Cache the overlay dimensions in the presenter

src/overlay-manager.coffee

@@ -1,30 +1,86 @@
 module.exports =
 class OverlayManager
   constructor: (@presenter, @container) ->
-    @overlayNodesById = {}
+    @overlaysById = {}
 
   render: (state) ->
-    for decorationId, {pixelPosition, item} of state.content.overlays
-      @renderOverlay(state, decorationId, item, pixelPosition)
+    editorDimensionsHaveChanged = !@editorDimensionsAreEqual(state)
 
-    for id, overlayNode of @overlayNodesById
+    for decorationId, overlay of state.content.overlays
+      overlayHasChanged = not @overlayStateIsEqual(decorationId, overlay)
+      if editorDimensionsHaveChanged or overlayHasChanged
+        @renderOverlay(state, decorationId, overlay)
+        @cacheOverlayState(decorationId, overlay)
+
+    for id, {overlayNode} of @overlaysById
       unless state.content.overlays.hasOwnProperty(id)
-        delete @overlayNodesById[id]
+        delete @overlaysById[id]
         overlayNode.remove()
 
-    return
+    @cacheEditorDimensions(state)
 
-  renderOverlay: (state, decorationId, item, pixelPosition) ->
+  overlayStateIsEqual: (decorationId, overlay) ->
+    return false unless @overlaysById[decorationId]?
+    @overlaysById[decorationId].itemWidth is overlay.itemWidth and
+      @overlaysById[decorationId].itemHeight is overlay.itemHeight and
+      @overlaysById[decorationId].contentMargin is overlay.contentMargin and
+      @overlaysById[decorationId].pixelPosition?.top is overlay.pixelPosition?.top and
+      @overlaysById[decorationId].pixelPosition?.left is overlay.pixelPosition?.left
+
+  cacheOverlayState: (decorationId, overlay) ->
+    return unless @overlaysById[decorationId]?
+    @overlaysById[decorationId].itemWidth = overlay.itemWidth
+    @overlaysById[decorationId].itemHeight = overlay.itemHeight
+    @overlaysById[decorationId].contentMargin = overlay.contentMargin
+    @overlaysById[decorationId].pixelPosition = overlay.pixelPosition
+
+  cacheEditorDimensions: (state) ->
+    @cachedEditorDimensions =
+      lineHeight: @presenter.lineHeight
+      contentFrameWidth: @presenter.contentFrameWidth
+      editorTop: @presenter.boundingClientRect?.top
+      editorLeft: @presenter.boundingClientRect?.left
+      editorWidth: @presenter.boundingClientRect?.width
+      windowWidth: @presenter.windowWidth
+      windowHeight: @presenter.windowHeight
+      scrollTop: state.content.scrollTop
+      scrollLeft: state.content.scrollLeft
+
+  editorDimensionsAreEqual: (state) ->
+    return false unless @cachedEditorDimensions?
+    @cachedEditorDimensions.lineHeight is @presenter.lineHeight and
+      @cachedEditorDimensions.contentFrameWidth is @presenter.contentFrameWidth and
+      @cachedEditorDimensions.editorTop is @presenter.boundingClientRect?.top and
+      @cachedEditorDimensions.editorLeft is @presenter.boundingClientRect?.left and
+      @cachedEditorDimensions.editorWidth is @presenter.boundingClientRect?.width and
+      @cachedEditorDimensions.windowWidth is @presenter.windowWidth and
+      @cachedEditorDimensions.windowHeight is @presenter.windowHeight and
+      @cachedEditorDimensions.scrollTop is state.content.scrollTop and
+      @cachedEditorDimensions.scrollLeft is state.content.scrollLeft
+
+  measureOverlays: ->
+    for decorationId, {item} of @overlaysById
+      @measureOverlay(decorationId, item)
+
+  measureOverlay: (decorationId, item) ->
+    contentMargin = parseInt(getComputedStyle(item)['margin-left']) ? 0
+    @presenter.setOverlayDimensions(decorationId, item.offsetWidth, item.offsetHeight, contentMargin)
+
+  renderOverlay: (state, decorationId, {item, pixelPosition}) ->
     item = atom.views.getView(item)
-    unless overlayNode = @overlayNodesById[decorationId]
-      overlayNode = @overlayNodesById[decorationId] = document.createElement('atom-overlay')
+    overlay = @overlaysById[decorationId]
+    unless overlayNode = overlay?.overlayNode
+      overlayNode = document.createElement('atom-overlay')
       overlayNode.appendChild(item)
       @container.appendChild(overlayNode)
+      @overlaysById[decorationId] = overlay = {overlayNode, item}
 
-    itemWidth = item.offsetWidth
-    itemHeight = item.offsetHeight
-    contentMargin = parseInt(getComputedStyle(item)['margin-left']) ? 0
+    overlayDimensions = @presenter.getOverlayDimensions(decorationId)
+    unless overlayDimensions?.itemWidth?
+      @measureOverlay(decorationId, item)
+      overlayDimensions = @presenter.getOverlayDimensions(decorationId)
 
+    {itemWidth, itemHeight, contentMargin} = overlayDimensions
     {scrollTop, scrollLeft} = state.content
 
     editorBounds = @presenter.boundingClientRect