Adapt and reland old position sticky implementation

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

 /*
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 20 matching lines @@
 #include "core/paint/PaintLayer.h"
 #include "platform/geometry/TransformState.h"
 #include "wtf/TemporaryChange.h"
 
 namespace blink {
 
 LayoutGeometryMap::LayoutGeometryMap(MapCoordinatesFlags flags)
     : m_insertionPosition(kNotFound)
     , m_nonUniformStepsCount(0)
     , m_transformedStepsCount(0)
-    , m_fixedStepsCount(0)
+    , m_viewportConstrainedStepsCount(0)
     , m_mapCoordinatesFlags(flags)
 {
 }
 
 LayoutGeometryMap::~LayoutGeometryMap()
 {
 }
 
 void LayoutGeometryMap::mapToContainer(TransformState& transformState, const LayoutBoxModelObject* container) const
 {
     // If the mapping includes something like columns, we have to go via layoutObjects.
     if (hasNonUniformStep()) {
         m_mapping.last().m_layoutObject->mapLocalToContainer(container, transformState, ApplyContainerFlip | m_mapCoordinatesFlags);
         transformState.flatten();
         return;
     }
 
     bool inFixed = false;
 #if ENABLE(ASSERT)
     bool foundContainer = !container || (m_mapping.size() && m_mapping[0].m_layoutObject == container);
 #endif
 
     for (int i = m_mapping.size() - 1; i >= 0; --i) {
         const LayoutGeometryMapStep& currentStep = m_mapping[i];
 
-        // If container is the root LayoutView (step 0) we want to apply its fixed position offset.
+        // If container is the root LayoutView (step 0) we want to apply its viewport constrained position offset.

[chrishtr, 2015/11/04 01:55:18]

Sticky elements are not quite viewport constrained, they are containing scroller
constrained. Doesn't this mean that the changes here are not correct in those
cases?

[flackr, 2015/11/25 20:47:52]

Yes, I rethought this and it seems we can get by with simply passing the sticky
offset. This field can be re-used if and when other cases occur.

         if (i > 0 && currentStep.m_layoutObject == container) {
 #if ENABLE(ASSERT)
             foundContainer = true;
 #endif
             break;
         }
 
-        // If this box has a transform, it acts as a fixed position container
-        // for fixed descendants, which prevents the propagation of 'fixed'
-        // unless the layer itself is also fixed position.
-        if (i && currentStep.m_hasTransform && !currentStep.m_isFixedPosition)
+        // If this box has a transform, it acts as a viewport constrained position container
+        // for viewport constrained descendants, which prevents the propagation of viewport constrained
+        // unless the layer itself is also a viewport constrained position.
+        // TODO(flackr): Verify how fixed and sticky elements should interact with each other.

[chrishtr, 2015/11/04 01:55:18]

Meaning: what should happen with a sticky element below a fixed one?

[flackr, 2015/11/25 20:47:52]

Correct. FWIW I have now tested both of these and they have reasonable behavior
(what you'd expect to happen) under Firefox and this patch matches Firefox's
behavior so I've removed the comment.

+        if (i && currentStep.m_hasTransform && !currentStep.m_isViewportConstrained)
             inFixed = false;
-        else if (currentStep.m_isFixedPosition)
+        else if (currentStep.m_isViewportConstrained)
             inFixed = true;
 
         ASSERT(!i == isTopmostLayoutView(currentStep.m_layoutObject));
 
         if (!i) {
             // A null container indicates mapping through the root LayoutView, so including its transform (the page scale).
             if (!container && currentStep.m_transform)
                 transformState.applyTransform(*currentStep.m_transform.get());
         } else {
             TransformState::TransformAccumulation accumulate = currentStep.m_accumulatingTransform ? TransformState::AccumulateTransform : TransformState::FlattenTransform;
             if (currentStep.m_transform)
                 transformState.applyTransform(*currentStep.m_transform.get(), accumulate);
             else
                 transformState.move(currentStep.m_offset.width(), currentStep.m_offset.height(), accumulate);
         }
 
-        if (inFixed && !currentStep.m_offsetForFixedPosition.isZero()) {
+        if (inFixed && !currentStep.m_offsetForViewportConstrained.isZero()) {
             ASSERT(currentStep.m_layoutObject->isLayoutView());
-            transformState.move(currentStep.m_offsetForFixedPosition);
+            transformState.move(currentStep.m_offsetForViewportConstrained);
         }
     }
 
