WIP: Start on LineWrapper.displayPositionFromBufferPosition

It takes a row, column from the buffer and converts it to coordinates
that account for line wrapping.

spec/atom/editor-spec.coffee

@@ -50,7 +50,7 @@ describe "Editor", ->
         buffer.insert([1,0], "/*")
         expect(editor.lines.find('.line:eq(2) span:eq(0)')).toMatchSelector '.comment'
 
-    fdescribe "when soft-wrap is enabled", ->
+    describe "when soft-wrap is enabled", ->
       beforeEach ->
         editor.attachToDom()
         editor.width(editor.charWidth * 50)

spec/atom/line-wrapper-spec.coffee

@@ -47,5 +47,17 @@ fdescribe "LineWrapper", ->
         expect(segments[2].lastIndex).toBe 65
         expect(_.pluck(segments[2], 'value').join('')).toBe 'right.push(current);'
 
-  describe "when the buffer changes", ->
-    
+  describe ".displayPositionFromBufferPosition(point)", ->
+    it "returns the position of the indicated row and column on screen, accounting for wrapped lines", ->
+      # no wrap
+      expect(wrapper.displayPositionFromBufferPosition(row: 0, column: 5)).toEqual(row: 0, column: 5)
+
+      # wrap once
+      expect(wrapper.displayPositionFromBufferPosition(row: 3, column: 5)).toEqual(row: 3, column: 5)
+      expect(wrapper.displayPositionFromBufferPosition(row: 3, column: 50)).toEqual(row: 3, column: 50)
+      expect(wrapper.displayPositionFromBufferPosition(row: 3, column: 51)).toEqual(row: 4, column: 0)
+
+      # following a wrap
+      expect(wrapper.displayPositionFromBufferPosition(row: 4, column: 5)).toEqual(row: 5, column: 5)
+
+

src/atom/line-wrapper.coffee

@@ -35,6 +35,7 @@ class LineWrapper
 
     currentSegment = []
     currentSegment.lastIndex = 0
+    currentSegment.textLength = 0
     segments = [currentSegment]
     nextBreak = breakIndices.shift()
     for token in @highlighter.tokensForRow(row)
@@ -50,3 +51,17 @@ class LineWrapper
       currentSegment.textLength += token.value.length
 
     segments
+
+  displayPositionFromBufferPosition: (bufferPosition) ->
+    row = 0
+    for segments in @lines[0...bufferPosition.row]
+      row += segments.length
+
+    column = bufferPosition.column
+    for segment in @lines[bufferPosition.row]
+      break if segment.lastIndex > bufferPosition.column
+      column -= segment.textLength
+      row++
+
+    { row, column }
+