Dirty rect must expand, not contract.

Different devices have different precision, leading to different pixels
being touched during rendering operations. We need to ensure that the
dirty rect we draw with (and which gets erased on the following frame)
encompasses all possible pixels instead of some ideal rounded rectangle.

The bug from this code led to dropped-pixels artifacts on some devices,
where we'd scale a view, drawing it into some pixels, then invalidate
that same area on the next frame, but the invalidation rectangle didn't
cover the same pixels as the device drew into.

The fix is to floor() the left/top pixels and ceil() the right/bottom
pixels of the transformed invalidation rectangle.

Issue #8971348 dropped pixel artifacts during some scaling operations

Change-Id: Iedb1afd5621dff43bf7a3919bdbd8d2251647fd2

1 files changed, 4 insertions, 4 deletions

diff --git a/core/java/android/view/View.java b/core/java/android/view/View.java
index 7f09a6a..0cd7c6e 100644
--- a/core/java/android/view/View.java
+++ b/core/java/android/view/View.java
@@ -10578,10 +10578,10 @@ public class View implements Drawable.Callback, KeyEvent.Callback,
             RectF boundingRect = mAttachInfo.mTmpTransformRect;
             boundingRect.set(rect);
             getMatrix().mapRect(boundingRect);
-            rect.set((int) (boundingRect.left - 0.5f),
-                    (int) (boundingRect.top - 0.5f),
-                    (int) (boundingRect.right + 0.5f),
-                    (int) (boundingRect.bottom + 0.5f));
+            rect.set((int) Math.floor(boundingRect.left),
+                    (int) Math.floor(boundingRect.top),
+                    (int) Math.ceil(boundingRect.right),
+                    (int) Math.ceil(boundingRect.bottom));
         }
     }