Simplified area coverage calculation a great deal.

common/area.go

@@ -4,7 +4,9 @@
 
 package common
 
-import "math"
+import (
+	"math"
+)
 
 type Area struct {
 	X1, Z1 int16
@@ -28,79 +30,73 @@ func areasContain(areas []Area, x, z int16) bool {
 	return false
 }
 
-// UncoveredAreas implements a greedy algorithm to figure out
+// recalculate implements a greedy algorithm to figure out
 // a list of disjunct areas of free regions in the domain
 // to the (x, z) block plane.
 // oldAreas are searched and found free areas are appended
 // to newAreas which ist return.
 // This is useful to spatial query only blocks from db
 // that are not below already rendered blocks.
-func UncoveredAreas(r *Renderer, newAreas, oldAreas []Area) []Area {
+func (area Area) recalculate(r *Renderer, nareas []Area) []Area {
 	yM := r.yMin
 
-	// Scan old areas.
-	for _, oldArea := range oldAreas {
-		for z := oldArea.Z1; z <= oldArea.Z2; z++ {
-			row := z * int16(r.width)
-			for x := oldArea.X1; x <= oldArea.X2; x++ {
-				// Uncovered and not in list of new areas?
-				if yM[row+x] > math.MinInt32 || areasContain(newAreas, x, z) {
-					continue
-				}
-				area := Area{X1: x, Z1: z, X2: x, Z2: z}
-				// Try to extend the area in x and/or z till no further extension is possible.
-				for extendDirs := 1 | 2; extendDirs != 0; {
-					var xFirst bool
-					// Try to extend in the direction with most gain
-					// of blocks.
-					if area.higher() { // Higher means to win more blocks in x direction.
-						xFirst = true
-					}
-				dirs:
-					for i := 0; i < 2; i++ {
-						if xFirst {
-							// Extension in x possible?
-							if extendDirs&1 == 1 {
-								nx := area.X2 + 1
-								if nx > oldArea.X2 {
-									extendDirs &= ^1
-									continue
-								}
-								// Scan line below current area if its fully free.
-								for nz := area.Z1; nz <= area.Z2; nz++ {
-									if yM[nz*int16(r.width)+nx] > math.MinInt32 || areasContain(newAreas, nx, nz) {
-										extendDirs &= ^1
-										continue dirs
-									}
-								}
-								// free -> extend
-								area.X2 = nx
-							}
-						} else if extendDirs&2 == 2 {
-							// Symmetric case in z direction
-							nz := area.Z2 + 1
-							if nz > oldArea.Z2 {
-								extendDirs &= ^2
-								continue
-							}
-							// Scan line right beside the area if its free.
-							row2 := nz * int16(r.width)
-							for nx := area.X1; nx <= area.X2; nx++ {
-								if yM[row2+nx] > math.MinInt32 || areasContain(newAreas, nx, nz) {
-									extendDirs &= ^2
-									continue dirs
-								}
-							}
-							area.Z2 = nz
-						}
-						// Switch to other search direction (x -> z or z -> x)
-						xFirst = !xFirst
-					}
-				}
-				// At this point the area is extended to max.
-				newAreas = append(newAreas, area)
+	const ex = 1
+	const ez = 2
+
+	nas := len(nareas)
+
+	for z := area.Z1; z <= area.Z2; z++ {
+		row := z * int16(r.width)
+		for x := area.X1; x <= area.X2; x++ {
+			// Uncovered and not in list of new areas?
+			if yM[row+x] > math.MinInt32 || areasContain(nareas[nas:], x, z) {
+				continue
 			}
+			a := Area{X1: x, Z1: z, X2: x, Z2: z}
+			// Try to extend the area in x and/or z till no further extension is possible.
+		ext:
+			for extend := ex | ez; extend != 0; {
+				// If we extending in both directions a the current area
+				// is higher than wide we gain more block if extend
+				// in the x direction first.
+				if (extend == ex|ez && a.higher()) || extend&ex == ex { // check x
+					nx := a.X2 + 1
+					if nx > area.X2 { // reached border of area
+						extend &= ^ex
+						continue
+					}
+					// Check column right of the current area if its fully free.
+					for nz := a.Z1; nz <= a.Z2; nz++ {
+						if yM[nz*int16(r.width)+nx] > math.MinInt32 ||
+							areasContain(nareas[nas:], nx, nz) {
+							extend &= ^ex
+							continue ext
+						}
+					}
+					// free -> extend
+					a.X2 = nx
+				} else if extend&ez == ez { // check z
+					nz := a.Z2 + 1
+					if nz > area.Z2 {
+						extend &= ^ez
+						continue
+					}
+					// Check line right below the current area if its free.
+					row2 := nz * int16(r.width)
+					for nx := a.X1; nx <= a.X2; nx++ {
+						if yM[row2+nx] > math.MinInt32 ||
+							areasContain(nareas[nas:], nx, nz) {
+							extend &= ^ez
+							continue ext
+						}
+					}
+					// free -> extend
+					a.Z2 = nz
+				}
+			}
+			// At this point the area is extended to max.
+			nareas = append(nareas, a)
 		}
 	}
-	return newAreas
+	return nareas
 }

common/basetilecreator.go

@@ -103,10 +103,10 @@ func (btc *BaseTileCreator) CreateTile(x, z int16, i, j int) (bool, error) {
 
 	var c1, c2 Coord
 
-	oareas := make([]Area, 0, tileWidth*tileHeight/2)
-	nareas := make([]Area, 1, tileWidth*tileHeight/2)
+	nareas := make([]Area, 0, tileWidth*tileHeight/2)
+	areas := make([]Area, 1, tileWidth*tileHeight/2)
 
-	nareas[0] = Area{
+	areas[0] = Area{
 		X1: 0, Z1: 0,
 		X2: int16(tileWidth) - 1, Z2: int16(tileHeight) - 1}
 
@@ -118,9 +118,7 @@ func (btc *BaseTileCreator) CreateTile(x, z int16, i, j int) (bool, error) {
 		c1.Y = max16(yRange[0], btc.yMin)
 		c2.Y = min16(yRange[1], btc.yMax)
 
-		var allCount int
-
-		for _, area := range nareas {
+		for _, area := range areas {
 			c1.X = area.X1 + x
 			c1.Z = area.Z1 + z
 			c2.X = area.X2 + x
@@ -131,18 +129,22 @@ func (btc *BaseTileCreator) CreateTile(x, z int16, i, j int) (bool, error) {
 			if count, err = btc.client.QueryCuboid(query, btc.drawBlock); err != nil {
 				return false, err
 			}
-			allCount += count
 			if err = btc.yOrder.Drain(btc.colors); err != nil {
 				log.Printf("WARN: rendering block failed: %s\n", err)
 			}
-		}
-		if allCount > 0 {
-			xareas := UncoveredAreas(btc.renderer, oareas, nareas)
-			if len(xareas) == 0 {
-				break
+
+			// If there where loaded blocks in this area recalculate coverage.
+			if count > 0 {
+				nareas = area.recalculate(btc.renderer, nareas)
+			} else {
+				nareas = append(nareas, area)
 			}
-			nareas, oareas = xareas, nareas[:0]
 		}
+
+		if len(nareas) == 0 {
+			break
+		}
+		areas, nareas = nareas, areas[:0]
 	}
 
 	path := filepath.Join(btc.baseDir, strconv.Itoa(i), strconv.Itoa(j)+".png")