When buffer or display-buffer change, update the position of all anchors on EditSession.

Cursors and selections no longer need to handle buffer/display-buffer changes directly. They register anchors with the EditSession, and subscribe to changes in their position instead. This opens up the anchor facility for use by extensions that want to track the screen position of a point in the buffer as the buffer and display buffer change.

src/app/anchor.coffee

@@ -1,4 +1,6 @@
 Point = require 'point'
+EventEmitter = require 'event-emitter'
+_ = require 'underscore'
 
 module.exports =
 class Anchor
@@ -21,7 +23,7 @@ class Anchor
       newColumn = position.column
       newRow += position.row - oldRange.end.row
 
-    @setBufferPosition [newRow, newColumn]
+    @setBufferPosition([newRow, newColumn], bufferChange: true)
 
   getBufferPosition: ->
     @bufferPosition
@@ -36,6 +38,7 @@ class Anchor
     @screenPosition
 
   setScreenPosition: (position, options={}) ->
+    previousScreenPosition = @screenPosition
     @screenPosition = Point.fromObject(position)
     clip = options.clip ? true
     assignBufferPosition = options.assignBufferPosition ? true
@@ -46,7 +49,11 @@ class Anchor
     Object.freeze @screenPosition
     Object.freeze @bufferPosition
 
-  refreshScreenPosition: (options) ->
-    screenPosition = @editSession.screenPositionForBufferPosition(@bufferPosition, options)
-    @setScreenPosition(screenPosition, clip: false, assignBufferPosition: false)
+    unless @screenPosition.isEqual(previousScreenPosition)
+      @trigger 'change-screen-position', @screenPosition, bufferChange: options.bufferChange
 
+  refreshScreenPosition: (options={}) ->
+    screenPosition = @editSession.screenPositionForBufferPosition(@bufferPosition, options)
+    @setScreenPosition(screenPosition, bufferChange: options.bufferChange, clip: false, assignBufferPosition: false)
+
+_.extend(Anchor.prototype, EventEmitter)

src/app/cursor.coffee

@@ -13,6 +13,7 @@ class Cursor
 
   constructor: ({@editSession, screenPosition, bufferPosition}) ->
     @anchor = @editSession.addAnchor()
+    @anchor.on 'change-screen-position', (args...) => @trigger 'change-screen-position', args...
     @setScreenPosition(screenPosition) if screenPosition
     @setBufferPosition(bufferPosition) if bufferPosition
 
@@ -22,19 +23,17 @@ class Cursor
     @trigger 'destroy'
 
   setScreenPosition: (screenPosition, options) ->
-    @anchor.setScreenPosition(screenPosition, options)
     @goalColumn = null
     @clearSelection()
-    @trigger 'change-screen-position', @getScreenPosition(), bufferChange: false
+    @anchor.setScreenPosition(screenPosition, options)
 
   getScreenPosition: ->
     @anchor.getScreenPosition()
 
   setBufferPosition: (bufferPosition, options) ->
-    @anchor.setBufferPosition(bufferPosition, options)
     @goalColumn = null
     @clearSelection()
-    @trigger 'change-screen-position', @getScreenPosition(), bufferChange: false
+    @anchor.setBufferPosition(bufferPosition, options)
 
   getBufferPosition: ->
     @anchor.getBufferPosition()
@@ -54,11 +53,6 @@ class Cursor
 
   refreshScreenPosition: ->
     @anchor.refreshScreenPosition()
-    @trigger 'change-screen-position', @getScreenPosition(), bufferChange: false
-
-  handleBufferChange: (e) ->
-    @anchor.handleBufferChange(e)
-    @trigger 'change-screen-position', @getScreenPosition(), bufferChange: true
 
   moveUp: ->
     { row, column } = @getScreenPosition()

src/app/edit-session.coffee

@@ -39,12 +39,13 @@ class EditSession
     @addCursorAtScreenPosition([0, 0])
 
     @buffer.on "change.edit-session-#{@id}", (e) =>
-      for selection in @getSelections()
-        selection.handleBufferChange(e)
+      anchor.handleBufferChange(e) for anchor in @getAnchors()
+      @mergeCursors()
 
     @displayBuffer.on "change.edit-session-#{@id}", (e) =>
       @trigger 'screen-lines-change', e
-      @moveCursors (cursor) -> cursor.refreshScreenPosition() unless e.bufferChanged
+      unless e.bufferChanged
+        anchor.refreshScreenPosition() for anchor in @getAnchors()
 
   destroy: ->
     @buffer.off ".edit-session-#{@id}"
@@ -230,6 +231,9 @@ class EditSession
     fn(selection) for selection in selections
     @buffer.endUndoBatch(@getSelectedBufferRanges())
 
+  getAnchors: ->
+    new Array(@anchors...)
+
   addAnchor: ->
     anchor = new Anchor(this)
     @anchors.push(anchor)

src/app/point.coffee

@@ -56,6 +56,7 @@ class Point
         0
 
   isEqual: (other) ->
+    return false unless other
     other = Point.fromObject(other)
     @row == other.row and @column == other.column
 

src/app/selection.coffee

@@ -211,11 +211,6 @@ class Selection
   autoOutdent: ->
     @editSession.autoOutdentBufferRow(@cursor.getBufferRow())
 
-  handleBufferChange: (e) ->
-    @modifyScreenRange =>
-      @anchor?.handleBufferChange(e)
-      @cursor.handleBufferChange(e)
-
   modifySelection: (fn) ->
     @retainSelection = true
     @view?.retainSelection = true