Fix <dialog> centering

Source/core/html/HTMLDialogElement.cpp

 /*
  * Copyright (C) 2012 Google 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
@@ skipping 10 matching lines @@
  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #if ENABLE(DIALOG_ELEMENT)
 #include "HTMLDialogElement.h"
 
 #include "ExceptionCode.h"
-#include "RenderDialog.h"
+#include "FrameView.h"
+#include "RenderBlock.h"
+#include "RenderStyle.h"
+#include "StyleResolver.h"
 
 namespace WebCore {
 
 using namespace HTMLNames;
 
 HTMLDialogElement::HTMLDialogElement(const QualifiedName& tagName, Document* document)
     : HTMLElement(tagName, document)
+    , m_topIsValid(false)
+    , m_top(0)
 {
     ASSERT(hasTagName(dialogTag));
+    setHasCustomStyleCallbacks();
     ScriptWrappable::init(this);
 }
 
 PassRefPtr<HTMLDialogElement> HTMLDialogElement::create(const QualifiedName& tagName, Document* document)
 {
     return adoptRef(new HTMLDialogElement(tagName, document));
 }
 
 void HTMLDialogElement::close(ExceptionCode& ec)
 {
     if (!fastHasAttribute(openAttr)) {
         ec = INVALID_STATE_ERR;
         return;
     }
     setBooleanAttribute(openAttr, false);
     document()->removeFromTopLayer(this);
+    m_topIsValid = false;
+}
+
+static bool needsCenteredPositioning(const RenderStyle* style)
+{
+    return style->position() == AbsolutePosition && style->hasAutoTopAndBottom();
+}
+
+PassRefPtr<RenderStyle> HTMLDialogElement::customStyleForRenderer()
+{
+    RefPtr<RenderStyle> originalStyle = document()->styleResolver()->styleForElement(this);
+    RefPtr<RenderStyle> style = RenderStyle::clone(originalStyle.get());
+
+    // Override top to remain centered after style recalcs.
+    if (needsCenteredPositioning(style.get()) && m_topIsValid)
+        style->setTop(Length(m_top.toInt(), WebCore::Fixed));
+
+    return style.release();
+}
+
+void HTMLDialogElement::positionAndReattach()
+{
+    // Layout because we need to know our ancestors' positions and our own height.
+    document()->updateLayoutIgnorePendingStylesheets();
+
+    RenderBox* box = renderBox();
+    if (!box || !needsCenteredPositioning(box->style()))
+        return;
+
+    // Set up dialog's position to be safe-centered in the viewport.
+    // FIXME: Figure out what to do in vertical writing mode.
+    FrameView* frameView = document()->view();
+    int scrollTop = frameView->scrollOffset().height();
+    FloatPoint absolutePoint(0, scrollTop);
+    int visibleHeight = frameView->visibleContentRect(ScrollableArea::IncludeScrollbars).height();
+    if (box->height() < visibleHeight)
+        absolutePoint.move(0, (visibleHeight - box->height()) / 2);
+    FloatPoint localPoint = box->containingBlock()->absoluteToLocal(absolutePoint);
+
+    m_top = localPoint.y();
+    m_topIsValid = true;
+
+    // FIXME: It's inefficient to reattach here. We could do better by mutating style directly and forcing another layout.
+    reattach();
 }
 
 void HTMLDialogElement::show()
 {
     if (fastHasAttribute(openAttr))
         return;
     setBooleanAttribute(openAttr, true);
+    positionAndReattach();
 }
 
 void HTMLDialogElement::showModal(ExceptionCode& ec)
 {
     if (fastHasAttribute(openAttr) || !inDocument()) {
         ec = INVALID_STATE_ERR;
         return;
     }
+    document()->addToTopLayer(this);
     setBooleanAttribute(openAttr, true);
-    document()->addToTopLayer(this);
+    positionAndReattach();
 }
 
 bool HTMLDialogElement::isPresentationAttribute(const QualifiedName& name) const
 {
     // FIXME: Workaround for <https://bugs.webkit.org/show_bug.cgi?id=91058>: modifying an attribute for which there is an attribute selector
     // in html.css sometimes does not trigger a style recalc.
     if (name == openAttr)
         return true;
 
     return HTMLElement::isPresentationAttribute(name);
 }
 
-RenderObject* HTMLDialogElement::createRenderer(RenderArena* arena, RenderStyle*)
-{
-    return new (arena) RenderDialog(this);
-}
-
 }
 
 #endif