Start adding ability to observe marker head positions

src/app/buffer-marker.coffee

@@ -6,19 +6,21 @@ module.exports =
 class BufferMarker
   headPosition: null
   tailPosition: null
+  headPositionObservers: null
   stayValid: false
 
   constructor: ({@id, @buffer, range, @stayValid, noTail, reverse}) ->
+    @headPositionObservers = []
     @setRange(range, {noTail, reverse})
 
   setRange: (range, options={}) ->
-    range = @buffer.clipRange(range)
+    range = Range.fromObject(range)
     if options.reverse
-      @tailPosition = range.end unless options.noTail
-      @headPosition = range.start
+      @setTailPosition(range.end) unless options.noTail
+      @setHeadPosition(range.start)
     else
-      @tailPosition = range.start unless options.noTail
-      @headPosition = range.end
+      @setTailPosition(range.start) unless options.noTail
+      @setHeadPosition(range.end)
 
   isReversed: ->
     @tailPosition? and @headPosition.isLessThan(@tailPosition)
@@ -36,6 +38,8 @@ class BufferMarker
   setHeadPosition: (headPosition, options={}) ->
     @headPosition = Point.fromObject(headPosition)
     @headPosition = @buffer.clipPosition(@headPosition) if options.clip ? true
+    observer(@headPosition) for observer in @headPositionObservers
+    @headPosition
 
   setTailPosition: (tailPosition, options={}) ->
     @tailPosition = Point.fromObject(tailPosition)
@@ -47,6 +51,9 @@ class BufferMarker
   getEndPosition: ->
     @getRange().end
 
+  observeHeadPosition: (callback) ->
+    @headPositionObservers.push(callback)
+
   tryToInvalidate: (oldRange) ->
     containsStart = oldRange.containsPoint(@getStartPosition(), exclusive: true)
     containsEnd = oldRange.containsPoint(@getEndPosition(), exclusive: true)
@@ -66,8 +73,8 @@ class BufferMarker
       [@id]
 
   handleBufferChange: (bufferChange) ->
-    @setTailPosition(@updatePosition(@tailPosition, bufferChange, true), clip: false)
     @setHeadPosition(@updatePosition(@headPosition, bufferChange, false), clip: false)
+    @setTailPosition(@updatePosition(@tailPosition, bufferChange, true), clip: false) if @tailPosition
 
   updatePosition: (position, bufferChange, isFirstPoint) ->
     { oldRange, newRange } = bufferChange

src/app/buffer.coffee

@@ -307,6 +307,9 @@ class Buffer
   isMarkerReversed: (id) ->
     @validMarkers[id]?.isReversed()
 
+  observeMarkerHeadPosition: (id, callback) ->
+    @validMarkers[id]?.observeHeadPosition(callback)
+
   getAnchors: -> new Array(@anchors...)
 
   addAnchor: (options) ->

src/app/display-buffer.coffee

@@ -16,6 +16,8 @@ class DisplayBuffer
   tokenizedBuffer: null
   activeFolds: null
   foldsById: null
+  markerScreenPositionObservers: null
+  markerScreenPositions: null
 
   constructor: (@buffer, options={}) ->
     @id = @constructor.idCounter++
@@ -24,6 +26,9 @@ class DisplayBuffer
     @softWrapColumn = options.softWrapColumn ? Infinity
     @activeFolds = {}
     @foldsById = {}
+    @markerScreenPositionObservers = {}
+    @markerScreenPositions = {}
+
     @buildLineMap()
     @tokenizedBuffer.on 'changed', (e) => @handleTokenizedBufferChange(e)
 
@@ -33,13 +38,17 @@ class DisplayBuffer
     @lineMap = new LineMap
     @lineMap.insertAtScreenRow 0, @buildLinesForBufferRows(0, @buffer.getLastRow())
 
