From 2c035f50728f5c8b0d0b993148dc8f731e6d2332 Mon Sep 17 00:00:00 2001
From: Andreas Kling <awesomekling@gmail.com>
Date: Sun, 13 Oct 2019 12:49:43 +0200
Subject: [PATCH] LibHTML: Split layout invalidation into style and layout
 invalidation

When style is invalidated (for example when an external stylesheet
finishes loading) we delete the whole layout tree and build a new one.
This is necessary since the new style information may result in a
different layout tree.

When layout is invalidated (window resized, image dimensions learned,
etc..) we keep the existing layout tree but run the layout algorithm
once again.

There's obviously lots of room for improvement here. :^)
---
 Libraries/LibHTML/DOM/Document.cpp        | 9 ++++++++-
 Libraries/LibHTML/DOM/Document.h          | 1 +
 Libraries/LibHTML/DOM/HTMLLinkElement.cpp | 2 +-
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/Libraries/LibHTML/DOM/Document.cpp b/Libraries/LibHTML/DOM/Document.cpp
index 9b0cde1ad0..492b1b231a 100644
--- a/Libraries/LibHTML/DOM/Document.cpp
+++ b/Libraries/LibHTML/DOM/Document.cpp
@@ -153,10 +153,17 @@ URL Document::complete_url(const String& string) const
 
 void Document::layout()
 {
-    m_layout_root = create_layout_tree(style_resolver(), nullptr);
+    if (!m_layout_root)
+        m_layout_root = create_layout_tree(style_resolver(), nullptr);
     m_layout_root->layout();
 }
 
+void Document::invalidate_style()
+{
+    m_layout_root = nullptr;
+    invalidate_layout();
+}
+
 void Document::invalidate_layout()
 {
     layout();
diff --git a/Libraries/LibHTML/DOM/Document.h b/Libraries/LibHTML/DOM/Document.h
index 0566298b59..148d577417 100644
--- a/Libraries/LibHTML/DOM/Document.h
+++ b/Libraries/LibHTML/DOM/Document.h
@@ -67,6 +67,7 @@ public:
 
     void layout();
 
+    void invalidate_style();
     void invalidate_layout();
     Function<void()> on_invalidate_layout;
 
diff --git a/Libraries/LibHTML/DOM/HTMLLinkElement.cpp b/Libraries/LibHTML/DOM/HTMLLinkElement.cpp
index 94a955731f..194427ae6f 100644
--- a/Libraries/LibHTML/DOM/HTMLLinkElement.cpp
+++ b/Libraries/LibHTML/DOM/HTMLLinkElement.cpp
@@ -29,7 +29,7 @@ void HTMLLinkElement::inserted_into(Node&)
                 return;
             }
             document().add_sheet(*sheet);
-            document().invalidate_layout();
+            document().invalidate_style();
         });
     }
 }