Add ChildrenInZoomRange method

maptile/tile.go

@@ -226,6 +226,34 @@ func (t Tile) Children() Tiles {
 	}
 }
 
+// ChildrenInZoomRange returns all the children tiles of tile from ranges [zoomStart, zoomEnd], both ends inclusive.
+func ChildrenInZoomRange(tile Tile, zoomStart, zoomEnd Zoom) Tiles {
+	if !(zoomStart <= zoomEnd) {
+		panic("zoomStart must be <= zoomEnd")
+	}
+	if !(tile.Z <= zoomStart) {
+		panic("tile.Z is must be <= zoomStart")
+	}
+
+	zDeltaStart := zoomStart - tile.Z
+	zDeltaEnd := zoomEnd - tile.Z
+
+	res := make([]Tile, 0)
+
+	for d := zDeltaStart; d <= zDeltaEnd; d++ {
+		xStart := tile.X << d
+		yStart := tile.Y << d
+		dim := uint32(1 << d)
+		for x := xStart; x < xStart+dim; x++ {
+			for y := yStart; y < yStart+dim; y++ {
+				res = append(res, New(x, y, tile.Z+d))
+			}
+		}
+	}
+
+	return res
+}
+
 // Siblings returns the 4 tiles that share this tile's parent.
 func (t Tile) Siblings() Tiles {
 	return t.Parent().Children()

maptile/tile_test.go

@@ -3,6 +3,7 @@ package maptile
 import (
 	"fmt"
 	"math"
+	"reflect"
 	"testing"
 
 	"github.com/paulmach/orb"
@@ -160,6 +161,98 @@ func TestContains(t *testing.T) {
 	}
 }
 
+func TestChildrenTilesSubRange(t *testing.T) {
+	type args struct {
+		tile      Tile
+		zoomStart Zoom
+		zoomEnd   Zoom
+	}
+	tests := []struct {
+		name string
+		args args
+		want Tiles
+	}{
+		{
+			name: "self zoom",
+			args: args{
+				tile:      New(0, 0, 0),
+				zoomStart: 0,
+				zoomEnd:   0,
+			},
+			want: Tiles{New(0, 0, 0)},
+		},
+		{
+			name: "1 level zooming including zoom 0",
+			args: args{
+				tile:      New(0, 0, 0),
+				zoomStart: 0,
+				zoomEnd:   1,
+			},
+			want: Tiles{New(0, 0, 0), New(0, 0, 1), New(0, 1, 1), New(1, 0, 1), New(1, 1, 1)},
+		},
+		{
+			name: "1 level zooming excluding zoom 0",
+			args: args{
+				tile:      New(0, 0, 0),
+				zoomStart: 1,
+				zoomEnd:   1,
+			},
+			want: Tiles{New(0, 0, 1), New(0, 1, 1), New(1, 0, 1), New(1, 1, 1)},
+		},
+		{
+			name: "2 level zooming",
+			args: args{
+				tile:      New(0, 0, 0),
+				zoomStart: 2,
+				zoomEnd:   2,
+			},
+			want: Tiles{
+				New(0, 0, 2),
+				New(0, 1, 2),
+				New(0, 2, 2),
+				New(0, 3, 2),
+				New(1, 0, 2),
+				New(1, 1, 2),
+				New(1, 2, 2),
+				New(1, 3, 2),
+				New(2, 0, 2),
+				New(2, 1, 2),
+				New(2, 2, 2),
+				New(2, 3, 2),
+				New(3, 0, 2),
+				New(3, 1, 2),
+				New(3, 2, 2),
+				New(3, 3, 2),
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if !reflect.DeepEqual(tt.want, ChildrenInZoomRange(tt.args.tile, tt.args.zoomStart, tt.args.zoomEnd)) {
+				t.Errorf("tiles not equal")
+			}
+		})
+	}
+}
+
+func TestChildrenTilesSubRangeInvalidParams_ZoomStart_Larger_Than_ZoomEnd(t *testing.T) {
+	// No need to check whether `recover()` is nil. Just turn off the panic.
+	defer func() { _ = recover() }()
+	tile := New(0, 0, 0)
+	ChildrenInZoomRange(tile, 10, 8)
+	// Never reaches here if `ChildrenInZoomRange` panics.
+	t.Errorf("did not panic")
+}
+
+func TestChildrenTilesSubRangeInvalidParams_TileZ_Larger_Than_ZoomStart(t *testing.T) {
+	// No need to check whether `recover()` is nil. Just turn off the panic.
+	defer func() { _ = recover() }()
+	tile := New(0, 0, 10)
+	ChildrenInZoomRange(tile, 9, 12)
+	// Never reaches here if `ChildrenInZoomRange` panics.
+	t.Errorf("did not panic")
+}
+
 func TestRange(t *testing.T) {
 	tile := New(4, 4, 5)
 	min, max := tile.Range(3)