diff --git a/cmd/tilemapper/main.go b/cmd/tilemapper/main.go
index 227a807..fd977fa 100644
--- a/cmd/tilemapper/main.go
+++ b/cmd/tilemapper/main.go
@@ -70,7 +70,8 @@ func main() {
 	q1x, q1y, q1z := int16(x), int16(y), int16(z)
 	q2x, q2y, q2z := q1x+int16(width)-1, q1y+int16(depth)-1, q1z+int16(height)-1
 
-	renderer := common.NewRenderer(q1x, q1z, width, height)
+	renderer := common.NewRenderer(width, height)
+	renderer.SetPos(q1x, q1z)
 	yOrder := common.NewYOrder(renderer, 512)
 
 	numBlocks := 0
diff --git a/common/renderer.go b/common/renderer.go
index c60473e..34e9a68 100644
--- a/common/renderer.go
+++ b/common/renderer.go
@@ -40,6 +40,10 @@ func NewYOrder(renderer *Renderer, capacity int) *YOrder {
 		capacity: capacity}
 }
 
+func (yo *YOrder) Reset() {
+	yo.blocks = yo.blocks[0:0]
+}
+
 func max(a, b int) int {
 	if a > b {
 		return a
@@ -116,33 +120,39 @@ func (yo *YOrder) Pop() (x interface{}) {
 	return x
 }
 
-func NewRenderer(xOfs, zOfs int16, width, height int) (renderer *Renderer) {
+func NewRenderer(width, height int) (renderer *Renderer) {
 	dim := width * height
 	pixSize := dim * 16 * 16
 	yBuffer := make([]int32, pixSize)
 	cBuffer := make([]int32, pixSize)
 	yMin := make([]int32, dim)
 
-	for i := 0; i < pixSize; i++ {
-		yBuffer[i] = math.MinInt32
-		cBuffer[i] = -1
-	}
-
-	for i := 0; i < dim; i++ {
-		yMin[i] = math.MinInt32
-	}
-
 	renderer = &Renderer{
 		width:   width,
 		height:  height,
-		xOfs:    xOfs,
-		zOfs:    zOfs,
 		yBuffer: yBuffer,
 		cBuffer: cBuffer,
 		yMin:    yMin}
+
+	renderer.Reset()
 	return
 }
 
+func (r *Renderer) SetPos(xOfs, zOfs int16) {
+	r.xOfs = xOfs
+	r.zOfs = zOfs
+}
+
+func (r *Renderer) Reset() {
+	for i, n := 0, len(r.yBuffer); i < n; i++ {
+		r.yBuffer[i] = math.MinInt32
+		r.cBuffer[i] = -1
+	}
+	for i, n := 0, len(r.yMin); i < n; i++ {
+		r.yMin[i] = math.MinInt32
+	}
+}
+
 func (r *Renderer) IsFilled() bool {
 	for _, y := range r.yMin {
 		if y == math.MinInt32 {