[Carousel] Ensure that masks are pushed out beyond the parent bounds if they are _on_ the parent bounds

PiperOrigin-RevId: 540105089

Author: imhappi

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

@@ -784,21 +784,35 @@ private void updateChildMaskForLocation(
     float maskWidth = lerp(0F, childWidth / 2F, 0F, 1F, maskProgress);
     RectF maskRect = new RectF(maskWidth, 0F, (childWidth - maskWidth), childHeight);
 
+    float offsetCx = calculateChildOffsetCenterForLocation(child, childCenterLocation, range);
+    float maskedLeft = offsetCx - (maskRect.width() / 2F);
+    float maskedRight = offsetCx + (maskRect.width() / 2F);
+
     // If the carousel is a CONTAINED carousel, ensure the mask collapses against the side of the
     // container instead of bleeding and being clipped by the RecyclerView's bounds.
     // Only do this if there is only one side of the mask that is out of bounds; if
     // both sides are out of bounds on the same side, then the whole mask is out of view.
     if (carouselStrategy.isContained()) {
-      float offsetCx = calculateChildOffsetCenterForLocation(child, childCenterLocation, range);
-      float maskedLeft = offsetCx - (maskRect.width() / 2F);
-      float maskedRight = offsetCx + (maskRect.width() / 2F);
-      if (maskedLeft < getParentLeft() && maskedRight >= getParentLeft()) {
-        maskRect.left = maskRect.left + (getParentLeft() - maskedLeft);
+      if (maskedLeft < getParentLeft() && maskedRight > getParentLeft()) {
+        float diff = getParentLeft() - maskedLeft;
+        maskRect.left += diff;
+        maskedLeft += diff;
       }
-      if (maskedRight > getParentRight() && maskedLeft <= getParentRight()) {
-        maskRect.right = max(maskRect.right - (maskedRight - getParentRight()), maskRect.left);
+      if (maskedRight > getParentRight() && maskedLeft < getParentRight()) {
+        float diff = maskedRight - getParentRight();
+        maskRect.right = max(maskRect.right - diff, maskRect.left);
+        maskedRight = max(maskedRight - diff, maskedLeft);
       }
     }
+
+    // 'Push out' any masks that are on the parent edge by rounding up/down and adding or
+    // subtracting a pixel. Otherwise, the mask on the 'edge' looks like it has a width of 1 pixel.
+    if (maskedRight <= getParentLeft()) {
+      maskRect.right = (float) Math.floor(maskRect.right) - 1;
+    }
+    if (maskedLeft >= getParentRight()) {
+      maskRect.left = (float) Math.ceil(maskRect.left) + 1;
+    }
     ((Maskable) child).setMaskRectF(maskRect);
   }
 

lib/javatests/com/google/android/material/carousel/CarouselLayoutManagerTest.java

@@ -309,6 +309,68 @@ public void testUncontainedLayout_allowsLastItemToBleed() throws Throwable {
     assertThat(lastItemMask.right).isGreaterThan(DEFAULT_RECYCLER_VIEW_WIDTH);
   }
 
+  @Test
+  public void testMasksLeftOfParent_areRoundedDown() throws Throwable {
+    layoutManager.setCarouselStrategy(
+        new TestContainmentCarouselStrategy(/* isContained= */ false));
+    setAdapterItems(recyclerView, layoutManager, adapter, createDataSetWithSize(10));
+    scrollHorizontallyBy(recyclerView, layoutManager, 900);
+
+    for (int i = 0; i < recyclerView.getChildCount(); i++) {
+      View child = recyclerView.getChildAt(i);
+      Rect itemMask = getMaskRectOffsetToRecyclerViewCoords((MaskableFrameLayout) child);
+      assertThat(itemMask.right).isNotEqualTo(0);
+    }
+  }
+
+  @Test
+  public void testMaskOnLeftParentEdge_areRoundedUp() throws Throwable {
+    layoutManager.setCarouselStrategy(
+        new TestContainmentCarouselStrategy(/* isContained= */ false));
+    setAdapterItems(recyclerView, layoutManager, adapter, createDataSetWithSize(10));
+    // Scroll to end
+    scrollToPosition(recyclerView, layoutManager, 9);
+
+    // Carousel strategy at end is {small, large}. Last child will be large item, second last
+    // child will be small item. So third last child's right mask edge should not show.
+    Rect thirdLastChildMask =
+        getMaskRectOffsetToRecyclerViewCoords(
+            (MaskableFrameLayout) recyclerView.getChildAt(recyclerView.getChildCount() - 3));
+    assertThat(thirdLastChildMask.right).isLessThan(0);
+    assertThat(thirdLastChildMask.right).isAtLeast(thirdLastChildMask.left);
+  }
+
+  @Test
+  public void testMaskOnRightBoundary_areRoundedUp() throws Throwable {
+    layoutManager.setCarouselStrategy(
+        new TestContainmentCarouselStrategy(/* isContained= */ false));
+    setAdapterItems(recyclerView, layoutManager, adapter, createDataSetWithSize(10));
+    scrollHorizontallyBy(recyclerView, layoutManager, 900);
+
+    // For every child, assert that the mask left edge is located beyond the recycler view
+    // width (parent's right edge).
+    for (int i = recyclerView.getChildCount() - 1; i >= 0; i--) {
+      View child = recyclerView.getChildAt(i);
+      Rect itemMask = getMaskRectOffsetToRecyclerViewCoords((MaskableFrameLayout) child);
+      assertThat(itemMask.left).isNotEqualTo(DEFAULT_RECYCLER_VIEW_WIDTH);
+    }
+  }
+
+  @Test
+  public void testMaskOnRightParentEdge_areRoundedUp() throws Throwable {
+    layoutManager.setCarouselStrategy(
+        new TestContainmentCarouselStrategy(/* isContained= */ false));
+    setAdapterItems(recyclerView, layoutManager, adapter, createDataSetWithSize(10));
+
+    // Carousel strategy is {large, small}. First child will be large item, second child will
+    // be small item, so the third child's left mask edge should not show up at the right parent
+    // edge.
+    Rect thirdChildMask =
+        getMaskRectOffsetToRecyclerViewCoords((MaskableFrameLayout) recyclerView.getChildAt(2));
+    assertThat(thirdChildMask.left).isGreaterThan(DEFAULT_RECYCLER_VIEW_WIDTH);
+    assertThat(thirdChildMask.left).isAtMost(thirdChildMask.right);
+  }
+
   /**
    * Assigns explicit sizes to fixtures being used to construct the testing environment.
    *