1 files changed, 88 insertions, 0 deletions
diff --git a/atom/packages/vim-mode/lib/scroll.coffee b/atom/packages/vim-mode/lib/scroll.coffee
new file mode 100644
index 0000000..1bc1258
--- /dev/null
+++ b/atom/packages/vim-mode/lib/scroll.coffee
@@ -0,0 +1,88 @@
+class Scroll
+  isComplete: -> true
+  isRecordable: -> false
+  constructor: (@editorElement) ->
+    @scrolloff = 2 # atom default
+    @editor = @editorElement.getModel()
+    @rows =
+      first: @editorElement.getFirstVisibleScreenRow()
+      last: @editorElement.getLastVisibleScreenRow()
+      final: @editor.getLastScreenRow()
+
+class ScrollDown extends Scroll
+  execute: (count=1) ->
+    @keepCursorOnScreen(count)
+    @scrollUp(count)
+
+  keepCursorOnScreen: (count) ->
+    {row, column} = @editor.getCursorScreenPosition()
+    firstScreenRow = @rows.first + @scrolloff + 1
+    if row - count <= firstScreenRow
+      @editor.setCursorScreenPosition([firstScreenRow + count, column])
+
+  scrollUp: (count) ->
+    lastScreenRow = @rows.last - @scrolloff
+    @editor.scrollToScreenPosition([lastScreenRow + count, 0])
+
+class ScrollUp extends Scroll
+  execute: (count=1) ->
+    @keepCursorOnScreen(count)
+    @scrollDown(count)
+
+  keepCursorOnScreen: (count) ->
+    {row, column} = @editor.getCursorScreenPosition()
+    lastScreenRow = @rows.last - @scrolloff - 1
+    if row + count >= lastScreenRow
+      @editor.setCursorScreenPosition([lastScreenRow - count, column])
+
+  scrollDown: (count) ->
+    firstScreenRow = @rows.first + @scrolloff
+    @editor.scrollToScreenPosition([firstScreenRow - count, 0])
+
+class ScrollCursor extends Scroll
+  constructor: (@editorElement, @opts={}) ->
+    super
+    cursor = @editor.getCursorScreenPosition()
+    @pixel = @editorElement.pixelPositionForScreenPosition(cursor).top
+
+class ScrollCursorToTop extends ScrollCursor
+  execute: ->
+    @moveToFirstNonBlank() unless @opts.leaveCursor
+    @scrollUp()
+
+  scrollUp: ->
+    return if @rows.last is @rows.final
+    @pixel -= (@editor.getLineHeightInPixels() * @scrolloff)
+    @editor.setScrollTop(@pixel)
+
+  moveToFirstNonBlank: ->
+    @editor.moveToFirstCharacterOfLine()
+
+class ScrollCursorToMiddle extends ScrollCursor
+  execute: ->
+    @moveToFirstNonBlank() unless @opts.leaveCursor
+    @scrollMiddle()
+
+  scrollMiddle: ->
+    @pixel -= (@editor.getHeight() / 2)
+    @editor.setScrollTop(@pixel)
+
+  moveToFirstNonBlank: ->
+    @editor.moveToFirstCharacterOfLine()
+
+class ScrollCursorToBottom extends ScrollCursor
+  execute: ->
+    @moveToFirstNonBlank() unless @opts.leaveCursor
+    @scrollDown()
+
+  scrollDown: ->
+    return if @rows.first is 0
+    offset = (@editor.getLineHeightInPixels() * (@scrolloff + 1))
+    @pixel -= (@editor.getHeight() - offset)
+    @editor.setScrollTop(@pixel)
+
+  moveToFirstNonBlank: ->
+    @editor.moveToFirstCharacterOfLine()
+
+module.exports = {ScrollDown, ScrollUp, ScrollCursorToTop, ScrollCursorToMiddle,
+  ScrollCursorToBottom}