Merged the supress-identical-tile-overwrite feature branch.

The webmapper now has an internal cache of SHA1 hashes of the last 256 base tiles it writes to disk.
If a tile is regenerated its hash is compared to the already stored.
If the hash is the same as the one before the tile is not stored to file
and the pyramid tiles are not updated, too.

cmd/mtseeder/baselevel.go

@@ -68,7 +68,7 @@ func createBaseLevel(
 		btc := common.NewBaseTileCreator(
 			client, colors, bg,
 			int16(yMin), int16(yMax),
-			transparent, baseDir, false)
+			transparent, baseDir, nil)
 		go createTiles(btc, jobs, &done)
 	}
 

cmd/mtwebmapper/forwardupdates.go

@@ -27,7 +27,7 @@ type connection struct {
 }
 
 type msg struct {
-	tiles map[xz]bool
+	tiles []xz
 	pls   []*player
 }
 
@@ -57,12 +57,8 @@ func (wsf *websocketForwarder) run() {
 			}
 			encMsg := map[string]interface{}{}
 
-			if tiles := message.tiles; tiles != nil {
-				xzs := make([]xz, 0, len(tiles))
-				for xz := range tiles {
-					xzs = append(xzs, xz)
-				}
-				encMsg["tiles"] = xzs
+			if message.tiles != nil {
+				encMsg["tiles"] = message.tiles
 			}
 
 			if message.pls != nil {
@@ -101,7 +97,7 @@ func (wsf *websocketForwarder) ServeHTTP(rw http.ResponseWriter, r *http.Request
 	c.reader()
 }
 
-func (wsf *websocketForwarder) BaseTilesUpdated(changes map[xz]bool) {
+func (wsf *websocketForwarder) BaseTilesUpdated(changes []xz) {
 	wsf.broadcast <- msg{tiles: changes}
 }
 

cmd/mtwebmapper/tilesupdater.go

@@ -24,12 +24,15 @@ import (
 	"bitbucket.org/s_l_teichmann/mtsatellite/common"
 )
 
+// Number of check sums to keep in memory.
+const maxHashedTiles = 256
+
 type baseTilesUpdates interface {
-	BaseTilesUpdated(map[xz]bool)
+	BaseTilesUpdated([]xz)
 }
 
 type tileUpdater struct {
-	changes      map[xz]bool
+	changes      map[xz]struct{}
 	btu          baseTilesUpdates
 	mapDir       string
 	redisAddress string
@@ -48,8 +51,13 @@ type xz struct {
 	Z int16
 }
 
+type xzc struct {
+	xz
+	canceled bool
+}
+
 type xzm struct {
-	P    xz
+	xz
 	Mask uint16
 }
 
@@ -65,8 +73,8 @@ func (c xz) parent() xzm {
 	xp, xr := c.X>>1, uint16(c.X&1)
 	zp, zr := c.Z>>1, uint16(c.Z&1)
 	return xzm{
-		P:    xz{X: xp, Z: zp},
-		Mask: 1 << (zr<<1 | xr)}
+		xz{X: xp, Z: zp},
+		1 << (zr<<1 | xr)}
 }
 
 func newTileUpdater(
@@ -84,7 +92,7 @@ func newTileUpdater(
 		mapDir:       mapDir,
 		redisAddress: redisAddress,
 		ips:          ips,
-		changes:      map[xz]bool{},
+		changes:      map[xz]struct{}{},
 		colors:       colors,
 		bg:           bg,
 		yMin:         int16(yMin),
@@ -141,7 +149,7 @@ func (tu *tileUpdater) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
 	if len(newChanges) > 0 {
 		tu.cond.L.Lock()
 		for _, c := range newChanges {
-			tu.changes[c.quantize()] = true
+			tu.changes[c.quantize()] = struct{}{}
 		}
 		tu.cond.L.Unlock()
 		tu.cond.Signal()
@@ -150,21 +158,42 @@ func (tu *tileUpdater) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
 	rw.WriteHeader(http.StatusOK)
 }
 
+func extractChanges(changes map[xz]struct{}) []xzc {
+	chs := make([]xzc, len(changes))
+	var i int
+	for ch := range changes {
+		chs[i] = xzc{ch, false}
+		i++
+	}
+	return chs
+}
+
+func activeChanges(changes []xzc) []xz {
+	chs := make([]xz, 0, len(changes))
+	for i := range changes {
+		if !changes[i].canceled {
+			chs = append(chs, changes[i].xz)
+		}
+	}
+	return chs
+}
+
 func (tu *tileUpdater) doUpdates() {
 
