Some little experiment with a coverage index to speed up spatial queries if backend has no Z order support.

common/coords.go

@@ -45,20 +45,6 @@ func (c Coord) String() string {
 	return fmt.Sprintf("(%d, %d, %d)", c.X, c.Y, c.Z)
 }
 
-func minComponent(a, b int16) int16 {
-	if a < b {
-		return a
-	}
-	return b
-}
-
-func maxComponent(a, b int16) int16 {
-	if a > b {
-		return a
-	}
-	return b
-}
-
 func clipComponent(x int16) int16 {
 	if x < minValue {
 		return minValue
@@ -78,16 +64,16 @@ func ClipCoord(c Coord) Coord {
 
 func MinCoord(a, b Coord) Coord {
 	return Coord{
-		X: minComponent(a.X, b.X),
-		Y: minComponent(a.Y, b.Y),
-		Z: minComponent(a.Z, b.Z)}
+		X: min16(a.X, b.X),
+		Y: min16(a.Y, b.Y),
+		Z: min16(a.Z, b.Z)}
 }
 
 func MaxCoord(a, b Coord) Coord {
 	return Coord{
-		X: maxComponent(a.X, b.X),
-		Y: maxComponent(a.Y, b.Y),
-		Z: maxComponent(a.Z, b.Z)}
+		X: max16(a.X, b.X),
+		Y: max16(a.Y, b.Y),
+		Z: max16(a.Z, b.Z)}
 }
 
 // DecodeStringFromBytes constructs a database key out of byte slice.

common/coverage.go

@@ -0,0 +1,82 @@
+package common
+
+import "sync"
+
+type zRange struct {
+	y1     int16
+	y2     int16
+	xRange *Span
+}
+
+type Coverage3D struct {
+	pool    *SpanPool
+	zRanges map[int16]*zRange
+	mu      sync.RWMutex
+}
+
+type Range struct {
+	Z  int16
+	Y1 int16
+	Y2 int16
+	X1 int16
+	X2 int16
+}
+
+func NewCoverage3D() *Coverage3D {
+	return &Coverage3D{
+		pool:    NewSpanPool(),
+		zRanges: map[int16]*zRange{}}
+}
+
+func (s2d *Coverage3D) Insert(c Coord) {
+	s2d.mu.Lock()
+	defer s2d.mu.Unlock()
+	zr := s2d.zRanges[c.Z]
+	if zr == nil {
+		xr := s2d.pool.Alloc()
+		xr.From = int32(c.X)
+		xr.To = int32(c.X)
+		xr.Next = nil
+		s2d.zRanges[c.Z] = &zRange{
+			y1:     c.Y,
+			y2:     c.Y,
+			xRange: xr}
+		return
+	}
+	zr.xRange = s2d.pool.Insert(zr.xRange, int32(c.X), 0)
+	if c.Y < zr.y1 {
+		zr.y1 = c.Y
+	}
+	if c.Y > zr.y2 {
+		zr.y2 = c.Y
+	}
+}
+
+func (s2d *Coverage3D) Query(c1, c2 Coord) []Range {
+
+	c1, c2 = MinCoord(c1, c2), MaxCoord(c1, c2)
+
+	s2d.mu.RLock()
+	defer s2d.mu.RUnlock()
+
+	r := make([]Range, 0, 32)
+	for z := c1.Z; z <= c2.Z; z++ {
+		zr := s2d.zRanges[z]
+		if zr == nil || c1.Y > zr.y2 || c2.Y < zr.y1 {
+			continue
+		}
+		y1, y2 := max16(c1.Y, zr.y1), min16(c2.Y, zr.y2)
+		for xr := zr.xRange; xr != nil && xr.From <= int32(c2.X); xr = xr.Next {
+			if xr.To < int32(c1.X) {
+				continue
+			}
+			r = append(r, Range{
+				Z:  z,
+				Y1: y1,
+				Y2: y2,
+				X1: max16(c1.X, int16(xr.From)),
+				X2: min16(c2.X, int16(xr.To))})
+		}
+	}
+	return r
+}

common/math.go

@@ -0,0 +1,36 @@
+package common
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func max32(a, b int32) int32 {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func min32(a, b int32) int32 {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+func max16(a, b int16) int16 {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func min16(a, b int16) int16 {
+	if a < b {
+		return a
+	}
+	return b
+}

common/renderer.go

@@ -48,20 +48,6 @@ func (yo *YOrder) Reset() {
 	yo.blocks = yo.blocks[0:0]
 }
 
-func max(a, b int) int {
-	if a > b {
-		return a
-	}
-	return b
-}
-
-func max32(a, b int32) int32 {
-	if a > b {
-		return a
-	}
-	return b
-}
-
 func copyData(data []byte) []byte {
 	l := len(data)
 	ndata := make([]byte, l, max(l, 8*1024))