Never use more than 3 divs to render a selection

This should hopefully improve performance for large selections.

spec/atom/selection-spec.coffee

@@ -56,8 +56,8 @@ describe "Selection", ->
         expect(region2.width()).toBe(25 * charWidth)
 
     describe "when the selection spans more than 2 lines", ->
-      it "covers the selection's range with a region for each line", ->
-        selection.setRange(new Range({row: 2, column: 7}, {row: 4, column: 25}))
+      it "covers the selection's range with 3 regions", ->
+        selection.setRange(new Range({row: 2, column: 7}, {row: 6, column: 25}))
 
         expect(selection.regions.length).toBe 3
 
@@ -70,11 +70,11 @@ describe "Selection", ->
         region2 = selection.regions[1]
         expect(region2.position().top).toBe(3 * lineHeight)
         expect(region2.position().left).toBe(0)
-        expect(region2.height()).toBe lineHeight
+        expect(region2.height()).toBe(3 * lineHeight)
         expect(region2.width()).toBe(editor.width())
 
         region3 = selection.regions[2]
-        expect(region3.position().top).toBe(4 * lineHeight)
+        expect(region3.position().top).toBe(6 * lineHeight)
         expect(region3.position().left).toBe(0)
         expect(region3.height()).toBe lineHeight
         expect(region3.width()).toBe(25 * charWidth)

src/atom/editor.coffee

@@ -54,7 +54,7 @@ class Editor extends Template
       @on 'newline', =>  @insertNewline()
       @on 'backspace', => @backspace()
       @on 'delete', => @delete()
-      @on 'copy', => @copyText()
+      @on 'copy', => @copySelection()
 
 
     buildCursorAndSelection: ->
@@ -192,5 +192,5 @@ class Editor extends Template
     insertNewline: -> @selection.insertNewline()
     backspace: -> @selection.backspace()
     delete: -> @selection.delete()
-    copySelection: -> @selection().copy()
+    copySelection: -> @selection.copy()
 

src/atom/selection.coffee

@@ -34,26 +34,22 @@ class Selection extends Template
 
       range = @getRange()
       return if range.isEmpty()
-      for row in [range.start.row..range.end.row]
-        start =
-          if row == range.start.row
-            range.start
-          else
-            { row: row, column: 0 }
 
-        end =
-          if row == range.end.row
-            range.end
-          else
-            null
+      rowSpan = range.end.row - range.start.row
 
-        @appendRegion(start, end)
+      if rowSpan == 0
+        @appendRegion(1, range.start, range.end)
+      else
+        @appendRegion(1, range.start, null)
+        if rowSpan > 1
+          @appendRegion(rowSpan - 1, { row: range.start.row + 1, column: 0}, null)
+        @appendRegion(1, { row: range.end.row, column: 0 }, range.end)
 
-    appendRegion: (start, end) ->
+    appendRegion: (rows, start, end) ->
       { lineHeight, charWidth } = @editor
       top = start.row * lineHeight
       left = start.column * charWidth
-      height = lineHeight
+      height = lineHeight * rows
       width = if end
         end.column * charWidth - left
       else