Revert "Remove obsolete shadow logic from StackScrollAlgorithm updateChildZValue"

This reverts commit fcb74a62f2.

Reason for revert: To fix multi-huns bug, because the previous change accidentally removed multi-huns' z-value order.
Bug: 266774171
Test: StackScrollAlgorithmTest

Change-Id: Ie3500b867851647b1647ff4791864573a9c438ae

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

@@ -871,7 +871,8 @@ public class StackScrollAlgorithm {
         }
 
         for (int i = childCount - 1; i >= 0; i--) {
-            updateChildZValue(i, algorithmState, ambientState, i == topHunIndex);
+            childrenOnTop = updateChildZValue(i, childrenOnTop,
+                    algorithmState, ambientState, i == topHunIndex);
         }
     }
 
@@ -881,11 +882,15 @@ 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 void updateChildZValue(int i,
-                                     StackScrollAlgorithmState algorithmState,
-                                     AmbientState ambientState,
-                                     boolean isTopHun) {
+    protected float updateChildZValue(int i, float childrenOnTop,
+                                      StackScrollAlgorithmState algorithmState,
+                                      AmbientState ambientState,
+                                      boolean isTopHun) {
         ExpandableView child = algorithmState.visibleChildren.get(i);
         ExpandableViewState childViewState = child.getViewState();
         float baseZ = ambientState.getBaseZHeight();
@@ -899,16 +904,22 @@ 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 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);
+            // 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);
             }
+            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
@@ -936,14 +947,15 @@ public class StackScrollAlgorithm {
         }
 
         // Handles HUN shadow when shade is closed.
-        // 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.
+        // While HUN is showing and Shade is closed: 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)
@@ -526,6 +526,7 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         // When: updateChildZValue() is called for the top HUN
         stackScrollAlgorithm.updateChildZValue(
                 /* i= */ 0,
+                /* childrenOnTop= */ 0.0f,
                 /* StackScrollAlgorithmState= */ algorithmState,
                 /* ambientState= */ ambientState,
                 /* shouldElevateHun= */ true
@@ -545,7 +546,7 @@ 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()
@@ -555,6 +556,7 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         // When: updateChildZValue() is called for the top HUN
         stackScrollAlgorithm.updateChildZValue(
                 /* i= */ 0,
+                /* childrenOnTop= */ 0.0f,
                 /* StackScrollAlgorithmState= */ algorithmState,
                 /* ambientState= */ ambientState,
                 /* shouldElevateHun= */ true
@@ -578,7 +580,7 @@ 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 +
@@ -589,6 +591,7 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         // When: updateChildZValue() is called for the top HUN
         stackScrollAlgorithm.updateChildZValue(
                 /* i= */ 0,
+                /* childrenOnTop= */ 0.0f,
                 /* StackScrollAlgorithmState= */ algorithmState,
                 /* ambientState= */ ambientState,
                 /* shouldElevateHun= */ true
@@ -608,7 +611,7 @@ 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
@@ -619,6 +622,7 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         // When: updateChildZValue() is called for the top HUN
         stackScrollAlgorithm.updateChildZValue(
                 /* i= */ 0,
+                /* childrenOnTop= */ 0.0f,
                 /* StackScrollAlgorithmState= */ algorithmState,
                 /* ambientState= */ ambientState,
                 /* shouldElevateHun= */ true
@@ -638,7 +642,7 @@ 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
@@ -650,6 +654,7 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
         // When: updateChildZValue() is called for the top HUN
         stackScrollAlgorithm.updateChildZValue(
                 /* i= */ 0,
+                /* childrenOnTop= */ 0.0f,
                 /* StackScrollAlgorithmState= */ algorithmState,
                 /* ambientState= */ ambientState,
                 /* shouldElevateHun= */ true
@@ -664,7 +669,7 @@ class StackScrollAlgorithmTest : SysuiTestCase() {
     private fun createHunViewMock(
             isShadeOpen: Boolean,
             fullyVisible: Boolean,
-            headerVisibleAmount: Float,
+            headerVisibleAmount: Float
     ) =
             mock<ExpandableNotificationRow>().apply {
                 val childViewStateMock = createHunChildViewState(isShadeOpen, fullyVisible)
@@ -675,10 +680,7 @@ 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