diff --git a/include/system/graphics.h b/include/system/graphics.h
index 154f9cb..be86ae4 100644
--- a/include/system/graphics.h
+++ b/include/system/graphics.h
@@ -293,6 +293,8 @@
     HAL_TRANSFORM_ROT_180   = 0x03,
     /* rotate source image 270 degrees clockwise */
     HAL_TRANSFORM_ROT_270   = 0x07,
+    /* don't use. see system/window.h */
+    HAL_TRANSFORM_RESERVED  = 0x08,
 };
 
 #ifdef __cplusplus
diff --git a/include/system/window.h b/include/system/window.h
index 7ce59e0..649bd71 100644
--- a/include/system/window.h
+++ b/include/system/window.h
@@ -296,12 +296,15 @@
     NATIVE_WINDOW_TRANSFORM_FLIP_H = HAL_TRANSFORM_FLIP_H ,
     /* flip source image vertically */
     NATIVE_WINDOW_TRANSFORM_FLIP_V = HAL_TRANSFORM_FLIP_V,
-    /* rotate source image 90 degrees clock-wise */
+    /* rotate source image 90 degrees clock-wise, and is applied after TRANSFORM_FLIP_{H|V} */
     NATIVE_WINDOW_TRANSFORM_ROT_90 = HAL_TRANSFORM_ROT_90,
     /* rotate source image 180 degrees */
     NATIVE_WINDOW_TRANSFORM_ROT_180 = HAL_TRANSFORM_ROT_180,
     /* rotate source image 270 degrees clock-wise */
     NATIVE_WINDOW_TRANSFORM_ROT_270 = HAL_TRANSFORM_ROT_270,
+    /* transforms source by the inverse transform of the screen it is displayed onto. This
+     * transform is applied last */
+    NATIVE_WINDOW_TRANSFORM_INVERSE_DISPLAY = 0x08
 };
 
 /* parameter for NATIVE_WINDOW_SET_SCALING_MODE */