Autoscroll the editor as a quadratic function of mouse cursor overshoot

This was a spike and still needs tests, but it’s going to be way better.

src/selection.coffee

@@ -190,7 +190,7 @@ class Selection extends Model
   # position.
   #
   # * `position` An instance of {Point}, with a given `row` and `column`.
-  selectToScreenPosition: (position) ->
+  selectToScreenPosition: (position, options) ->
     position = Point.fromObject(position)
 
     @modifySelection =>
@@ -200,12 +200,12 @@ class Selection extends Model
         else
           @marker.setScreenRange([@initialScreenRange.start, position], reversed: false)
       else
-        @cursor.setScreenPosition(position)
+        @cursor.setScreenPosition(position, options)
 
       if @linewise
-        @expandOverLine()
+        @expandOverLine(options)
       else if @wordwise
-        @expandOverWord()
+        @expandOverWord(options)
 
   # Public: Selects the text from the current cursor position to a given buffer
   # position.
@@ -311,28 +311,28 @@ class Selection extends Model
   # Public: Modifies the selection to encompass the current word.
   #
   # Returns a {Range}.
-  selectWord: ->
-    options = {}
+  selectWord: (options={}) ->
     options.wordRegex = /[\t ]*/ if @cursor.isSurroundedByWhitespace()
     if @cursor.isBetweenWordAndNonWord()
       options.includeNonWordCharacters = false
 
-    @setBufferRange(@cursor.getCurrentWordBufferRange(options))
+    @setBufferRange(@cursor.getCurrentWordBufferRange(options), options)
     @wordwise = true
     @initialScreenRange = @getScreenRange()
 
   # Public: Expands the newest selection to include the entire word on which
   # the cursors rests.
-  expandOverWord: ->
+  expandOverWord: (options) ->
     @setBufferRange(@getBufferRange().union(@cursor.getCurrentWordBufferRange()), autoscroll: false)
-    @cursor.autoscroll()
+    @cursor.autoscroll() if options?.autoscroll ? true
 
   # Public: Selects an entire line in the buffer.
   #
   # * `row` The line {Number} to select (default: the row of the cursor).
-  selectLine: (row=@cursor.getBufferPosition().row) ->
+  selectLine: (row, options) ->
+    row ?= @cursor.getBufferPosition().row
     range = @editor.bufferRangeForBufferRow(row, includeNewline: true)
-    @setBufferRange(@getBufferRange().union(range), autoscroll: true)
+    @setBufferRange(@getBufferRange().union(range), options)
     @linewise = true
     @wordwise = false
     @initialScreenRange = @getScreenRange()
@@ -341,10 +341,10 @@ class Selection extends Model
   # the cursor currently rests.
   #
   # It also includes the newline character.
-  expandOverLine: ->
+  expandOverLine: (options) ->
     range = @getBufferRange().union(@cursor.getCurrentLineBufferRange(includeNewline: true))
     @setBufferRange(range, autoscroll: false)
-    @cursor.autoscroll()
+    @cursor.autoscroll() if options?.autoscroll ? true
 
   ###
   Section: Modifying the selected text

src/text-editor-component.coffee

@@ -395,16 +395,16 @@ class TextEditorComponent
           if cursorAtScreenPosition and @editor.hasMultipleCursors()
             cursorAtScreenPosition.destroy()
           else
-            @editor.addCursorAtScreenPosition(screenPosition)
+            @editor.addCursorAtScreenPosition(screenPosition, autoscroll: false)
         else
-          @editor.setCursorScreenPosition(screenPosition)
+          @editor.setCursorScreenPosition(screenPosition, autoscroll: false)
       when 2
-        @editor.getLastSelection().selectWord()
+        @editor.getLastSelection().selectWord(autoscroll: false)
       when 3
-        @editor.getLastSelection().selectLine()
+        @editor.getLastSelection().selectLine(null, autoscroll: false)
 
     @handleDragUntilMouseUp (screenPosition) =>
-      @editor.selectToScreenPosition(screenPosition, true)
+      @editor.selectToScreenPosition(screenPosition, suppressSelectionMerge: true, autoscroll: false)
 
   onLineNumberGutterMouseDown: (event) =>
     return unless event.button is 0 # only handle the left mouse button
@@ -422,14 +422,14 @@ class TextEditorComponent
     clickedScreenRow = @screenPositionForMouseEvent(event).row
     clickedBufferRow = @editor.bufferRowForScreenRow(clickedScreenRow)
     initialScreenRange = @editor.screenRangeForBufferRange([[clickedBufferRow, 0], [clickedBufferRow + 1, 0]])
-    @editor.setSelectedScreenRange(initialScreenRange, preserveFolds: true)
+    @editor.setSelectedScreenRange(initialScreenRange, preserveFolds: true, autoscroll: false)
     @handleGutterDrag(initialScreenRange)
 
   onGutterMetaClick: (event) =>
     clickedScreenRow = @screenPositionForMouseEvent(event).row
     clickedBufferRow = @editor.bufferRowForScreenRow(clickedScreenRow)
     initialScreenRange = @editor.screenRangeForBufferRange([[clickedBufferRow, 0], [clickedBufferRow + 1, 0]])
-    @editor.addSelectionForScreenRange(initialScreenRange, preserveFolds: true)
+    @editor.addSelectionForScreenRange(initialScreenRange, preserveFolds: true, autoscroll: false)
     @handleGutterDrag(initialScreenRange)
 
   onGutterShiftClick: (event) =>
@@ -439,9 +439,9 @@ class TextEditorComponent
     clickedLineScreenRange = @editor.screenRangeForBufferRange([[clickedBufferRow, 0], [clickedBufferRow + 1, 0]])
 
     if clickedScreenRow < tailScreenPosition.row
-      @editor.selectToScreenPosition(clickedLineScreenRange.start, true)
+      @editor.selectToScreenPosition(clickedLineScreenRange.start, suppressSelectionMerge: true, autoscroll: false)
     else
-      @editor.selectToScreenPosition(clickedLineScreenRange.end, true)
+      @editor.selectToScreenPosition(clickedLineScreenRange.end, suppressSelectionMerge: true, autoscroll: false)
 
