Adapt and reland old position sticky implementation

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 565 matching lines @@
 
     else if (!style()->bottom().isAuto()
         && (!containingBlock->hasAutoHeightOrContainingBlockWithAutoHeight()
             || !style()->bottom().hasPercent()
             || containingBlock->stretchesToViewport()))
         offset.expand(0, -valueForLength(style()->bottom(), containingBlock->availableHeight()));
 
     return offset;
 }
 
+void LayoutBoxModelObject::computeStickyPositionConstraints(StickyPositionViewportConstraints& constraints, const LayoutRect& constrainingRect) const
+{
+    LayoutBlock* containingBlock = this->containingBlock();
+
+    LayoutRect containerContentRect = containingBlock->contentBoxRect();
+    LayoutUnit maxWidth = containingBlock->availableLogicalWidth();
+
+    // Sticky positioned element ignore any override logical width on the containing block (as they don't call
+    // containingBlockLogicalWidthForContent). It's unclear whether this is totally fine.
+    // Compute the container-relative area within which the sticky element is allowed to move.
+    containerContentRect.contractEdges(
+        minimumValueForLength(style()->marginTop(), maxWidth),
+        minimumValueForLength(style()->marginRight(), maxWidth),
+        minimumValueForLength(style()->marginBottom(), maxWidth),
+        minimumValueForLength(style()->marginLeft(), maxWidth));
+
+    // Map to the view to avoid including page scale factor.
+    constraints.setAbsoluteContainingBlockRect(LayoutRect(containingBlock->localToContainerQuad(FloatRect(containerContentRect), view()).boundingBox()));
+
+    LayoutRect stickyBoxRect = frameRectForStickyPositioning();
+    LayoutRect flippedStickyBoxRect = stickyBoxRect;
+    containingBlock->flipForWritingMode(flippedStickyBoxRect);
+    LayoutPoint stickyLocation = flippedStickyBoxRect.location();
+
+    // FIXME: sucks to call localToAbsolute again, but we can't just offset from the previously computed rect if there are transforms.
+    // Map to the view to avoid including page scale factor.
+    LayoutRect absContainerFrame = LayoutRect(containingBlock->localToContainerQuad(FloatRect(FloatPoint(), FloatSize(containingBlock->size())), view()).boundingBox());
+
+    if (containingBlock->hasOverflowClip()) {
+        LayoutSize scrollOffset(containingBlock->layer()->scrollableArea()->adjustedScrollOffset());
+        stickyLocation -= scrollOffset;
+    }
+
+    // We can't call localToAbsolute on |this| because that will recur. FIXME: For now, assume that |this| is not transformed.
+    LayoutRect absoluteStickyBoxRect(LayoutPoint(absContainerFrame.location()) + stickyLocation, flippedStickyBoxRect.size());
+    constraints.setAbsoluteStickyBoxRect(absoluteStickyBoxRect);
+
+    LayoutUnit horizontalOffsets = constraints.rightOffset() + constraints.leftOffset();

[chrishtr, 2015/10/06 17:08:33]

You're reading leftOffset() here and then setting it possibly below on line 635?
Why is that correct?

[flackr, 2015/10/07 20:38:12]

This is strange, I had lifted this from the old sticky code which seems to have
done the same. I've updated this to use the style right and left / top and
bottom.

