diff --git a/libs/ui/DebugUtils.cpp b/libs/ui/DebugUtils.cpp
index f394635..1f006ce 100644
--- a/libs/ui/DebugUtils.cpp
+++ b/libs/ui/DebugUtils.cpp
@@ -321,10 +321,6 @@
     return std::string("Unknown RenderIntent");
 }
 
-std::string to_string(const android::Rect& rect) {
-    return StringPrintf("(%4d,%4d,%4d,%4d)", rect.left, rect.top, rect.right, rect.bottom);
-}
-
 std::string toString(const android::DeviceProductInfo::ManufactureOrModelDate& date) {
     using ModelYear = android::DeviceProductInfo::ModelYear;
     using ManufactureYear = android::DeviceProductInfo::ManufactureYear;
diff --git a/libs/ui/Rect.cpp b/libs/ui/Rect.cpp
index 13fed3a..a8d6285 100644
--- a/libs/ui/Rect.cpp
+++ b/libs/ui/Rect.cpp
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include <android-base/stringprintf.h>
 #include <system/graphics.h>
 #include <ui/Rect.h>
 
@@ -149,4 +150,13 @@
     return result;
 }
 
+std::string to_string(const android::Rect& rect) {
+    return android::base::StringPrintf("Rect(%d, %d, %d, %d)", rect.left, rect.top, rect.right,
+                                       rect.bottom);
+}
+
+void PrintTo(const Rect& rect, ::std::ostream* os) {
+    *os << to_string(rect);
+}
+
 }; // namespace android
diff --git a/libs/ui/include/ui/DebugUtils.h b/libs/ui/include/ui/DebugUtils.h
index 4685575..18cd487 100644
--- a/libs/ui/include/ui/DebugUtils.h
+++ b/libs/ui/include/ui/DebugUtils.h
@@ -34,5 +34,4 @@
 std::string decodeColorTransform(android_color_transform colorTransform);
 std::string decodePixelFormat(android::PixelFormat format);
 std::string decodeRenderIntent(android::ui::RenderIntent renderIntent);
-std::string to_string(const android::Rect& rect);
 std::string toString(const android::DeviceProductInfo&);
diff --git a/libs/ui/include/ui/DisplayState.h b/libs/ui/include/ui/DisplayState.h
index 64efc84..70a0d50 100644
--- a/libs/ui/include/ui/DisplayState.h
+++ b/libs/ui/include/ui/DisplayState.h
@@ -32,7 +32,7 @@
 struct DisplayState {
     LayerStack layerStack = NO_LAYER_STACK;
     Rotation orientation = ROTATION_0;
-    Size viewport;
+    Size layerStackSpaceRect;
 };
 
 static_assert(std::is_trivially_copyable_v<DisplayState>);
diff --git a/libs/ui/include/ui/Rect.h b/libs/ui/include/ui/Rect.h
index 2f2229e..6670dc0 100644
--- a/libs/ui/include/ui/Rect.h
+++ b/libs/ui/include/ui/Rect.h
@@ -19,10 +19,10 @@
 
 #include <ostream>
 
+#include <log/log.h>
 #include <utils/Flattenable.h>
 #include <utils/Log.h>
 #include <utils/TypeHelpers.h>
-#include <log/log.h>
 
 #include <ui/FloatRect.h>
 #include <ui/Point.h>
@@ -216,11 +216,10 @@
     }
 };
 
+std::string to_string(const android::Rect& rect);
+
 // Defining PrintTo helps with Google Tests.
-static inline void PrintTo(const Rect& rect, ::std::ostream* os) {
-    *os << "Rect(" << rect.left << ", " << rect.top << ", " << rect.right << ", " << rect.bottom
-        << ")";
-}
+void PrintTo(const Rect& rect, ::std::ostream* os);
 
 ANDROID_BASIC_TYPES_TRAITS(Rect)
 
diff --git a/libs/ui/include/ui/Rotation.h b/libs/ui/include/ui/Rotation.h
index 89008f6..83d431d 100644
--- a/libs/ui/include/ui/Rotation.h
+++ b/libs/ui/include/ui/Rotation.h
@@ -41,6 +41,15 @@
     return toRotation((toRotationInt(lhs) + toRotationInt(rhs)) % N);
 }
 
+constexpr Rotation operator-(Rotation lhs, Rotation rhs) {
+    constexpr auto N = toRotationInt(ROTATION_270) + 1;
+    return toRotation((N + toRotationInt(lhs) - toRotationInt(rhs)) % N);
+}
+
+constexpr Rotation operator-(Rotation rotation) {
+    return ROTATION_0 - rotation;
+}
+
 constexpr const char* toCString(Rotation rotation) {
     switch (rotation) {
         case ROTATION_0: