Replace PxPosition with Offset

Relnote: "In order to consolidate the
number of classes used to represent
positioning information, standardize
on usage of the Offset class instead
of PxPosition. This provides the benefits
of an inline class to leverage a long
to pack 2 float values to represent x
and y offsets represented as floats."

Bug: 157948366
Test: re-ran compose tests
Change-Id: I3ad983207bc37af20afac03e2cd09b4240777687

diff --git a/ui/ui-core/src/main/java/androidx/ui/core/selection/SelectionManager.kt b/ui/ui-core/src/main/java/androidx/ui/core/selection/SelectionManager.kt
index 5665510..e0fb3dd 100644
--- a/ui/ui-core/src/main/java/androidx/ui/core/selection/SelectionManager.kt
+++ b/ui/ui-core/src/main/java/androidx/ui/core/selection/SelectionManager.kt

@@ -33,7 +33,7 @@
 import androidx.ui.text.AnnotatedString
 import androidx.ui.text.length
 import androidx.ui.text.subSequence
-import androidx.ui.unit.PxPosition
+import androidx.ui.geometry.Offset
 import kotlin.math.max
 import kotlin.math.min
 
@@ -87,13 +87,13 @@
      * The beginning position of the drag gesture. Every time a new drag gesture starts, it wil be
      * recalculated.
      */
-    private var dragBeginPosition = PxPosition.Origin
+    private var dragBeginPosition = Offset.Zero
 
     /**
      * The total distance being dragged of the drag gesture. Every time a new drag gesture starts,
      * it will be zeroed out.
      */
-    private var dragTotalDistance = PxPosition.Origin
+    private var dragTotalDistance = Offset.Zero
 
     /**
      * A flag to check if the selection start or end handle is being dragged.
@@ -109,7 +109,7 @@
      * It is a [State] so reading it during the composition will cause recomposition every time
      * the position has been changed.
      */
-    var startHandlePosition by mutableStateOf<PxPosition?>(null, areEquivalent = StructurallyEqual)
+    var startHandlePosition by mutableStateOf<Offset?>(null, areEquivalent = StructurallyEqual)
         private set
 
     /**
@@ -118,7 +118,7 @@
      * It is a [State] so reading it during the composition will cause recomposition every time
      * the position has been changed.
      */
-    var endHandlePosition by mutableStateOf<PxPosition?>(null, areEquivalent = StructurallyEqual)
+    var endHandlePosition by mutableStateOf<Offset?>(null, areEquivalent = StructurallyEqual)
         private set
 
     init {
@@ -171,8 +171,8 @@
      * Iterates over the handlers, gets the selection for each Composable, and merges all the
      * returned [Selection]s.
      *
-     * @param startPosition [PxPosition] for the start of the selection
-     * @param endPosition [PxPosition] for the end of the selection
+     * @param startPosition [Offset] for the start of the selection
+     * @param endPosition [Offset] for the end of the selection
      * @param longPress the selection is a result of long press
      * @param previousSelection previous selection
      *
@@ -181,8 +181,8 @@
      */
     // This function is internal for testing purposes.
     internal fun mergeSelections(
-        startPosition: PxPosition,
-        endPosition: PxPosition,
+        startPosition: Offset,
+        endPosition: Offset,
         longPress: Boolean = false,
         previousSelection: Selection? = null,
         isStartHandle: Boolean = true
@@ -307,7 +307,7 @@
 
             var startTop = localLayoutCoordinates.childToLocal(
                 startLayoutCoordinates,
-                PxPosition(
+                Offset(
                     0f,
                     selection.start.selectable.getBoundingBox(selection.start.offset).top
                 )
@@ -315,7 +315,7 @@
 
             var endTop = localLayoutCoordinates.childToLocal(
                 endLayoutCoordinates,
-                PxPosition(
+                Offset(
                     0.0f,
                     selection.end.selectable.getBoundingBox(selection.end.offset).top
                 )
@@ -342,15 +342,15 @@
         // Call mergeSelections with an out of boundary input to inform all text widgets to
         // cancel their individual selection.
         mergeSelections(
-            startPosition = PxPosition(-1f, -1f),
-            endPosition = PxPosition(-1f, -1f),
+            startPosition = Offset(-1f, -1f),
+            endPosition = Offset(-1f, -1f),
             previousSelection = selection
         )
         if (selection != null) onSelectionChange(null)
     }
 
     val longPressDragObserver = object : LongPressDragObserver {
-        override fun onLongPress(pxPosition: PxPosition) {
+        override fun onLongPress(pxPosition: Offset) {
             if (draggingHandle) return
             val coordinates = containerLayoutCoordinates
             if (coordinates == null || !coordinates.isAttached) return
@@ -369,12 +369,12 @@
             // selection never started
             if (selection == null) return
             // Zero out the total distance that being dragged.
-            dragTotalDistance = PxPosition.Origin
+            dragTotalDistance = Offset.Zero
         }
 
-        override fun onDrag(dragDistance: PxPosition): PxPosition {
+        override fun onDrag(dragDistance: Offset): Offset {
             // selection never started, did not consume any drag
-            if (selection == null) return PxPosition.Origin
+            if (selection == null) return Offset.Zero
 
             dragTotalDistance += dragDistance
             val newSelection = mergeSelections(
@@ -396,13 +396,13 @@
      * line's top offset, which is not included in current line's hit area. To be able to
      * hit current line, move up this y coordinates by 1 pixel.
      */
-    private fun getAdjustedCoordinates(position: PxPosition): PxPosition {
-        return PxPosition(position.x, position.y - 1f)
+    private fun getAdjustedCoordinates(position: Offset): Offset {
+        return Offset(position.x, position.y - 1f)
     }
 
     fun handleDragObserver(isStartHandle: Boolean): DragObserver {
         return object : DragObserver {
-            override fun onStart(downPosition: PxPosition) {
+            override fun onStart(downPosition: Offset) {
                 val selection = selection!!
                 // The LayoutCoordinates of the composable where the drag gesture should begin. This
                 // is used to convert the position of the beginning of the drag gesture from the
@@ -433,11 +433,11 @@
                 )
 
                 // Zero out the total distance that being dragged.
-                dragTotalDistance = PxPosition.Origin
+                dragTotalDistance = Offset.Zero
                 draggingHandle = true
             }
 
-            override fun onDrag(dragDistance: PxPosition): PxPosition {
+            override fun onDrag(dragDistance: Offset): Offset {
                 val selection = selection!!
                 dragTotalDistance += dragDistance
 
@@ -479,7 +479,7 @@
                 return dragDistance
             }
 
-            override fun onStop(velocity: PxPosition) {
+            override fun onStop(velocity: Offset) {
                 super.onStop(velocity)
                 draggingHandle = false
             }