packing: Add an extending count at Extend

internal/packing/packing.go

@@ -207,11 +207,14 @@ func walk(n *Node, f func(n *Node) error) error {
 	return nil
 }
 
-func (p *Page) Extend() bool {
+func (p *Page) Extend(count int) bool {
 	if p.size >= p.maxSize {
 		return false
 	}
-	newSize := p.size * 2
+	newSize := p.size
+	for i := 0; i < count; i++ {
+		newSize *= 2
+	}
 	edgeNodes := []*Node{}
 	abort := errors.New("abort")
 	aborted := false

internal/packing/packing_test.go

@@ -257,7 +257,7 @@ func TestExtend(t *testing.T) {
 	p := NewPage(1024, 4096)
 	s := p.Size()
 	p.Alloc(s/2, s/2)
-	p.Extend()
+	p.Extend(1)
 	if p.Size() != s*2 {
 		t.Errorf("p.Size(): got: %d, want: %d", p.Size(), s*2)
 	}
@@ -281,7 +281,7 @@ func TestExtend2(t *testing.T) {
 	p.Alloc(s/2, s/2)
 	p.Free(n1)
 	p.Free(n2)
-	p.Extend()
+	p.Extend(1)
 	if p.Size() != s*2 {
 		t.Errorf("p.Size(): got: %d, want: %d", p.Size(), s*2)
 	}

internal/shareable/image.go

@@ -91,16 +91,17 @@ type backend struct {
 }
 
 func (b *backend) TryAlloc(width, height int) (*packing.Node, bool) {
-	// If the region is allocated without any extension, it's fine.
+	// If the region is allocated without any extension, that's fine.
 	if n := b.page.Alloc(width, height); n != nil {
 		return n, true
 	}
 
 	// Simulate the extending the page and calculate the appropriate page size.
+	// By simulating, we can avoid unnecessary extention of underlying textures.
 	page := b.page.Clone()
 	nExtended := 0
 	for {
-		if !page.Extend() {
+		if !page.Extend(1) {
 			// The page can't be extended any more. Return as failure.
 			return nil, false
 		}
@@ -111,9 +112,7 @@ func (b *backend) TryAlloc(width, height int) (*packing.Node, bool) {
 		}
 	}
 
-	for i := 0; i < nExtended; i++ {
-		b.page.Extend()
-	}
+	b.page.Extend(nExtended)
 	s := b.page.Size()
 	b.restorable = b.restorable.Extend(s, s)