Remove obsolete shadow logic from StackScrollAlgorithm updateChildZValue

Removed childrenOnTop. When you send a bunch of delayed HUNs, the newest HUN pushes the previously pinned HUN downwards, so there's always a max of one pinned HUN. Thus childrenOnTop is no longer needed.

Bug: 259278944
Test: StackScrollAlgorithmTest
Change-Id: I47446170c3199769e78521f80ed3982e2e8554a4

packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/StackScrollAlgorithm.java

@@ -871,8 +871,7 @@ public class StackScrollAlgorithm {
         }
 
         for (int i = childCount - 1; i >= 0; i--) {
-            childrenOnTop = updateChildZValue(i, childrenOnTop,
-                    algorithmState, ambientState, i == topHunIndex);
+            updateChildZValue(i, algorithmState, ambientState, i == topHunIndex);
         }
     }
 
@@ -882,15 +881,11 @@ public class StackScrollAlgorithm {
      *
      * @param isTopHun      Whether the child is a top HUN. A top HUN means a HUN that shows on the
      *                      vertically top of screen. Top HUNs should have drop shadows
-     * @param childrenOnTop It is greater than 0 when there's an existing HUN that is elevated
-     * @return childrenOnTop The decimal part represents the fraction of the elevated HUN's height
-     *                      that overlaps with QQS Panel. The integer part represents the count of
-     *                      previous HUNs whose Z positions are greater than 0.
      */
-    protected float updateChildZValue(int i, float childrenOnTop,
-                                      StackScrollAlgorithmState algorithmState,
-                                      AmbientState ambientState,
-                                      boolean isTopHun) {
+    protected void updateChildZValue(int i,
+                                     StackScrollAlgorithmState algorithmState,
+                                     AmbientState ambientState,
+                                     boolean isTopHun) {
         ExpandableView child = algorithmState.visibleChildren.get(i);
         ExpandableViewState childViewState = child.getViewState();
         float baseZ = ambientState.getBaseZHeight();
@@ -904,22 +899,16 @@ public class StackScrollAlgorithm {
             // Handles HUN shadow when Shade is opened, and AmbientState.mScrollY > 0
             // Calculate the HUN's z-value based on its overlapping fraction with QQS Panel.
             // When scrolling down shade to make HUN back to in-position in Notification Panel,
-            // The over-lapping fraction goes to 0, and shadows hides gradually.
-            if (childrenOnTop != 0.0f) {
-                // To elevate the later HUN over previous HUN
-                childrenOnTop++;
-            } else {
-                float overlap = ambientState.getTopPadding()
-                        + ambientState.getStackTranslation() - childViewState.getYTranslation();
-                // To prevent over-shadow during HUN entry
-                childrenOnTop += Math.min(
-                        1.0f,
-                        overlap / childViewState.height
-                );
-                MathUtils.saturate(childrenOnTop);
+            // the overlapFraction goes to 0, and the pinned HUN's shadows hides gradually.
+            float overlap = ambientState.getTopPadding()
+                    + ambientState.getStackTranslation() - childViewState.getYTranslation();
+
+            if (childViewState.height > 0) { // To avoid 0/0 problems
+                // To prevent over-shadow
+                float overlapFraction = MathUtils.saturate(overlap / childViewState.height);
+                childViewState.setZTranslation(baseZ
+                        + overlapFraction * mPinnedZTranslationExtra);
             }
-            childViewState.setZTranslation(baseZ
-                    + childrenOnTop * mPinnedZTranslationExtra);
         } else if (isTopHun) {
             // In case this is a new view that has never been measured before, we don't want to
             // elevate if we are currently expanded more than the notification
@@ -947,15 +936,14 @@ public class StackScrollAlgorithm {
         }
 
         // Handles HUN shadow when shade is closed.
-        // While HUN is showing and Shade is closed: headerVisibleAmount stays 0, shadow stays.
+        // While shade is closed, and during HUN's entry: headerVisibleAmount stays 0, shadow stays.
+        // While shade is closed, and HUN is showing: headerVisibleAmount stays 0, shadow stays.
         // During HUN-to-Shade (eg. dragging down HUN to open Shade): headerVisibleAmount goes
         // gradually from 0 to 1, shadow hides gradually.
         // Header visibility is a deprecated concept, we are using headerVisibleAmount only because
         // this value nicely goes from 0 to 1 during the HUN-to-Shade process.
-
         childViewState.setZTranslation(childViewState.getZTranslation()
                 + (1.0f - child.getHeaderVisibleAmount()) * mPinnedZTranslationExtra);
-        return childrenOnTop;
     }
 
     public void setIsExpanded(boolean isExpanded) {

packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/stack/StackScrollAlgorithmTest.kt