+    bool skipRight = false;
+    bool skipLeft = false;
+    if (!style()->left().isAuto() && !style()->right().isAuto()) {
+        if (horizontalOffsets > containerContentRect.width()
+            || horizontalOffsets + containerContentRect.width() > constrainingRect.width()) {
+            skipRight = style()->isLeftToRightDirection();
+            skipLeft = !skipRight;
+        }
+    }
+
+    if (!style()->left().isAuto() && !skipLeft) {
+        constraints.setLeftOffset(minimumValueForLength(style()->left(), constrainingRect.width()));
+        constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeLeft);
+    }
+
+    if (!style()->right().isAuto() && !skipRight) {
+        constraints.setRightOffset(minimumValueForLength(style()->right(), constrainingRect.width()));
+        constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeRight);
+    }
+
+    bool skipBottom = false;
+    // FIXME(ostap): Exclude top or bottom edge offset depending on the writing mode when related
+    // sections are fixed in spec: http://lists.w3.org/Archives/Public/www-style/2014May/0286.html
+    LayoutUnit verticalOffsets = constraints.topOffset() + constraints.bottomOffset();
+    if (!style()->top().isAuto() && !style()->bottom().isAuto()) {
+        if (verticalOffsets > containerContentRect.height()
+            || verticalOffsets + containerContentRect.height() > constrainingRect.height()) {
+            skipBottom = true;
+        }
+    }
+
+    if (!style()->top().isAuto()) {
+        constraints.setTopOffset(minimumValueForLength(style()->top(), constrainingRect.height()));
+        constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeTop);
+    }
+
+    if (!style()->bottom().isAuto() && !skipBottom) {
+        constraints.setBottomOffset(minimumValueForLength(style()->bottom(), constrainingRect.height()));
+        constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeBottom);
+    }
+}
+
+static inline LayoutBox* findScrollAncestor(const Node* startNode)
+{
+    ASSERT(startNode->layoutObject());
+    LayoutBox* curBox = startNode->layoutObject()->containingBlock();
+
+    // Scrolling propagates along the containing block chain.
+    while (curBox && !curBox->isLayoutView()) {
+        if (curBox->hasOverflowClip())
+            return curBox;
+        curBox = curBox->containingBlock();
+    }
+
+    return nullptr;
+}
+
+LayoutRect LayoutBoxModelObject::computeStickyConstrainingRect() const

[chrishtr, 2015/10/06 17:08:33]

Is this part of implementing the 6-step algorithm spec'ed here?

https://drafts.csswg.org/css-position-3/#sticky-pos

[flackr, 2015/10/07 20:38:12]

No, this rectangle is the "viewport" used to determine if and by how much the
sticky element "projects" outside of the sticky constraint rectangle.

+{
+    LayoutRect constrainingRect;
+
+    ASSERT(hasLayer());
+    LayoutBox* enclosingClippingBox = findScrollAncestor(node());
+    if (enclosingClippingBox) {
+        LayoutRect clipRect = enclosingClippingBox->overflowClipRect(LayoutPoint());
+        clipRect.move(enclosingClippingBox->paddingLeft(), enclosingClippingBox->paddingTop());
+        clipRect.contract(LayoutSize(enclosingClippingBox->paddingLeft() + enclosingClippingBox->paddingRight(),
+            enclosingClippingBox->paddingTop() + enclosingClippingBox->paddingBottom()));
+        constrainingRect = LayoutRect(enclosingClippingBox->localToContainerQuad(FloatRect(clipRect), view()).boundingBox());
+    } else {
+        constrainingRect = LayoutRect(view()->frameView()->visibleContentRect());
+    }
+
+    return constrainingRect;
+}
+
+LayoutSize LayoutBoxModelObject::stickyPositionOffset() const
+{
+    LayoutRect constrainingRect = computeStickyConstrainingRect();
+    StickyPositionViewportConstraints constraints;
+    computeStickyPositionConstraints(constraints, constrainingRect);
+
+    // The sticky offset is physical, so we can just return the delta computed in absolute coords (though it may be wrong with transforms).
+    return LayoutSize(constraints.computeStickyOffset(constrainingRect));
+}
+
 LayoutPoint LayoutBoxModelObject::adjustedPositionRelativeToOffsetParent(const LayoutPoint& startPoint) const
 {
     // If the element is the HTML body element or doesn't have a parent
     // return 0 and stop this algorithm.
     if (isBody() || !parent())
         return LayoutPoint();
 
     LayoutPoint referencePoint = startPoint;
     referencePoint.move(parent()->columnOffset(referencePoint));
 
     // If the offsetParent of the element is null, or is the HTML body element,
     // return the distance between the canvas origin and the left border edge
     // of the element and stop this algorithm.
     Element* element = offsetParent();
     if (!element)
         return referencePoint;
 
     if (const LayoutBoxModelObject* offsetParent = element->layoutBoxModelObject()) {
         if (offsetParent->isBox() && !offsetParent->isBody())
             referencePoint.move(-toLayoutBox(offsetParent)->borderLeft(), -toLayoutBox(offsetParent)->borderTop());
         if (!isOutOfFlowPositioned() || flowThreadContainingBlock()) {
             if (isInFlowPositioned())
-                referencePoint.move(relativePositionOffset());
+                referencePoint.move(offsetForInFlowPosition());
 
