [Y][X] notation, or: by row first and then column.
+func NewGrid(size int) (Grid, error) {
+	if size == 0 {
+		return nil, errors.New("no size given for RLE Grid: the chunker was probably not initialized")
+	}
+
+	var grid = make([][]*uint64, size+1)
+	for i := 0; i < size+1; i++ {
+		grid[i] = make([]*uint64, size+1)
+	}
+
+	return grid, nil
+}
+
+func MustGrid(size int) Grid {
+	grid, err := NewGrid(size)
+	if err != nil {
+		panic(err)
+	}
+	return grid
+}
+
+type Pixel struct {
+	Point   render.Point
+	Palette int
+}
+
+// Size of the grid.
+func (g Grid) Size() int {
+	return len(g[0])
+}
+
+// Compress the grid into a byte stream of RLE compressed data.
+//
+// The compressed format is a stream of:
+//
+// - A Uvarint for the palette index (0-255) or 0xffff (65535) for null.
+// - A Uvarint for how many pixels to repeat that color.
+func (g Grid) Compress() ([]byte, error) {
+	log.Error("BEGIN Compress()")
+	// log.Warn("Visualized:\n%s", g.Visualize())
+
+	// Run-length encode the grid.
+	var (
+		compressed []byte // final result
+		lastColor  uint64 // last color seen (current streak)
+		runLength  uint64 // current streak for the last color
+		buffering  bool   // detect end of grid
+
+		// Flush the buffer
+		flush = func() {
+			// log.Info("flush: %d for %d length", lastColor, runLength)
+			compressed = binary.AppendUvarint(compressed, lastColor)
+			compressed = binary.AppendUvarint(compressed, runLength)
+		}
+	)
+
+	for y, row := range g {
+		for x, nullableIndex := range row {
+			var index uint64
+			if nullableIndex == nil {
+				index = NullColor
+			} else {
+				index = *nullableIndex
+			}
+
+			// First color of the grid
+			if y == 0 && x == 0 {
+				// log.Info("First color @ %dx%d is %d", x, y, index)
+				lastColor = index
+				runLength = 1
+				continue
+			}
+
+			// Buffer it until we get a change of color or EOF.
+			if index != lastColor {
+				// log.Info("Color %d streaks for %d until %dx%d", lastColor, runLength, x, y)
+				flush()
+				lastColor = index
+				runLength = 1
+				buffering = false
+				continue
+			}
+
+			buffering = true
+			runLength++
+		}
+	}
+
+	// Flush the final buffer when we got to EOF on the grid.
+	if buffering {
+		flush()
+	}
+
+	// log.Error("RLE compressed: %v", compressed)
+
+	return compressed, nil
+}
+
+// Decompress the RLE byte stream back into a populated 2D grid.
+func (g Grid) Decompress(compressed []byte) error {
+	log.Error("BEGIN Decompress()")
+	// log.Warn("Visualized:\n%s", g.Visualize())
+
+	// Prepare the 2D grid to decompress the RLE stream into.
+	var (
+		size         = g.Size()
+		x, y, cursor int
+	)
+
+	var reader = bytes.NewBuffer(compressed)
+
+	for {
+		var (
+			paletteIndexRaw, err1 = binary.ReadUvarint(reader)
+			repeatCount, err2     = binary.ReadUvarint(reader)
+		)
+
+		if err1 != nil || err2 != nil {
+			break
+		}
+
+		// Handle the null color.
+		var paletteIndex *uint64
+		if paletteIndexRaw != NullColor {
+			paletteIndex = &paletteIndexRaw
+		}
+
+		// log.Warn("RLE index %v for %dpx", paletteIndexRaw, repeatCount)
+
+		for i := uint64(0); i < repeatCount; i++ {
+			cursor++
+			if cursor%size == 0 {
+				y++
+				x = 0
+			}
+
+			point := render.NewPoint(int(x), int(y))
+			if point.Y >= size || point.X >= size {
+				continue
+			}
+			g[point.Y][point.X] = paletteIndex
+
+			x++
+		}
+	}
+
+	// log.Warn("Visualized:\n%s", g.Visualize())
+
+	return nil
+}
+
+// Visualize the state of the 2D grid.
+func (g Grid) Visualize() string {
+	var lines []string
+	for _, row := range g {
+		var line = "["
+		for _, col := range row {
+			if col == nil {
+				line += " "
+			} else {
+				line += fmt.Sprintf("%x", *col)
+			}
+		}
+		lines = append(lines, line+"]")
+	}
+	return strings.Join(lines, "\n")
+}

pkg/level/rle/rle_test.go

@@ -0,0 +1,43 @@
+package rle_test
+
+import (
+	"testing"
+
+	"git.kirsle.net/SketchyMaze/doodle/pkg/level/rle"
+)
+
+func TestRLE(t *testing.T) {
+
+	// Test a completely filled grid.
+	var (
+		grid  = rle.MustGrid(128)
+		color = uint64(5)
+	)
+	for y := range grid {
+		for x := range y {
+			grid[y][x] = &color
+		}
+	}
+
+	// Compress and decompress it.
+	var (
+		compressed, _ = grid.Compress()
+		grid2         = rle.MustGrid(128)
+	)
+	grid2.Decompress(compressed)
+
+	// Ensure our color is set everywhere.
+	for y := range grid {
+		for x := range y {
+			if grid[y][x] != &color {
+				t.Errorf("RLE compression didn't survive the round trip: %d,%d didn't save\n"+
+					"  Expected: %d\n"+
+					"  Actually: %v",
+					x, y,
+					color,
+					grid[y][x],
+				)
+			}
+		}
+	}
+}

pkg/uix/canvas_editable.go

@@ -420,7 +420,7 @@ func (w *Canvas) loopEditable(ev *event.State) error {
 			baseColor, err := chunker.Get(cursor)
 			if err != nil {
 				limit = balance.FloodToolVoidLimit
-				log.Warn("FloodTool: couldn't get base color at %s: %s (got %s)", cursor, err, baseColor.Color)
+				log.Warn("FloodTool: couldn't get base color at %s: %s (got %+v)", cursor, err, baseColor)
 			}
 
 			// If no change, do nothing.