@@ -518,7 +518,7 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         val childHunView = createHunViewMock(
                 isShadeOpen = true,
                 fullyVisible = false,
-                headerVisibleAmount = 1f
+                headerVisibleAmount = 1f,
         )
         val algorithmState = StackScrollAlgorithm.StackScrollAlgorithmState()
         algorithmState.visibleChildren.add(childHunView)
@@ -526,7 +526,6 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         // When: updateChildZValue() is called for the top HUN
         stackScrollAlgorithm.updateChildZValue(
                 /* i= */ 0,
-                /* childrenOnTop= */ 0.0f,
                 /* StackScrollAlgorithmState= */ algorithmState,
                 /* ambientState= */ ambientState,
                 /* shouldElevateHun= */ true
@@ -546,7 +545,7 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         val childHunView = createHunViewMock(
                 isShadeOpen = true,
                 fullyVisible = false,
-                headerVisibleAmount = 1f
+                headerVisibleAmount = 1f,
         )
         // Use half of the HUN's height as overlap
         childHunView.viewState.yTranslation = (childHunView.viewState.height + 1 shr 1).toFloat()
@@ -556,7 +555,6 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         // When: updateChildZValue() is called for the top HUN
         stackScrollAlgorithm.updateChildZValue(
                 /* i= */ 0,
-                /* childrenOnTop= */ 0.0f,
                 /* StackScrollAlgorithmState= */ algorithmState,
                 /* ambientState= */ ambientState,
                 /* shouldElevateHun= */ true
@@ -580,7 +578,7 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         val childHunView = createHunViewMock(
                 isShadeOpen = true,
                 fullyVisible = true,
-                headerVisibleAmount = 1f
+                headerVisibleAmount = 1f,
         )
         // HUN doesn't overlap with QQS Panel
         childHunView.viewState.yTranslation = ambientState.topPadding +
@@ -591,7 +589,6 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         // When: updateChildZValue() is called for the top HUN
         stackScrollAlgorithm.updateChildZValue(
                 /* i= */ 0,
-                /* childrenOnTop= */ 0.0f,
                 /* StackScrollAlgorithmState= */ algorithmState,
                 /* ambientState= */ ambientState,
                 /* shouldElevateHun= */ true
@@ -611,7 +608,7 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         val childHunView = createHunViewMock(
                 isShadeOpen = false,
                 fullyVisible = false,
-                headerVisibleAmount = 0f
+                headerVisibleAmount = 0f,
         )
         childHunView.viewState.yTranslation = 0f
         // Shade is closed, thus childHunView's headerVisibleAmount is 0
@@ -622,7 +619,6 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         // When: updateChildZValue() is called for the top HUN
         stackScrollAlgorithm.updateChildZValue(
                 /* i= */ 0,
-                /* childrenOnTop= */ 0.0f,
                 /* StackScrollAlgorithmState= */ algorithmState,
                 /* ambientState= */ ambientState,
                 /* shouldElevateHun= */ true
@@ -642,7 +638,7 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         val childHunView = createHunViewMock(
                 isShadeOpen = false,
                 fullyVisible = false,
-                headerVisibleAmount = 0.5f
+                headerVisibleAmount = 0.5f,
         )
         childHunView.viewState.yTranslation = 0f
         // Shade is being opened, thus childHunView's headerVisibleAmount is between 0 and 1
@@ -654,7 +650,6 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         // When: updateChildZValue() is called for the top HUN
         stackScrollAlgorithm.updateChildZValue(
                 /* i= */ 0,
-                /* childrenOnTop= */ 0.0f,
                 /* StackScrollAlgorithmState= */ algorithmState,
                 /* ambientState= */ ambientState,
                 /* shouldElevateHun= */ true
@@ -669,7 +664,7 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
     private fun createHunViewMock(
             isShadeOpen: Boolean,
             fullyVisible: Boolean,
-            headerVisibleAmount: Float
+            headerVisibleAmount: Float,
     ) =
             mock<ExpandableNotificationRow>().apply {
                 val childViewStateMock = createHunChildViewState(isShadeOpen, fullyVisible)
@@ -680,7 +675,10 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
             }
 
 
-    private fun createHunChildViewState(isShadeOpen: Boolean, fullyVisible: Boolean) =
+    private fun createHunChildViewState(
+            isShadeOpen: Boolean,
+            fullyVisible: Boolean,
+    ) =
             ExpandableViewState().apply {
                 // Mock the HUN's height with ambientState.topPadding +
                 // ambientState.stackTranslation