+	bth := common.NewBaseTileHash(maxHashedTiles)
+
+	baseDir := filepath.Join(tu.mapDir, "8")
+
 	for {
-		var changes map[xz]bool
 		tu.cond.L.Lock()
 		for len(tu.changes) == 0 {
 			tu.cond.Wait()
 		}
-		changes = tu.changes
-		tu.changes = map[xz]bool{}
+		changes := extractChanges(tu.changes)
+		tu.changes = map[xz]struct{}{}
 		tu.cond.L.Unlock()
 
-		baseDir := filepath.Join(tu.mapDir, "8")
-
-		jobs := make(chan xz)
+		jobs := make(chan *xzc)
 		var done sync.WaitGroup
 
 		for i, n := 0, common.Min(tu.workers, len(changes)); i < n; i++ {
@@ -177,22 +206,29 @@ func (tu *tileUpdater) doUpdates() {
 			btc := common.NewBaseTileCreator(
 				client, tu.colors, tu.bg,
 				tu.yMin, tu.yMax,
-				tu.transparent, baseDir, true)
+				tu.transparent, baseDir, bth.Update)
 			done.Add(1)
 			go tu.updateBaseTiles(jobs, btc, &done)
 		}
 
-		parentJobs := make(map[xz]uint16)
-
-		for c := range changes {
-			//log.Printf("job: %+v\n", c)
-			jobs <- c
-			pxz := c.parent()
-			parentJobs[pxz.P] |= pxz.Mask
+		for i := range changes {
+			jobs <- &changes[i]
 		}
 		close(jobs)
 		done.Wait()
 
+		actChs := activeChanges(changes)
+
+		if len(actChs) == 0 {
+			continue
+		}
+
+		parentJobs := make(map[xz]uint16)
+		for i := range actChs {
+			pxz := actChs[i].parent()
+			parentJobs[pxz.xz] |= pxz.Mask
+		}
+
 		for level := 7; level >= 0; level-- {
 			pJobs := make(chan xzm)
 			for i, n := 0, common.Min(len(parentJobs), tu.workers); i < n; i++ {
@@ -201,9 +237,9 @@ func (tu *tileUpdater) doUpdates() {
 			}
 			ppJobs := make(map[xz]uint16)
 			for c, mask := range parentJobs {
-				pJobs <- xzm{P: c, Mask: mask}
+				pJobs <- xzm{c, mask}
 				pxz := c.parent()
-				ppJobs[pxz.P] |= pxz.Mask
+				ppJobs[pxz.xz] |= pxz.Mask
 			}
 			close(pJobs)
 			done.Wait()
@@ -211,7 +247,7 @@ func (tu *tileUpdater) doUpdates() {
 		}
 
 		if tu.btu != nil {
-			tu.btu.BaseTilesUpdated(changes)
+			tu.btu.BaseTilesUpdated(actChs)
 		}
 	}
 }
@@ -257,8 +293,8 @@ func (tu *tileUpdater) updatePyramidTile(scratch, resized *image.RGBA, level int
 	origPath := filepath.Join(
 		tu.mapDir,
 		strconv.Itoa(level),
-		strconv.Itoa(int(j.P.X)),
-		strconv.Itoa(int(j.P.Z))+".png")
+		strconv.Itoa(int(j.X)),
+		strconv.Itoa(int(j.Z))+".png")
 
 	sr := resized.Bounds()
 	levelDir := strconv.Itoa(level + 1)
@@ -266,7 +302,7 @@ func (tu *tileUpdater) updatePyramidTile(scratch, resized *image.RGBA, level int
 		if j.Mask&(1<<i) != 0 {
 			//log.Printf("level %d: modified %d\n", level, i)
 			o := ofs[i]
-			bx, bz := int(2*j.P.X), int(2*j.P.Z)
+			bx, bz := int(2*j.X), int(2*j.Z)
 			path := filepath.Join(
 				tu.mapDir,
 				levelDir,
@@ -294,7 +330,7 @@ func (tu *tileUpdater) updatePyramidTile(scratch, resized *image.RGBA, level int
 }
 