+  triggerChanged: (eventProperties) ->
+    @notifyMarkerScreenPositionObservers() unless eventProperties.bufferChange
+    @trigger 'changed', eventProperties
+
   setSoftWrapColumn: (@softWrapColumn) ->
     start = 0
     end = @getLastRow()
     @buildLineMap()
     screenDelta = @getLastRow() - end
     bufferDelta = 0
-    @trigger 'changed', { start, end, screenDelta, bufferDelta }
+    @triggerChanged({ start, end, screenDelta, bufferDelta })
 
   lineForRow: (row) ->
     @lineMap.lineForScreenRow(row)
@@ -95,7 +104,7 @@ class DisplayBuffer
       end = oldScreenRange.end.row
       screenDelta = newScreenRange.end.row - oldScreenRange.end.row
       bufferDelta = 0
-      @trigger 'changed', { start, end, screenDelta, bufferDelta }
+      @triggerChanged({ start, end, screenDelta, bufferDelta })
 
     fold
 
@@ -124,7 +133,8 @@ class DisplayBuffer
       screenDelta = newScreenRange.end.row - oldScreenRange.end.row
       bufferDelta = 0
 
-      @trigger 'changed', { start, end, screenDelta, bufferDelta }
+      @notifyMarkerScreenPositionObservers()
+      @triggerChanged({ start, end, screenDelta, bufferDelta })
 
   destroyFoldsContainingBufferRow: (bufferRow) ->
     for row, folds of @activeFolds
@@ -225,7 +235,7 @@ class DisplayBuffer
     @lineMap.replaceScreenRows(start, end, newScreenLines)
     screenDelta = @lastScreenRowForBufferRow(tokenizedBufferEnd + tokenizedBufferDelta) - end
 
-    @trigger 'changed', { start, end, screenDelta, bufferDelta, bufferChange }
+    @triggerChanged({ start, end, screenDelta, bufferDelta, bufferChange })
 
   buildLineForBufferRow: (bufferRow) ->
     @buildLinesForBufferRows(bufferRow, bufferRow)
@@ -341,6 +351,24 @@ class DisplayBuffer
   isMarkerReversed: (id) ->
     @buffer.isMarkerReversed(id)
 
+  observeMarkerHeadScreenPosition: (id, callback) ->
+    @markerScreenPositionObservers[id] ?= { head: [], tail: [] }
+    @cacheMarkerScreenPositions(id) unless @markerScreenPositions[id]
+    @markerScreenPositionObservers[id].head.push(callback)
+    @buffer.observeMarkerHeadPosition id, (bufferPosition) =>
+      @cacheMarkerScreenPositions(id)
+      callback(@screenPositionForBufferPosition(bufferPosition))
+
+  cacheMarkerScreenPositions: (id) ->
+    @markerScreenPositions[id] = { head: @getMarkerHeadScreenPosition(id), tail: @getMarkerTailScreenPosition }
+
+  notifyMarkerScreenPositionObservers: ->
+    for id, { head } of @markerScreenPositions
+      currentHeadPosition = @getMarkerHeadScreenPosition(id)
+      unless currentHeadPosition.isEqual(head)
+        @cacheMarkerScreenPositions(id)
+        observer(currentHeadPosition) for observer in @markerScreenPositionObservers[id].head
+
   destroy: ->
     @tokenizedBuffer.destroy()
 

src/app/edit-session.coffee

@@ -440,11 +440,20 @@ class EditSession
   markBufferPosition: (args...) ->
     @displayBuffer.markBufferPosition(args...)
 
-  getMarkerBufferRange: (marker) ->
-    @displayBuffer.getMarkerBufferRange(marker)
+  getMarkerBufferRange: (args...) ->
+    @displayBuffer.getMarkerBufferRange(args...)
 
-  getMarkerScreenRange: (marker) ->
-    @displayBuffer.getMarkerScreenRange(marker)
+  getMarkerScreenRange: (args...) ->
+    @displayBuffer.getMarkerScreenRange(args...)
+
+  getMarkerBufferPosition: (args...) ->
+    @displayBuffer.getMarkerBufferPosition(args...)
+
+  getMarkerHeadBufferPosition: (args...) ->
+    @displayBuffer.getMarkerHeadBufferPosition(args...)
+
+  getMarkerTailBufferPosition: (args...) ->
+    @displayBuffer.getMarkerTailBufferPosition(args...)
 
   addAnchor: (options={}) ->
     anchor = @buffer.addAnchor(_.extend({editSession: this}, options))