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+[[!meta title="LibCSS Style Sharing"]]
+[[!meta author="Tlsa"]]
+[[!meta date="2014-01-03T15:21:20Z"]]
+
+
+[[!toc]] At the moment NetSurf does
+not share computed styles. Every element on every page has its own
+unique computed style allocated. Computed styles are quite large.
+Consider the following page:
+
+-   <http://git.netsurf-browser.org/netsurf.git/tree/render/layout.c>
+
+It has over twenty thousand element nodes each with its own computed
+style. But there are less than 40 unique computed styles on the page.
+This is a massive waste of memory.
+
+Computed Style Sharing
+----------------------
+
+If different elements can reference the same computed styles, we can
+save a lot of memory.
+
+-   Computed styles will become reference counted.
+-   There are two ways to go about sharing computed styles:
+    1.  Memoising calls to css\_get\_style()
+        -   We'll use selection calbacks to find if node has previous
+            sibling with same element name, classes, etc. If so the
+            style for node can be an extra reference to the computed
+            style of the previous sibling.
+        -   Presentational hint gathering for nodes needs to change such
+            that presentational hints for two nodes can be compared.
+        -   Only shares styles between siblings. Could be extended to
+            share between cousins, etc.
+        -   As well as saving memory, this will make selection faster.
+            -   It will be a big saving in cases where styles can be
+                shared, by bypassing the need to iterate over the
+                applicable selector chains.
+            -   In cases where the styles can't be shared, it will have
+                a relatively small cost.
+
+    2.  Interning computed styles
+        -   Will have a performance cost.
+        -   Much greater scope for sharing computed styles than the
+            above.
+        -   Can even share computed styles between different pages.
+            (NetSurf will be unique in doing that.)
+        -   Fully compatible with the above, so we can do both.
+