 func (tu *tileUpdater) updateBaseTiles(
-	jobs chan xz,
+	jobs chan *xzc,
 	btc *common.BaseTileCreator, done *sync.WaitGroup) {
 
 	defer btc.Close()
@@ -302,8 +338,12 @@ func (tu *tileUpdater) updateBaseTiles(
 	for job := range jobs {
 		xz := job.dequantize()
 		//log.Printf("%d/%d %d/%d", x, z, job.X, job.Z)
-		if err := btc.CreateTile(xz.X-1, xz.Z-1, int(job.X), int(job.Z)); err != nil {
+		updated, err := btc.CreateTile(xz.X-1, xz.Z-1, int(job.X), int(job.Z))
+		if err != nil {
 			log.Printf("WARN: create tile failed: %s\n", err)
 		}
+		if !updated {
+			job.canceled = true
+		}
 	}
 }

common/basetilecreator.go

@@ -49,6 +49,8 @@ var tileDepths = [...][2]int16{
 
 var BackgroundColor = color.RGBA{R: 0xff, G: 0xff, B: 0xff, A: 0xff}
 
+type BaseTileUpdateFunc func(x, y int, hash []byte) bool
+
 type BaseTileCreator struct {
 	client     *RedisClient
 	colors     *Colors
@@ -57,7 +59,7 @@ type BaseTileCreator struct {
 	yMin       int16
 	yMax       int16
 	baseDir    string
-	update     bool
+	update     BaseTileUpdateFunc
 	emptyImage []byte
 	bg         color.RGBA
 }
@@ -69,7 +71,7 @@ func NewBaseTileCreator(
 	yMin, yMax int16,
 	transparent bool,
 	baseDir string,
-	update bool) *BaseTileCreator {
+	update BaseTileUpdateFunc) *BaseTileCreator {
 	renderer := NewRenderer(tileWidth, tileHeight, transparent)
 	yMin, yMax = Order16(yMin, yMax)
 	return &BaseTileCreator{
@@ -88,7 +90,7 @@ func (btc *BaseTileCreator) Close() error {
 	return btc.client.Close()
 }
 
-func (btc *BaseTileCreator) CreateTile(x, z int16, i, j int) error {
+func (btc *BaseTileCreator) CreateTile(x, z int16, i, j int) (bool, error) {
 	btc.renderer.Reset()
 	btc.renderer.SetPos(x, z)
 	btc.yOrder.Reset()
@@ -128,7 +130,7 @@ func (btc *BaseTileCreator) CreateTile(x, z int16, i, j int) error {
 			c2.Z = area.Z2 + z
 			query := Cuboid{P1: c1, P2: c2}
 			if err := btc.client.QueryCuboid(query, drawBlock); err != nil {
-				return err
+				return false, err
 			}
 			if err := btc.yOrder.Drain(btc.colors); err != nil {
 				log.Printf("WARN: rendering block failed: %s\n", err)
@@ -140,28 +142,34 @@ func (btc *BaseTileCreator) CreateTile(x, z int16, i, j int) error {
 	path := filepath.Join(btc.baseDir, strconv.Itoa(i), strconv.Itoa(j)+".png")
 
 	// Empty images are likely to be produced during seeding.
-	if !btc.update && btc.renderer.IsEmpty() {
+	if btc.update == nil && btc.renderer.IsEmpty() {
 		// To avoid redundant encoding cache the resulting empty image.
 		if btc.emptyImage == nil {
 			var err error
 			m := BackgroundImage((tileWidth-2)*16, (tileHeight-2)*16, btc.bg)
 			if btc.emptyImage, err = EncodeToMem(m); err != nil {
-				return err
+				return false, err
 			}
 		}
 		//log.Printf("Writing empty (%d, %d) to file %s\n", x, z, path)
-		return ioutil.WriteFile(path, btc.emptyImage, 0666)
+		return true, ioutil.WriteFile(path, btc.emptyImage, 0666)
 	}
 
 	image := btc.renderer.CreateShadedImage(
 		16, 16, (tileWidth-2)*16, (tileHeight-2)*16,
 		btc.colors, btc.bg)
 
-	log.Printf("Writing (%d, %d) to file %s\n", x, z, path)
-
-	if !btc.update {
-		return SaveAsPNG(path, image)
+	if btc.update == nil {
+		log.Printf("Writing (%d, %d) to file %s.\n", x, z, path)
+		return true, SaveAsPNG(path, image)
 	}
 
