*** DO NOT LAND *** Attempt to understand Regions complexity

Source/core/rendering/RenderBoxModelObject.cpp

Index: Source/core/rendering/RenderBoxModelObject.cpp
diff --git a/Source/core/rendering/RenderBoxModelObject.cpp b/Source/core/rendering/RenderBoxModelObject.cpp
index 3b084c5fde5cc73a5bcbaac982dcae77e67fc05c..3868c44409e0721b697b8d2d0a52ba939bb86729 100644
--- a/Source/core/rendering/RenderBoxModelObject.cpp
+++ b/Source/core/rendering/RenderBoxModelObject.cpp
@@ -37,8 +37,6 @@
 #include "core/rendering/RenderInline.h"
 #include "core/rendering/RenderLayer.h"
 #include "core/rendering/RenderLayerCompositor.h"
-#include "core/rendering/RenderNamedFlowThread.h"
-#include "core/rendering/RenderRegion.h"
 #include "core/rendering/RenderView.h"
 #include "core/rendering/style/ShadowList.h"
 #include "platform/geometry/TransformState.h"
@@ -288,17 +286,14 @@ LayoutPoint RenderBoxModelObject::adjustedPositionRelativeToOffsetParent(const L
     if (const RenderBoxModelObject* offsetParent = element->renderBoxModelObject()) {
         if (offsetParent->isBox() && !offsetParent->isBody())
             referencePoint.move(-toRenderBox(offsetParent)->borderLeft(), -toRenderBox(offsetParent)->borderTop());
-        if (!isOutOfFlowPositioned() || flowThreadContainingBlock()) {
+        if (!isOutOfFlowPositioned()) {
             if (isRelPositioned())
                 referencePoint.move(relativePositionOffset());
             else if (isStickyPositioned())
                 referencePoint.move(stickyPositionOffset());
 
-            // CSS regions specification says that region flows should return the body element as their offsetParent.
-            // Since we will bypass the body’s renderer anyway, just end the loop if we encounter a region flow (named flow thread).
-            // See http://dev.w3.org/csswg/css-regions/#cssomview-offset-attributes
             RenderObject* current;
-            for (current = parent(); current != offsetParent && !current->isRenderNamedFlowThread() && current->parent(); current = current->parent()) {
+            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())
@@ -307,11 +302,7 @@ LayoutPoint RenderBoxModelObject::adjustedPositionRelativeToOffsetParent(const L
                 }
             }
 
-            // Compute the offset position for elements inside named flow threads for which the offsetParent was the body.
-            // See https://code.google.com/p/chromium/issues/detail?id=242168
-            if (current->isRenderNamedFlowThread())
-                referencePoint = toRenderNamedFlowThread(current)->adjustedPositionRelativeToOffsetParent(*this, referencePoint);
-            else if (offsetParent->isBox() && offsetParent->isBody() && !offsetParent->isPositioned())
+            if (offsetParent->isBox() && offsetParent->isBody() && !offsetParent->isPositioned())
                 referencePoint.moveBy(toRenderBox(offsetParent)->topLeftLocation());
         }
     }
@@ -385,7 +376,7 @@ LayoutSize RenderBoxModelObject::stickyPositionOffset() const
     RenderLayer* enclosingClippingLayer = layer()->enclosingOverflowClipLayer(ExcludeSelf);
     if (enclosingClippingLayer) {
         RenderBox* enclosingClippingBox = toRenderBox(enclosingClippingLayer->renderer());
-        LayoutRect clipRect = enclosingClippingBox->overflowClipRect(LayoutPoint(), 0); // FIXME: make this work in regions.
+        LayoutRect clipRect = enclosingClippingBox->overflowClipRect(LayoutPoint());
         constrainingRect = enclosingClippingBox->localToContainerQuad(FloatRect(clipRect), view()).boundingBox();
     } else {
         LayoutRect viewportRect = view()->frameView()->viewportConstrainedVisibleContentRect();
@@ -626,7 +617,7 @@ void RenderBoxModelObject::paintFillLayerExtended(const PaintInfo& paintInfo, co
     if (clippedWithLocalScrolling) {
         // Clip to the overflow area.
         RenderBox* thisBox = toRenderBox(this);
-        context->clip(thisBox->overflowClipRect(rect.location(), paintInfo.renderRegion));
+        context->clip(thisBox->overflowClipRect(rect.location()));
 
         // Adjust the paint rect to reflect a scrolled content box with borders at the ends.
         IntSize offset = thisBox->scrolledContentOffset();
@@ -766,7 +757,7 @@ void RenderBoxModelObject::paintFillLayerExtended(const PaintInfo& paintInfo, co
 
         // Now draw the text into the mask. We do this by painting using a special paint phase that signals to
         // InlineTextBoxes that they should just add their contents to the clip.
-        PaintInfo info(context, maskRect, PaintPhaseTextClip, PaintBehaviorForceBlackText, 0, paintInfo.renderRegion);
+        PaintInfo info(context, maskRect, PaintPhaseTextClip, PaintBehaviorForceBlackText, 0);
         context->setCompositeOperation(CompositeSourceOver);
         if (box) {
             RootInlineBox* root = box->root();
@@ -2737,19 +2728,6 @@ void RenderBoxModelObject::mapAbsoluteToLocalPoint(MapCoordinatesFlags mode, Tra
     if (!o)
         return;
 
-    // The point inside a box that's inside a region has its coordinates relative to the region,
-    // not the FlowThread that is its container in the RenderObject tree.
-    if (o->isRenderFlowThread() && isRenderBlock()) {
-        // FIXME: switch to Box instead of Block when we'll have range information for boxes as well, not just for blocks.
-        RenderRegion* startRegion;
-        RenderRegion* ignoredEndRegion;
-        toRenderFlowThread(o)->getRegionRangeForBox(toRenderBlock(this), startRegion, ignoredEndRegion);
-        // If there is no region to use the FlowThread, then there's no region range for the content in that FlowThread.
-        // An API like elementFromPoint might crash without this check.
-        if (startRegion)
-            o = startRegion;
-    }
-
     o->mapAbsoluteToLocalPoint(mode, transformState);
 
     LayoutSize containerOffset = offsetFromContainer(o, LayoutPoint());