Make presenter respond to external changes to model's first visible screen row

spec/text-editor-spec.coffee

@@ -4784,6 +4784,71 @@ describe "TextEditor", ->
       editor.selectPageUp()
       expect(editor.getSelectedBufferRanges()).toEqual [[[0, 0], [12, 2]]]
 
+  describe "::setFirstVisibleScreenRow() and ::getFirstVisibleScreenRow()", ->
+    beforeEach ->
+      line = Array(9).join('0123456789')
+      editor.setText([1..100].map(-> line).join('\n'))
+      expect(editor.getLineCount()).toBe 100
+      expect(editor.lineTextForBufferRow(0).length).toBe 80
+
+    describe "when the editor doesn't have a height and lineHeightInPixels", ->
+      it "does not affect the editor's visible row range", ->
+        expect(editor.getVisibleRowRange()).toBeNull()
+
+        editor.setFirstVisibleScreenRow(1)
+        expect(editor.getFirstVisibleScreenRow()).toEqual 1
+
+        editor.setFirstVisibleScreenRow(3)
+        expect(editor.getFirstVisibleScreenRow()).toEqual 3
+
+        expect(editor.getVisibleRowRange()).toBeNull()
+
+    describe "when the editor has a height and lineHeightInPixels", ->
+      beforeEach ->
+        atom.config.set('editor.scrollPastEnd', true)
+        editor.setHeight(100, true)
+        editor.setLineHeightInPixels(10)
+
+      it "updates the editor's visible row range", ->
+        editor.setFirstVisibleScreenRow(2)
+        expect(editor.getFirstVisibleScreenRow()).toEqual 2
+        expect(editor.getVisibleRowRange()).toEqual [2, 12]
+
+      it "notifies ::onDidChangeFirstVisibleScreenRow observers", ->
+        changeCount = 0
+        editor.onDidChangeFirstVisibleScreenRow -> changeCount++
+
+        editor.setFirstVisibleScreenRow(2)
+        expect(changeCount).toBe 1
+
+        editor.setFirstVisibleScreenRow(2)
+        expect(changeCount).toBe 1
+
+        editor.setFirstVisibleScreenRow(3)
+        expect(changeCount).toBe 2
+
+      it "ensures that the top row is less than the buffer's line count", ->
+        editor.setFirstVisibleScreenRow(102)
+        expect(editor.getFirstVisibleScreenRow()).toEqual 99
+        expect(editor.getVisibleRowRange()).toEqual [99, 99]
+
+      it "ensures that the left column is less than the length of the longest screen line", ->
+        editor.setFirstVisibleScreenRow(10)
+        expect(editor.getFirstVisibleScreenRow()).toEqual 10
+
+        editor.setText("\n\n\n")
+
+        editor.setFirstVisibleScreenRow(10)
+        expect(editor.getFirstVisibleScreenRow()).toEqual 3
+
+      describe "when the 'editor.scrollPastEnd' option is set to false", ->
+        it "ensures that the bottom row is less than the buffer's line count", ->
+          atom.config.set('editor.scrollPastEnd', false)
+
+          editor.setFirstVisibleScreenRow(95)
+          expect(editor.getFirstVisibleScreenRow()).toEqual 89
+          expect(editor.getVisibleRowRange()).toEqual [89, 99]
+
   describe '.get/setPlaceholderText()', ->
     it 'can be created with placeholderText', ->
       newEditor = atom.workspace.buildTextEditor(