     @handleGutterDrag(new Range(tailScreenPosition, tailScreenPosition))
 
@@ -456,7 +456,6 @@ class TextEditorComponent
         endPosition = [dragRow + 1, 0]
         screenRange = new Range(endPosition, endPosition).union(initialRange)
         @editor.getLastSelection().setScreenRange(screenRange, reversed: false, autoscroll: false, preserveFolds: true)
-      @editor.getLastCursor().autoscroll()
 
   onStylesheetsChanged: (styleElement) =>
     return unless @performedInitialMeasurement
@@ -512,7 +511,9 @@ class TextEditorComponent
     animationLoop = =>
       @requestAnimationFrame =>
         if dragging and @mounted
-          screenPosition = @screenPositionForMouseEvent(lastMousePosition)
+          linesClientRect = @linesComponent.getDomNode().getBoundingClientRect()
+          autoscroll(lastMousePosition, linesClientRect)
+          screenPosition = @screenPositionForMouseEvent(lastMousePosition, linesClientRect)
           dragHandler(screenPosition)
           animationLoop()
         else if not @mounted
@@ -543,6 +544,32 @@ class TextEditorComponent
       window.removeEventListener('mouseup', onMouseUp)
       willInsertTextSubscription.dispose()
 
+    autoscroll = (mouseClientPosition) =>
+      editorClientRect = @domNode.getBoundingClientRect()
+
+      if mouseClientPosition.clientY < editorClientRect.top
+        mouseYDelta = editorClientRect.top - mouseClientPosition.clientY
+        yDirection = -1
+      else if mouseClientPosition.clientY > editorClientRect.bottom
+        mouseYDelta = mouseClientPosition.clientY - editorClientRect.bottom
+        yDirection = 1
+
+      if mouseClientPosition.clientX < editorClientRect.left
+        mouseXDelta = editorClientRect.left - mouseClientPosition.clientX
+        xDirection = -1
+      else if mouseClientPosition.clientX > editorClientRect.right
+        mouseXDelta = mouseClientPosition.clientX - editorClientRect.right
+        xDirection = 1
+
+      if mouseYDelta?
+        @presenter.setScrollTop(@presenter.getScrollTop() + yDirection * scaleScrollDelta(mouseYDelta))
+
+      if mouseXDelta?
+        @presenter.setScrollLeft(@presenter.getScrollLeft() + xDirection * scaleScrollDelta(mouseXDelta))
+
+    scaleScrollDelta = (scrollDelta) ->
+      Math.pow(scrollDelta / 2, 3) / 280
+
     pasteSelectionClipboard = (event) =>
       if event?.which is 2 and process.platform is 'linux'
         if selection = require('./safe-clipboard').readText('selection')
@@ -748,17 +775,20 @@ class TextEditorComponent
     if scrollSensitivity = parseInt(scrollSensitivity)
       @scrollSensitivity = Math.abs(scrollSensitivity) / 100
 
-  screenPositionForMouseEvent: (event) ->
-    pixelPosition = @pixelPositionForMouseEvent(event)
+  screenPositionForMouseEvent: (event, linesClientRect) ->
+    pixelPosition = @pixelPositionForMouseEvent(event, linesClientRect)
     @editor.screenPositionForPixelPosition(pixelPosition)
 
-  pixelPositionForMouseEvent: (event) ->
+  pixelPositionForMouseEvent: (event, linesClientRect) ->
     {clientX, clientY} = event
 
-    linesClientRect = @linesComponent.getDomNode().getBoundingClientRect()
+    linesClientRect ?= @linesComponent.getDomNode().getBoundingClientRect()
     top = clientY - linesClientRect.top + @presenter.scrollTop
     left = clientX - linesClientRect.left + @presenter.scrollLeft
-    {top, left}
+    bottom = linesClientRect.top + @presenter.scrollTop + linesClientRect.height - clientY
+    right = linesClientRect.left + @presenter.scrollLeft + linesClientRect.width - clientX
+
+    {top, left, bottom, right}
 
   getModel: ->
     @editor

src/text-editor.coffee

@@ -1943,10 +1943,10 @@ class TextEditor extends Model
   # This method may merge selections that end up intesecting.
   #
   # * `position` An instance of {Point}, with a given `row` and `column`.
-  selectToScreenPosition: (position, suppressMerge) ->
+  selectToScreenPosition: (position, options) ->
     lastSelection = @getLastSelection()
-    lastSelection.selectToScreenPosition(position)
-    unless suppressMerge
+    lastSelection.selectToScreenPosition(position, options)
+    unless options?.suppressSelectionMerge
       @mergeIntersectingSelections(reversed: lastSelection.isReversed())
 
   # Essential: Move the cursor of each selection one character upward while