-	return SaveAsPNGAtomic(path, image)
+	if btc.update(i, j, SHA1Image(image)) {
+		log.Printf("Writing (%d, %d) to file %s.\n", x, z, path)
+		return true, SaveAsPNGAtomic(path, image)
+	}
+
+	log.Printf("(%d, %d) is unchanged.\n", x, z)
+
+	return false, nil
 }

common/basetilehash.go

@@ -0,0 +1,92 @@
+// Copyright 2016 by Sascha L. Teichmann
+// Use of this source code is governed by the MIT license
+// that can be found in the LICENSE file.
+
+package common
+
+import (
+	"bytes"
+	"sync"
+)
+
+type btKey struct {
+	x int
+	y int
+}
+
+type btHashEntry struct {
+	prev *btHashEntry
+	next *btHashEntry
+	hash []byte
+	btKey
+}
+
+type BaseTileHash struct {
+	hashes     map[btKey]*btHashEntry
+	maxEntries int
+	root       btHashEntry
+	sync.Mutex
+}
+
+func NewBaseTileHash(maxEntries int) *BaseTileHash {
+	bth := &BaseTileHash{
+		hashes:     map[btKey]*btHashEntry{},
+		maxEntries: maxEntries}
+	bth.root.next = &bth.root
+	bth.root.prev = &bth.root
+	return bth
+}
+
+func (bth *BaseTileHash) toFront(entry *btHashEntry) {
+	if bth.root.next == entry {
+		return
+	}
+	entry.prev.next = entry.next
+	entry.next.prev = entry.prev
+
+	entry.next = bth.root.next
+	entry.prev = &bth.root
+
+	bth.root.next.prev = entry
+	bth.root.next = entry
+}
+
+func (bth *BaseTileHash) removeLast() *btHashEntry {
+	last := bth.root.prev
+	bth.root.prev = last.prev
+	last.prev.next = &bth.root
+	delete(bth.hashes, last.btKey)
+	return last
+}
+
+func (bth *BaseTileHash) insertFront(entry *btHashEntry) {
+	entry.next = bth.root.next
+	entry.prev = &bth.root
+	bth.root.next.prev = entry
+	bth.root.next = entry
+}
+
+func (bth *BaseTileHash) Update(x, y int, hash []byte) bool {
+	bth.Lock()
+	defer bth.Unlock()
+	key := btKey{x, y}
+	if old, found := bth.hashes[key]; found {
+		if !bytes.Equal(old.hash, hash) {
+			old.hash = hash
+			bth.toFront(old)
+			return true
+		}
+		return false
+	}
+	var entry *btHashEntry
+	if len(bth.hashes) >= bth.maxEntries {
+		entry = bth.removeLast()
+	} else {
+		entry = new(btHashEntry)
+	}
+	entry.btKey = key
+	entry.hash = hash
+	bth.hashes[key] = entry
+	bth.insertFront(entry)
+	return true
+}