src/text-editor-presenter.coffee

@@ -213,6 +213,7 @@ class TextEditorPresenter
     @disposables.add @model.onDidAddDecoration(@didAddDecoration.bind(this))
     @disposables.add @model.onDidAddCursor(@didAddCursor.bind(this))
     @disposables.add @model.onDidRequestAutoscroll(@requestAutoscroll.bind(this))
+    @disposables.add @model.onDidChangeFirstVisibleScreenRow(@didChangeFirstVisibleScreenRow.bind(this))
     @observeDecoration(decoration) for decoration in @model.getDecorations()
     @observeCursor(cursor) for cursor in @model.getCursors()
     @disposables.add @model.onDidAddGutter(@didAddGutter.bind(this))
@@ -776,7 +777,7 @@ class TextEditorPresenter
     if scrollTop isnt @realScrollTop and not Number.isNaN(scrollTop)
       @realScrollTop = scrollTop
       @scrollTop = Math.round(scrollTop)
-      @model.setFirstVisibleScreenRow(Math.round(@scrollTop / @lineHeight))
+      @model.setFirstVisibleScreenRow(Math.round(@scrollTop / @lineHeight), true)
 
       @updateStartRow()
       @updateEndRow()
@@ -1539,6 +1540,9 @@ class TextEditorPresenter
 
     @emitDidUpdateState()
 
+  didChangeFirstVisibleScreenRow: (screenRow) ->
+    @updateScrollTop(screenRow * @lineHeight)
+
   getVerticalScrollMarginInPixels: ->
     Math.round(@model.getVerticalScrollMargin() * @lineHeight)
 

src/text-editor.coffee

@@ -448,6 +448,9 @@ class TextEditor extends Model
   onDidChangeCharacterWidths: (callback) ->
     @displayBuffer.onDidChangeCharacterWidths(callback)
 
+  onDidChangeFirstVisibleScreenRow: (callback, fromView) ->
+    @emitter.on 'did-change-first-visible-screen-row', callback
+
   onDidChangeScrollTop: (callback) ->
     Grim.deprecate("This is now a view method. Call TextEditorElement::onDidChangeScrollTop instead.")
 
@@ -3088,13 +3091,27 @@ class TextEditor extends Model
     Grim.deprecate("This is now a view method. Call TextEditorElement::getWidth instead.")
     @displayBuffer.getWidth()
 
-  setFirstVisibleScreenRow: (@firstVisibleScreenRow) ->
+  # Experimental: Scroll the editor such that the given screen row is at the
+  # top of the visible area.
+  setFirstVisibleScreenRow: (screenRow, fromView) ->
+    unless fromView
+      maxScreenRow = @getLineCount() - 1
+      unless @config.get('editor.scrollPastEnd')
+        height = @displayBuffer.getHeight()
+        lineHeightInPixels = @displayBuffer.getLineHeightInPixels()
+        if height? and lineHeightInPixels?
+          maxScreenRow -= Math.floor(height / lineHeightInPixels)
+      screenRow = Math.min(screenRow, maxScreenRow)
+
+    unless screenRow is @firstVisibleScreenRow
+      @emitter.emit 'did-change-first-visible-screen-row', screenRow unless fromView
+      @firstVisibleScreenRow = screenRow
+
   getFirstVisibleScreenRow: -> @firstVisibleScreenRow
 
   setFirstVisibleScreenColumn: (@firstVisibleScreenColumn) ->
   getFirstVisibleScreenColumn: -> @firstVisibleScreenColumn
 
-
   getScrollTop: ->
     Grim.deprecate("This is now a view method. Call TextEditorElement::getScrollTop instead.")
 
@@ -3151,9 +3168,15 @@ class TextEditor extends Model
     @viewRegistry.getView(this).getMaxScrollTop()
 
   getVisibleRowRange: ->
-    Grim.deprecate("This is now a view method. Call TextEditorElement::getVisibleRowRange instead.")
-
-    @viewRegistry.getView(this).getVisibleRowRange()
+    height = @displayBuffer.getHeight()
+    lineHeightInPixels = @displayBuffer.getLineHeightInPixels()
+    if height? and lineHeightInPixels?
+      [
+        @firstVisibleScreenRow,
+        Math.min(@firstVisibleScreenRow + Math.floor(height / lineHeightInPixels), @getLineCount() - 1)
+      ]
+    else
+      null
 
   intersectsVisibleRowRange: (startRow, endRow) ->
     Grim.deprecate("This is now a view method. Call TextEditorElement::intersectsVisibleRowRange instead.")