Implement shouldComponentUpdate for SelectionsComponent

src/lines-component.coffee

@@ -22,7 +22,7 @@ LinesComponent = React.createClass
         WebkitTransform: "translate3d(#{-scrollLeft}px, #{-scrollTop}px, 0px)"
 
     div {className: 'lines', style},
-      SelectionsComponent({editor, lineHeight}) if @isMounted
+      SelectionsComponent({editor, lineHeight}) if @isMounted()
 
   componentWillMount: ->
     @measuredLines = new WeakSet

src/selection-component.coffee

@@ -6,8 +6,8 @@ SelectionComponent = React.createClass
   displayName: 'SelectionComponent'
 
   render: ->
-    {editor, selection, lineHeight} = @props
-    {start, end} = selection.getScreenRange()
+    {editor, screenRange, lineHeight} = @props
+    {start, end} = screenRange
     rowCount = end.row - start.row + 1
     startPixelPosition = editor.pixelPositionForScreenPosition(start)
     endPixelPosition = editor.pixelPositionForScreenPosition(end)

src/selections-component.coffee

@@ -7,11 +7,37 @@ SelectionsComponent = React.createClass
   displayName: 'SelectionsComponent'
 
   render: ->
+    div className: 'selections', @renderSelections()
+
+  renderSelections: ->
     {editor, lineHeight} = @props
 
-    div className: 'selections',
-      if @isMounted()
-        for selection, index in editor.getSelections()
-          # Rendering artifacts occur on the lines GPU layer if we remove the last selection
-          if index is 0 or (not selection.isEmpty() and editor.selectionIntersectsVisibleRowRange(selection))
-            SelectionComponent({key: selection.id, selection, editor, lineHeight})
+    selectionComponents = []
+    for selectionId, screenRange of @selectionRanges
+      selectionComponents.push(SelectionComponent({key: selectionId, screenRange, editor, lineHeight}))
+    selectionComponents
+
+  componentWillMount: ->
+    @selectionRanges = {}
+
+  shouldComponentUpdate: ->
+    {editor} = @props
+    oldSelectionRanges = @selectionRanges
+    newSelectionRanges = {}
+    @selectionRanges = newSelectionRanges
+
+    for selection, index in editor.getSelections()
+      # Rendering artifacts occur on the lines GPU layer if we remove the last selection
+      if index is 0 or (not selection.isEmpty() and editor.selectionIntersectsVisibleRowRange(selection))
+        newSelectionRanges[selection.id] = selection.getScreenRange()
+
+    for id, range of newSelectionRanges
+      if oldSelectionRanges.hasOwnProperty(id)
+        return true unless range.isEqual(oldSelectionRanges[id])
+      else
+        return true
+
+    for id of oldSelectionRanges
+      return true unless newSelectionRanges.hasOwnProperty(id)
+
+    false