     ASSERT(foundContainer);
     transformState.flatten();
 }
 
 FloatPoint LayoutGeometryMap::mapToContainer(const FloatPoint& p, const LayoutBoxModelObject* container) const
 {
     FloatPoint result;
 
-    if (!hasFixedPositionStep() && !hasTransformStep() && !hasNonUniformStep() && (!container || (m_mapping.size() && container == m_mapping[0].m_layoutObject))) {
+    if (!hasViewportConstrainedStep() && !hasTransformStep() && !hasNonUniformStep() && (!container || (m_mapping.size() && container == m_mapping[0].m_layoutObject))) {
         result = p + m_accumulatedOffset;
     } else {
         TransformState transformState(TransformState::ApplyTransformDirection, p);
         mapToContainer(transformState, container);
         result = transformState.lastPlanarPoint();
     }
 
 #if ENABLE(ASSERT)
     if (m_mapping.size() > 0) {
         const LayoutObject* lastLayoutObject = m_mapping.last().m_layoutObject;
@@ skipping 27 matching lines @@
             fprintf(stderr, " hasTransform");
         fprintf(stderr, "\n");
     }
 }
 #endif
 
 FloatQuad LayoutGeometryMap::mapToContainer(const FloatRect& rect, const LayoutBoxModelObject* container) const
 {
     FloatQuad result;
 
-    if (!hasFixedPositionStep() && !hasTransformStep() && !hasNonUniformStep() && (!container || (m_mapping.size() && container == m_mapping[0].m_layoutObject))) {
+    if (!hasViewportConstrainedStep() && !hasTransformStep() && !hasNonUniformStep() && (!container || (m_mapping.size() && container == m_mapping[0].m_layoutObject))) {
         result = rect;
         result.move(m_accumulatedOffset);
     } else {
         TransformState transformState(TransformState::ApplyTransformDirection, rect.center(), rect);
         mapToContainer(transformState, container);
         result = transformState.lastPlanarQuad();
     }
 
 #if ENABLE(ASSERT)
     if (m_mapping.size() > 0) {
@@ skipping 64 matching lines @@
         layer->convertToLayerCoords(ancestorLayer, layerOffset);
 
         // The LayoutView must be pushed first.
         if (!m_mapping.size()) {
             ASSERT(ancestorLayer->layoutObject()->isLayoutView());
             pushMappingsToAncestor(ancestorLayer->layoutObject(), 0);
         }
 
         TemporaryChange<size_t> positionChange(m_insertionPosition, m_mapping.size());
         bool accumulatingTransform = layer->layoutObject()->style()->preserves3D() || ancestorLayer->layoutObject()->style()->preserves3D();
-        push(layoutObject, toLayoutSize(layerOffset), accumulatingTransform, /*isNonUniform*/ false, /*isFixedPosition*/ false, /*hasTransform*/ false);
+        push(layoutObject, toLayoutSize(layerOffset), accumulatingTransform, /*isNonUniform*/ false, /*isViewportConstrained*/ false, /*hasTransform*/ false);
         return;
     }
     const LayoutBoxModelObject* ancestorLayoutObject = ancestorLayer ? ancestorLayer->layoutObject() : 0;
     pushMappingsToAncestor(layoutObject, ancestorLayoutObject);
 }
 
-void LayoutGeometryMap::push(const LayoutObject* layoutObject, const LayoutSize& offsetFromContainer, bool accumulatingTransform, bool isNonUniform, bool isFixedPosition, bool hasTransform, LayoutSize offsetForFixedPosition)
+void LayoutGeometryMap::push(const LayoutObject* layoutObject, const LayoutSize& offsetFromContainer, bool accumulatingTransform, bool isNonUniform, bool isViewportConstrained, bool hasTransform, LayoutSize offsetForViewportConstrained)
 {
 //    fprintf(stderr, "LayoutGeometryMap::push %p %d,%d isNonUniform=%d\n", layoutObject, offsetFromContainer.width().toInt(), offsetFromContainer.height().toInt(), isNonUniform);
 
     ASSERT(m_insertionPosition != kNotFound);
     ASSERT(!layoutObject->isLayoutView() || !m_insertionPosition || m_mapCoordinatesFlags & TraverseDocumentBoundaries);
-    ASSERT(offsetForFixedPosition.isZero() || layoutObject->isLayoutView());
+    ASSERT(offsetForViewportConstrained.isZero() || layoutObject->isLayoutView());
 
