Improve selection in the viewport (#720)

* improve selection in the viewport

* remove debug code

* updates following review feedback

- update API comments from /// to //! from
- add [[nodiscard]] attribute to member function
- move constructor implementations to .cpp files

* use lambda instead of ternary operator

* fix unit test failure caused by typo

Code/Framework/Tests/CursorStateTests.cpp

@@ -0,0 +1,54 @@
+/*
+ * All or portions of this file Copyright (c) Amazon.com, Inc. or its affiliates or
+ * its licensors.
+ *
+ * For complete copyright and license terms please see the LICENSE at the root of this
+ * distribution (the "License"). All use of this software is governed by the License,
+ * or, if provided, by the license below or the license accompanying this file. Do not
+ * remove or modify any license notices. This file is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *
+ */
+
+#include <AzCore/UnitTest/TestTypes.h>
+#include <AzFramework/Viewport/CursorState.h>
+
+namespace UnitTest
+{
+    using AzFramework::CursorState;
+    using AzFramework::ScreenVector;
+    using AzFramework::ScreenPoint;
+
+    class CursorStateFixture : public ::testing::Test
+    {
+    public:
+        CursorState m_cursorState;
+    };
+
+    TEST_F(CursorStateFixture, CursorStateHasZeroDeltaInitially)
+    {
+        using ::testing::Eq;
+        EXPECT_THAT(m_cursorState.CursorDelta(), Eq(ScreenVector(0, 0)));
+    }
+
+    TEST_F(CursorStateFixture, CursorStateReturnsZeroDeltaAfterSingleMoveAndUpdate)
+    {
+        using ::testing::Eq;
+
+        m_cursorState.SetCurrentPosition(ScreenPoint(10, 10));
+        m_cursorState.Update();
+
+        EXPECT_THAT(m_cursorState.CursorDelta(), Eq(ScreenVector(0, 0)));
+    }
+
+    TEST_F(CursorStateFixture, CursorStateReturnsDeltaAfterSecondMoveAndUpdate)
+    {
+        using ::testing::Eq;
+
+        m_cursorState.SetCurrentPosition(ScreenPoint(10, 10));
+        m_cursorState.Update();
+        m_cursorState.SetCurrentPosition(ScreenPoint(15, 22));
+
+        EXPECT_THAT(m_cursorState.CursorDelta(), Eq(ScreenVector(5, 12)));
+    }
+} // namespace UnitTest