             LayoutObject* current;
             for (current = parent(); current != offsetParent && current->parent(); current = current->parent()) {
                 // FIXME: What are we supposed to do inside SVG content?
                 if (!isOutOfFlowPositioned()) {
                     if (current->isBox() && !current->isTableRow())
                         referencePoint.moveBy(toLayoutBox(current)->topLeftLocation());
                     referencePoint.move(current->parent()->columnOffset(referencePoint));
                 }
             }
 
             if (offsetParent->isBox() && offsetParent->isBody() && !offsetParent->isPositioned())
                 referencePoint.moveBy(toLayoutBox(offsetParent)->topLeftLocation());
         }
     }
 
     return referencePoint;
 }
 
 LayoutSize LayoutBoxModelObject::offsetForInFlowPosition() const
 {
-    return isRelPositioned() ? relativePositionOffset() : LayoutSize();
+    if (isRelPositioned())
+        return relativePositionOffset();
+
+    if (isStickyPositioned())
+        return stickyPositionOffset();
+
+    return LayoutSize();
 }
 
 LayoutUnit LayoutBoxModelObject::offsetLeft() const
 {
     // Note that LayoutInline and LayoutBox override this to pass a different
     // startPoint to adjustedPositionRelativeToOffsetParent.
     return adjustedPositionRelativeToOffsetParent(LayoutPoint()).x();
 }
 
 LayoutUnit LayoutBoxModelObject::offsetTop() const
@@ skipping 301 matching lines @@
 const LayoutObject* LayoutBoxModelObject::pushMappingToContainer(const LayoutBoxModelObject* ancestorToStopAt, LayoutGeometryMap& geometryMap) const
 {
     ASSERT(ancestorToStopAt != this);
 
     bool ancestorSkipped;
     LayoutObject* container = this->container(ancestorToStopAt, &ancestorSkipped);
     if (!container)
         return nullptr;
 
     bool isInline = isLayoutInline();
-    bool isFixedPos = !isInline && style()->position() == FixedPosition;
+    bool isViewportConstrained = !isInline && (style()->hasViewportConstrainedPosition());
     bool hasTransform = !isInline && hasLayer() && layer()->transform();
 
     LayoutSize adjustmentForSkippedAncestor;
     if (ancestorSkipped) {
         // There can't be a transform between paintInvalidationContainer and ancestorToStopAt, because transforms create containers, so it should be safe
         // to just subtract the delta between the ancestor and ancestorToStopAt.
         adjustmentForSkippedAncestor = -ancestorToStopAt->offsetFromAncestorContainer(container);
     }
 
     bool offsetDependsOnPoint = false;
     LayoutSize containerOffset = offsetFromContainer(container, LayoutPoint(), &offsetDependsOnPoint);
 
     bool preserve3D = container->style()->preserves3D() || style()->preserves3D();
     if (shouldUseTransformFromContainer(container)) {
         TransformationMatrix t;
         getTransformFromContainer(container, containerOffset, t);
         t.translateRight(adjustmentForSkippedAncestor.width().toFloat(), adjustmentForSkippedAncestor.height().toFloat());
-        geometryMap.push(this, t, preserve3D, offsetDependsOnPoint, isFixedPos, hasTransform);
+        geometryMap.push(this, t, preserve3D, offsetDependsOnPoint, isViewportConstrained, hasTransform);
     } else {
         containerOffset += adjustmentForSkippedAncestor;
-        geometryMap.push(this, containerOffset, preserve3D, offsetDependsOnPoint, isFixedPos, hasTransform);
+        geometryMap.push(this, containerOffset, preserve3D, offsetDependsOnPoint, isViewportConstrained, hasTransform);
     }
 
     return ancestorSkipped ? ancestorToStopAt : container;
 }
 
 void LayoutBoxModelObject::moveChildTo(LayoutBoxModelObject* toBoxModelObject, LayoutObject* child, LayoutObject* beforeChild, bool fullRemoveInsert)
 {
     // We assume that callers have cleared their positioned objects list for child moves (!fullRemoveInsert) so the
     // positioned layoutObject maps don't become stale. It would be too slow to do the map lookup on each call.
     ASSERT(!fullRemoveInsert || !isLayoutBlock() || !toLayoutBlock(this)->hasPositionedObjects());
@@ skipping 47 matching lines @@
     if (rootElementStyle->hasBackground())
         return false;
 
     if (node() != document().firstBodyElement())
         return false;
 
     return true;
 }
 
 } // namespace blink