[Carousel] Shift keylines in contained strategies when there exists padding, and clipToPadding=false

PiperOrigin-RevId: 595162372

Author: imhappi

lib/java/com/google/android/material/carousel/CarouselLayoutManager.java

@@ -224,6 +224,32 @@ public int getCarouselAlignment() {
     return carouselAlignment;
   }
 
+  private int getLeftOrTopPaddingForKeylineShift() {
+    // TODO(b/316969331): Fix keyline shifting by decreasing carousel size when carousel is clipped
+    // to padding.
+    // TODO(b/316968490): Fix keyline shifting by adjusting cutoffs if strategy is not contained.
+    if (getClipToPadding() || !carouselStrategy.isContained()) {
+      return 0;
+    }
+    if (getOrientation() == VERTICAL) {
+      return getPaddingTop();
+    }
+    return getPaddingLeft();
+  }
+
+  private int getRightOrBottomPaddingForKeylineShift() {
+    // TODO(b/316969331): Fix keyline shifting by decreasing carousel size when carousel is clipped
+    // to padding.
+    // TODO(b/316968490): Fix keyline shifting by adjusting cutoffs if strategy is not contained.
+    if (getClipToPadding() || !carouselStrategy.isContained()) {
+      return 0;
+    }
+    if (getOrientation() == VERTICAL) {
+      return getPaddingBottom();
+    }
+    return getPaddingRight();
+  }
+
   @Override
   public LayoutParams generateDefaultLayoutParams() {
     return new LayoutParams(
@@ -319,7 +345,21 @@ private void recalculateKeylineStateList(Recycler recycler) {
     keylineStateList =
         KeylineStateList.from(
             this,
-            isLayoutRtl() ? KeylineState.reverse(keylineState, getContainerSize()) : keylineState);
+            isLayoutRtl() ? KeylineState.reverse(keylineState, getContainerSize()) : keylineState,
+            getItemMargins(),
+            getLeftOrTopPaddingForKeylineShift(),
+            getRightOrBottomPaddingForKeylineShift());
+  }
+
+  private int getItemMargins() {
+    if (getChildCount() > 0) {
+      LayoutParams lp = (LayoutParams) getChildAt(0).getLayoutParams();
+      if (orientationHelper.orientation == HORIZONTAL) {
+        return lp.leftMargin + lp.rightMargin;
+      }
+      return lp.topMargin + lp.bottomMargin;
+    }
+    return 0;
   }
 
   /**
@@ -795,9 +835,9 @@ private int calculateStartScroll(@NonNull KeylineStateList stateList) {
     KeylineState startState = isRtl ? stateList.getEndState() : stateList.getStartState();
     Keyline startFocalKeyline =
         isRtl ? startState.getLastFocalKeyline() : startState.getFirstFocalKeyline();
-    float firstItemDistanceFromStart = getPaddingStart() * (isRtl ? 1 : -1);
     float firstItemStart = addStart(startFocalKeyline.loc, startState.getItemSize() / 2F);
-    return (int) (firstItemDistanceFromStart + getParentStart() - firstItemStart);
+    // This value already includes any padding since startFocalKeyline.loc is already adjusted
+    return (int) (getParentStart() - firstItemStart);
   }
 
   /**
@@ -811,9 +851,10 @@ private int calculateEndScroll(State state, KeylineStateList stateList) {
         isRtl ? endState.getFirstFocalKeyline() : endState.getLastFocalKeyline();
     // Get the total distance from the first item to the last item in the end-to-end model
     float lastItemDistanceFromFirstItem =
-        (((state.getItemCount() - 1) * endState.getItemSize()) + getPaddingEnd())
-            * (isRtl ? -1F : 1F);
+        ((state.getItemCount() - 1) * endState.getItemSize()) * (isRtl ? -1F : 1F);
 
+    float endPadding =
+        isRtl ? -endFocalKeyline.leftOrTopPaddingShift : endFocalKeyline.rightOrBottomPaddingShift;
     float endFocalLocDistanceFromStart = endFocalKeyline.loc - getParentStart();
     float endFocalLocDistanceFromEnd = getParentEnd() - endFocalKeyline.loc;
 
@@ -824,7 +865,10 @@ private int calculateEndScroll(State state, KeylineStateList stateList) {
         (int)
             (lastItemDistanceFromFirstItem
                 - endFocalLocDistanceFromStart
-                + endFocalLocDistanceFromEnd);
+                + endFocalLocDistanceFromEnd
+                // If there is padding, adjust for the extra padding offset since offset is
+                // implicitly added from both endFocalLocDistance calculations.
+                + endPadding);
 
     return isRtl ? min(0, endScroll) : max(0, endScroll);
   }

lib/java/com/google/android/material/carousel/KeylineState.java

@@ -140,6 +140,17 @@ Keyline getLastNonAnchorKeyline() {
     return null;
   }
 
+  /** Returns how many non-anchor keylines. */
+  int getNumberOfNonAnchorKeylines() {
+    int anchorKeylines = 0;
+    for (Keyline keyline : keylines) {
+      if (keyline.isAnchor) {
+        anchorKeylines += 1;
+      }
+    }
+    return keylines.size() - anchorKeylines;
+  }
+
   /**
    * Linearly interpolate between two {@link KeylineState}s.
    *
@@ -337,7 +348,9 @@ Builder addKeyline(
         float maskedItemSize,
         boolean isFocal,
         boolean isAnchor,
-        float cutoff) {
+        float cutoff,
+        float leftOrTopPaddingShift,
+        float rightOrBottomPaddingShift) {
       if (maskedItemSize <= 0F) {
         return this;
       }
@@ -353,7 +366,8 @@ Builder addKeyline(
       }
 
