Start on marker interface in DisplayBuffer

spec/app/display-buffer-spec.coffee

@@ -579,3 +579,11 @@ describe "DisplayBuffer", ->
   describe ".maxLineLength()", ->
     it "returns the length of the longest screen line", ->
       expect(displayBuffer.maxLineLength()).toBe 65
+
+  describe "markers", ->
+    it "allows markers to be worked with in terms of both screen and buffer coordinates", ->
+      displayBuffer.foldBufferRow(4)
+      marker1 = displayBuffer.markScreenRange([[5, 4], [5, 10]])
+      marker2 = displayBuffer.markBufferRange([[8, 4], [8, 10]])
+      expect(displayBuffer.getMarkerBufferRange(marker1)).toEqual [[8, 4], [8, 10]]
+      expect(displayBuffer.getMarkerScreenRange(marker2)).toEqual [[5, 4], [5, 10]]

src/app/display-buffer.coffee

@@ -290,6 +290,18 @@ class DisplayBuffer
   rangeForAllLines: ->
     new Range([0, 0], @clipScreenPosition([Infinity, Infinity]))
 
+  markScreenRange: (screenRange) ->
+    @markBufferRange(@bufferRangeForScreenRange(screenRange))
+
+  markBufferRange: (bufferRange) ->
+    @buffer.markRange(bufferRange)
+
+  getMarkerScreenRange: (id) ->
+    @screenRangeForBufferRange(@getMarkerBufferRange(id))
+
+  getMarkerBufferRange: (id) ->
+    @buffer.getMarkerRange(id)
+
   destroy: ->
     @tokenizedBuffer.destroy()