Fix rounding error when constructing Rect from FloatRect

Current rounding logic does not handle negative values
correctly. FloatRect(-1080,...) is converted to Rect(-1079,...)
Fix this by using the standard rounding function.

Flag: EXEMPT build error (b/350967139)
Bug: 310950423
Test: presubmit
Change-Id: Ib8c5c393040149225e5b2bc858c21894e306a456

2 files changed, 14 insertions, 6 deletions

diff --git a/libs/ui/include/ui/Rect.h b/libs/ui/include/ui/Rect.h
index 2eb9330cc9..2307b44eb2 100644
--- a/libs/ui/include/ui/Rect.h
+++ b/libs/ui/include/ui/Rect.h
@@ -74,12 +74,10 @@ public:
     }
 
     inline explicit Rect(const FloatRect& floatRect) {
-        // Ideally we would use std::round, but we don't want to add an STL
-        // dependency here, so we use an approximation
-        left = static_cast<int32_t>(floatRect.left + 0.5f);
-        top = static_cast<int32_t>(floatRect.top + 0.5f);
-        right = static_cast<int32_t>(floatRect.right + 0.5f);
-        bottom = static_cast<int32_t>(floatRect.bottom + 0.5f);
+        left = static_cast<int32_t>(std::round(floatRect.left));
+        top = static_cast<int32_t>(std::round(floatRect.top));
+        right = static_cast<int32_t>(std::round(floatRect.right));
+        bottom = static_cast<int32_t>(std::round(floatRect.bottom));
     }
 
     inline explicit Rect(const ui::Size& size) {
diff --git a/libs/ui/tests/Rect_test.cpp b/libs/ui/tests/Rect_test.cpp
index 9cc36bb15b..c3c8bd9fa4 100644
--- a/libs/ui/tests/Rect_test.cpp
+++ b/libs/ui/tests/Rect_test.cpp
@@ -99,6 +99,16 @@ TEST(RectTest, constructFromFloatRect) {
         EXPECT_EQ(30, rect.right);
         EXPECT_EQ(40, rect.bottom);
     }
+
+    EXPECT_EQ(Rect(0, 1, -1, 0), Rect(FloatRect(0.f, 1.f, -1.f, 0.f)));
+    EXPECT_EQ(Rect(100000, 100000, -100000, -100000),
+              Rect(FloatRect(100000.f, 100000.f, -100000.f, -100000.f)));
+
+    // round down if < .5
+    EXPECT_EQ(Rect(0, 1, -1, 0), Rect(FloatRect(0.4f, 1.1f, -1.499f, 0.1f)));
+
+    // round up if >= .5
+    EXPECT_EQ(Rect(20, 20, -20, -20), Rect(FloatRect(19.5f, 19.9f, -19.5f, -19.9f)));
 }
 
 TEST(RectTest, makeInvalid) {