       Keyline tmpKeyline =
-          new Keyline(UNKNOWN_LOC, offsetLoc, mask, maskedItemSize, isAnchor, cutoff);
+          new Keyline(UNKNOWN_LOC, offsetLoc, mask, maskedItemSize, isAnchor, cutoff,
+              leftOrTopPaddingShift, rightOrBottomPaddingShift);
       if (isFocal) {
         if (tmpFirstFocalKeyline == null) {
           tmpFirstFocalKeyline = tmpKeyline;
@@ -388,6 +402,44 @@ Builder addKeyline(
       return this;
     }
 
+    /**
+     * Adds a keyline along the scrolling axis where an object should be masked by the given {@code
+     * mask} and positioned at {@code offsetLoc}.
+     *
+     * <p>Note that calls to {@link #addKeyline(float, float, float, boolean, boolean)} and {@link
+     * #addKeylineRange(float, float, float, int)} are added in order. Typically, this means
+     * keylines should be added in order of ascending {@code offsetLoc}. The first and last keylines
+     * added are 'anchor' keylines that mark the start and ends of the keylines. These keylines do
+     * not shift when scrolled.
+     *
+     * <p>Note also that {@code isFocal} and {@code isAnchor} cannot be true at the same time as
+     * anchor keylines refer to keylines offscreen that dictate the ends of the keylines.
+     *
+     * @param offsetLoc The location of this keyline along the scrolling axis. An offsetLoc of 0
+     *     will be at the start of the scroll container.
+     * @param mask The percentage of a child's full size that it should be masked by when its center
+     *     is at {@code offsetLoc}. 0 is fully unmasked and 1 is fully masked.
+     * @param maskedItemSize The total size of this item when masked. This might differ from {@code
+     *     itemSize - (itemSize * mask)} depending on how margins are included in the {@code mask}.
+     * @param isFocal Whether this keyline is considered part of the focal range. Typically, this is
+     *     when {@code mask} is equal to 0.
+     * @param isAnchor Whether this keyline is an anchor keyline. Anchor keylines do not shift when
+     *     keylines are shifted.
+     * @param cutoff How much the keyline item is out the bounds of the available space.
+     */
+    @NonNull
+    @CanIgnoreReturnValue
+    Builder addKeyline(
+        float offsetLoc,
+        @FloatRange(from = 0.0F, to = 1.0F) float mask,
+        float maskedItemSize,
+        boolean isFocal,
+        boolean isAnchor,
+        float cutoff) {
+      return addKeyline(offsetLoc, mask, maskedItemSize, isFocal, isAnchor, cutoff,
+          0, 0);
+    }
+
     /**
      * Adds a keyline along the scrolling axis where an object should be masked by the given {@code
      * mask} and positioned at {@code offsetLoc}. This method also calculates the amount that a
@@ -537,7 +589,9 @@ KeylineState build() {
                 tmpKeyline.mask,
                 tmpKeyline.maskedItemSize,
                 tmpKeyline.isAnchor,
-                tmpKeyline.cutoff);
+                tmpKeyline.cutoff,
+                tmpKeyline.leftOrTopPaddingShift,
+                tmpKeyline.rightOrBottomPaddingShift);
         keylines.add(keyline);
       }
 
@@ -574,6 +628,8 @@ static final class Keyline {
     final float maskedItemSize;
     final boolean isAnchor;
     final float cutoff;
+    final float leftOrTopPaddingShift;
+    final float rightOrBottomPaddingShift;
 
     /**
      * Creates a non-anchor keyline along a scroll axis.
@@ -587,7 +643,8 @@ static final class Keyline {
      * @param maskedItemSize The size of this item when masked.
      */
     Keyline(float loc, float locOffset, float mask, float maskedItemSize) {
-      this(loc, locOffset, mask, maskedItemSize, /* isAnchor= */ false, 0);
+      this(loc, locOffset, mask, maskedItemSize, /* isAnchor= */ false, 0,
+          0, 0);
     }
 
     /**
@@ -603,20 +660,28 @@ static final class Keyline {
      * @param isAnchor Whether or not the keyline is an anchor keyline (keylines at the end that do
      *     not shift).
      * @param cutoff The amount by which the keyline item is cut off by the bounds of the carousel.
+     * @param leftOrTopPaddingShift The amount by which this keyline was shifted to account for left
+     *     or top padding
+     * @param rightOrBottomPaddingShift The amount by which this keyline was shifted to account for
+     *     right or bottom padding
      */
     Keyline(
         float loc,
         float locOffset,
         float mask,
         float maskedItemSize,
         boolean isAnchor,
-        float cutoff) {
+        float cutoff,
+        float leftOrTopPaddingShift,
+        float rightOrBottomPaddingShift) {
       this.loc = loc;
       this.locOffset = locOffset;
       this.mask = mask;
       this.maskedItemSize = maskedItemSize;
       this.isAnchor = isAnchor;
       this.cutoff = cutoff;
+      this.leftOrTopPaddingShift = leftOrTopPaddingShift;
+      this.rightOrBottomPaddingShift = rightOrBottomPaddingShift;
     }
 
     /** Linearly interpolates between two keylines and returns the interpolated object. */