Add TextEditorElement::getMaxScrollTop

spec/text-editor-element-spec.coffee

@@ -236,6 +236,27 @@ describe "TextEditorElement", ->
       jasmine.attachToDOM(element)
       expect(element.getDefaultCharacterWidth()).toBeGreaterThan(0)
 
+  describe "::getMaxScrollTop", ->
+    it "returns the maximum scroll top that can be applied to the element", ->
+      editor = atom.workspace.buildTextEditor()
+      editor.setText('1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n12\n13\n14\n15\n16')
+      element = atom.views.getView(editor)
+      element.style.lineHeight = "10px"
+      element.style.width = "200px"
+
+      expect(element.getMaxScrollTop()).toBe(0)
+
+      jasmine.attachToDOM(element)
+
+      element.setHeight(100)
+      expect(element.getMaxScrollTop()).toBe(60)
+
+      element.setHeight(120)
+      expect(element.getMaxScrollTop()).toBe(40)
+
+      element.setHeight(200)
+      expect(element.getMaxScrollTop()).toBe(0)
+
   describe "on TextEditor::setMini", ->
     it "changes the element's 'mini' attribute", ->
       element = new TextEditorElement

src/text-editor-component.coffee

@@ -421,6 +421,9 @@ class TextEditorComponent
   getScrollWidth: ->
     @presenter.getScrollWidth()
 
+  getMaxScrollTop: ->
+    @presenter.getMaxScrollTop()
+
   getVerticalScrollbarWidth: ->
     @presenter.getVerticalScrollbarWidth()
 

src/text-editor-element.coffee

@@ -210,6 +210,12 @@ class TextEditorElement extends HTMLElement
   getDefaultCharacterWidth: ->
     @getModel().getDefaultCharWidth()
 
+  # Extended: Get the maximum scroll top that can be applied to this element.
+  #
+  # Returns a {Number} of pixels.
+  getMaxScrollTop: ->
+    @component?.getMaxScrollTop()
+
   # Extended: Converts a buffer position to a pixel position.
   #
   # * `bufferPosition` An object that represents a buffer position. It can be either

src/text-editor-presenter.coffee

@@ -982,6 +982,13 @@ class TextEditorPresenter
   getScrollWidth: ->
     @scrollWidth
 
+  getMaxScrollTop: ->
+    scrollHeight = @getScrollHeight()
+    clientHeight = @getClientHeight()
+    return 0 unless scrollHeight? and clientHeight?
+
+    scrollHeight - clientHeight
+
   setHorizontalScrollbarHeight: (horizontalScrollbarHeight) ->
     unless @measuredHorizontalScrollbarHeight is horizontalScrollbarHeight
       oldHorizontalScrollbarHeight = @measuredHorizontalScrollbarHeight