common/basetilehash_test.go

@@ -0,0 +1,147 @@
+// Copyright 2016 by Sascha L. Teichmann
+// Use of this source code is governed by the MIT license
+// that can be found in the LICENSE file.
+
+package common
+
+import (
+	"math/rand"
+	"testing"
+)
+
+func randomBaseTileHash(updates int) *BaseTileHash {
+	bth := NewBaseTileHash(256)
+	h1 := []byte{1}
+	h2 := []byte{2}
+	for i := 0; i < updates; i++ {
+		x, y := rand.Intn(100), rand.Intn(100)
+		var h []byte
+		if i%2 == 0 {
+			h = h1
+		} else {
+			h = h2
+		}
+		bth.Update(x, y, h)
+	}
+	return bth
+}
+
+func TestBaseTileHashLenList(t *testing.T) {
+	for _, updates := range []int{53, 111, 1345, 11261} {
+		bth := randomBaseTileHash(updates)
+		countNext := 0
+		for cur := bth.root.next; cur != &bth.root; cur = cur.next {
+			countNext++
+		}
+		countPrev := 0
+		for cur := bth.root.prev; cur != &bth.root; cur = cur.prev {
+			countPrev++
+		}
+		if countPrev != countNext {
+			t.Errorf("count prev != count next: %d %d", countPrev, countNext)
+		}
+		if countPrev != len(bth.hashes) {
+			t.Errorf("count prev != len(hash): %d %d", countPrev, len(bth.hashes))
+		}
+	}
+}
+
+func TestBaseTileHashIntegrity(t *testing.T) {
+	for _, updates := range []int{10, 100, 1000, 10000} {
+		bth := randomBaseTileHash(updates)
+		entries := map[*btHashEntry]bool{}
+
+		for cur := bth.root.next; cur != &bth.root; cur = cur.next {
+			if entries[cur] {
+				t.Errorf("hash element found more than once: %d", updates)
+			}
+			entries[cur] = true
+		}
+		if len(entries) != len(bth.hashes) {
+			t.Errorf("List has differnt length than hashes: %d : %d",
+				len(entries), len(bth.hashes))
+		}
+		var already1 bool
+		var already2 bool
+		for k, v := range bth.hashes {
+			if !entries[v] {
+				if !already1 {
+					already1 = true
+					t.Errorf("Hash contains pointer to element not being in list: %d",
+						updates)
+				}
+			}
+			if k != v.btKey {
+				if !already2 {
+					already2 = true
+					t.Errorf("Key in entry does not match hash key: %d", updates)
+				}
+			}
+			delete(entries, v)
+		}
+
+		if len(entries) > 0 {
+			t.Error("There are more entries than indexed by hash")
+		}
+	}
+}
+
+func TestBaseTileHashOverwrite(t *testing.T) {
+	bth := NewBaseTileHash(256)
+	h1 := []byte{1}
+	h2 := []byte{2}
+
+	if updated := bth.Update(0, 0, h1); !updated {
+		t.Error("First insert does not trigger update")
+	}
+
+	if updated := bth.Update(0, 0, h2); !updated {
+		t.Error("Second insert does not trigger update")
+	}
+
+	if updated := bth.Update(0, 0, h2); updated {
+		t.Error("Third insert does trigger update")
+	}
+}
+
+func TestBaseTileHashSeparate(t *testing.T) {
+	bth := NewBaseTileHash(256)
+	h1 := []byte{1}
+
+	if updated := bth.Update(0, 0, h1); !updated {
+		t.Error("First insert does not trigger update")
+	}
+
+	if updated := bth.Update(0, 1, h1); !updated {
+		t.Error("Second insert does not trigger update")
+	}
+
+	if updated := bth.Update(1, 0, h1); !updated {
+		t.Error("Third insert does trigger update")
+	}
+
+	if len(bth.hashes) != 3 {
+		t.Errorf("Expected size to be 3. Current size: %d", len(bth.hashes))
+	}
+}
+
+func TestBaseTileHashLRU(t *testing.T) {
+	bth := NewBaseTileHash(2)
+	h1 := []byte{1}
+
+	if updated := bth.Update(0, 0, h1); !updated {
+		t.Error("First insert does not trigger update")
+	}
+
+	if updated := bth.Update(0, 1, h1); !updated {
+		t.Error("Second insert does not trigger update")
+	}
+
+	if updated := bth.Update(1, 0, h1); !updated {
+		t.Error("Third insert does trigger update")
+	}
+
+	if len(bth.hashes) != 2 {
+		t.Errorf("Expected size to be 2. Current size: %d", len(bth.hashes))
+	}
+}

common/image.go

@@ -7,6 +7,7 @@ package common
 import (
 	"bufio"
 	"bytes"
+	"crypto/sha1"
 	"errors"
 	"image"
 	"image/color"
@@ -44,7 +45,7 @@ func nextSuffix() string {
 
 func EncodeToMem(img image.Image) ([]byte, error) {
 	var buf bytes.Buffer
-	enc := png.Encoder{png.BestCompression}
+	enc := png.Encoder{CompressionLevel: png.BestCompression}
 	if err := enc.Encode(&buf, img); err != nil {
 		return nil, err
 	}
@@ -110,3 +111,17 @@ func LoadPNG(path string, bg color.RGBA) image.Image {
 	}
 	return img
 }
+
+func SHA1Image(img *image.RGBA) []byte {
+
+	hash := sha1.New()
+	w, h := img.Rect.Dx()*4, img.Rect.Dy()
+
+	pos := img.PixOffset(img.Rect.Min.X, img.Rect.Min.Y)
+
+	for ; h > 0; h, pos = h-1, pos+img.Stride {
+		hash.Write(img.Pix[pos : pos+w])
+	}
+
+	return hash.Sum(nil)
+}