-    m_mapping.insert(m_insertionPosition, LayoutGeometryMapStep(layoutObject, accumulatingTransform, isNonUniform, isFixedPosition, hasTransform));
+    m_mapping.insert(m_insertionPosition, LayoutGeometryMapStep(layoutObject, accumulatingTransform, isNonUniform, isViewportConstrained, hasTransform));
 
     LayoutGeometryMapStep& step = m_mapping[m_insertionPosition];
     step.m_offset = offsetFromContainer;
-    step.m_offsetForFixedPosition = offsetForFixedPosition;
+    step.m_offsetForViewportConstrained = offsetForViewportConstrained;
 
     stepInserted(step);
 }
 
-void LayoutGeometryMap::push(const LayoutObject* layoutObject, const TransformationMatrix& t, bool accumulatingTransform, bool isNonUniform, bool isFixedPosition, bool hasTransform, LayoutSize offsetForFixedPosition)
+void LayoutGeometryMap::push(const LayoutObject* layoutObject, const TransformationMatrix& t, bool accumulatingTransform, bool isNonUniform, bool isViewportConstrained, bool hasTransform, LayoutSize offsetForViewportConstrained)
 {
     ASSERT(m_insertionPosition != kNotFound);
     ASSERT(!layoutObject->isLayoutView() || !m_insertionPosition || m_mapCoordinatesFlags & TraverseDocumentBoundaries);
-    ASSERT(offsetForFixedPosition.isZero() || layoutObject->isLayoutView());
+    ASSERT(offsetForViewportConstrained.isZero() || layoutObject->isLayoutView());
 
-    m_mapping.insert(m_insertionPosition, LayoutGeometryMapStep(layoutObject, accumulatingTransform, isNonUniform, isFixedPosition, hasTransform));
+    m_mapping.insert(m_insertionPosition, LayoutGeometryMapStep(layoutObject, accumulatingTransform, isNonUniform, isViewportConstrained, hasTransform));
 
     LayoutGeometryMapStep& step = m_mapping[m_insertionPosition];
-    step.m_offsetForFixedPosition = offsetForFixedPosition;
+    step.m_offsetForViewportConstrained = offsetForViewportConstrained;
 
     if (!t.isIntegerTranslation())
         step.m_transform = adoptPtr(new TransformationMatrix(t));
     else
         step.m_offset = LayoutSize(t.e(), t.f());
 
     stepInserted(step);
 }
 
 void LayoutGeometryMap::popMappingsToAncestor(const LayoutBoxModelObject* ancestorLayoutObject)
@@ skipping 15 matching lines @@
 void LayoutGeometryMap::stepInserted(const LayoutGeometryMapStep& step)
 {
     m_accumulatedOffset += step.m_offset;
 
     if (step.m_isNonUniform)
         ++m_nonUniformStepsCount;
 
     if (step.m_transform)
         ++m_transformedStepsCount;
 
-    if (step.m_isFixedPosition)
-        ++m_fixedStepsCount;
+    if (step.m_isViewportConstrained)
+        ++m_viewportConstrainedStepsCount;
 }
 
 void LayoutGeometryMap::stepRemoved(const LayoutGeometryMapStep& step)
 {
     m_accumulatedOffset -= step.m_offset;
 
     if (step.m_isNonUniform) {
         ASSERT(m_nonUniformStepsCount);
         --m_nonUniformStepsCount;
     }
 
     if (step.m_transform) {
         ASSERT(m_transformedStepsCount);
         --m_transformedStepsCount;
     }
 
-    if (step.m_isFixedPosition) {
-        ASSERT(m_fixedStepsCount);
-        --m_fixedStepsCount;
+    if (step.m_isViewportConstrained) {
+        ASSERT(m_viewportConstrainedStepsCount);
+        --m_viewportConstrainedStepsCount;
     }
 }
 
 #if ENABLE(ASSERT)
 bool LayoutGeometryMap::isTopmostLayoutView(const LayoutObject* layoutObject) const
 {
     if (!layoutObject->isLayoutView())
         return false;
 
     // If we're not working with multiple LayoutViews, then any view is considered
     // "topmost" (to preserve original behavior).
     if (!(m_mapCoordinatesFlags & TraverseDocumentBoundaries))
         return true;
 
     return layoutObject->frame()->isMainFrame();
 }
 #endif
 
 } // namespace blink