Honor the center: true option in scrollTo* methods

Fixes #2648

spec/display-buffer-spec.coffee

@@ -1044,17 +1044,26 @@ describe "DisplayBuffer", ->
       expect(displayBuffer.setScrollLeft(maxScrollLeft + 50)).toBe maxScrollLeft
       expect(displayBuffer.getScrollLeft()).toBe maxScrollLeft
 
-  describe "::scrollToScreenPosition(position)", ->
-    it "sets the scroll top and scroll left so the given screen position is in view", ->
+  describe "::scrollToScreenPosition(position, [options])", ->
+    beforeEach ->
       displayBuffer.manageScrollPosition = true
       displayBuffer.setLineHeightInPixels(10)
       displayBuffer.setDefaultCharWidth(10)
       displayBuffer.setHorizontalScrollbarHeight(0)
-
       displayBuffer.setHeight(50)
       displayBuffer.setWidth(50)
-      maxScrollTop = displayBuffer.getScrollHeight() - displayBuffer.getHeight()
 
+    it "sets the scroll top and scroll left so the given screen position is in view", ->
       displayBuffer.scrollToScreenPosition([8, 20])
       expect(displayBuffer.getScrollBottom()).toBe (9 + displayBuffer.getVerticalScrollMargin()) * 10
       expect(displayBuffer.getScrollRight()).toBe (20 + displayBuffer.getHorizontalScrollMargin()) * 10
+
+    describe "when the 'center' option is true", ->
+      it "vertically scrolls to center the given position vertically", ->
+        displayBuffer.scrollToScreenPosition([8, 20], center: true)
+        expect(displayBuffer.getScrollTop()).toBe (8 * 10) + 5 - (50 / 2)
+        expect(displayBuffer.getScrollRight()).toBe (20 + displayBuffer.getHorizontalScrollMargin()) * 10
+
+      it "does not scroll vertically if the position is already in view", ->
+        displayBuffer.scrollToScreenPosition([4, 20], center: true)
+        expect(displayBuffer.getScrollTop()).toBe 0

src/display-buffer.coffee

@@ -254,15 +254,23 @@ class DisplayBuffer extends Model
     {start, end} = selection.getScreenRange()
     @intersectsVisibleRowRange(start.row, end.row + 1)
 
-  scrollToScreenRange: (screenRange) ->
+  scrollToScreenRange: (screenRange, options) ->
     verticalScrollMarginInPixels = @getVerticalScrollMargin() * @getLineHeightInPixels()
     horizontalScrollMarginInPixels = @getHorizontalScrollMargin() * @getDefaultCharWidth()
 
     {top, left, height, width} = @pixelRectForScreenRange(screenRange)
     bottom = top + height
     right = left + width
-    desiredScrollTop = top - verticalScrollMarginInPixels
-    desiredScrollBottom = bottom + verticalScrollMarginInPixels
+
+    if options?.center
+      desiredScrollCenter = top + height / 2
+      unless @getScrollTop() < desiredScrollCenter < @getScrollBottom()
+        desiredScrollTop =  desiredScrollCenter - @getHeight() / 2
+        desiredScrollBottom =  desiredScrollCenter + @getHeight() / 2
+    else
+      desiredScrollTop = top - verticalScrollMarginInPixels
+      desiredScrollBottom = bottom + verticalScrollMarginInPixels
+
     desiredScrollLeft = left - horizontalScrollMarginInPixels
     desiredScrollRight = right + horizontalScrollMarginInPixels
 
@@ -276,11 +284,11 @@ class DisplayBuffer extends Model
     else if desiredScrollRight > @getScrollRight()
       @setScrollRight(desiredScrollRight)
 
-  scrollToScreenPosition: (screenPosition) ->
-    @scrollToScreenRange(new Range(screenPosition, screenPosition))
+  scrollToScreenPosition: (screenPosition, options) ->
+    @scrollToScreenRange(new Range(screenPosition, screenPosition), options)
 
-  scrollToBufferPosition: (bufferPosition) ->
-    @scrollToScreenPosition(@screenPositionForBufferPosition(bufferPosition))
+  scrollToBufferPosition: (bufferPosition, options) ->
+    @scrollToScreenPosition(@screenPositionForBufferPosition(bufferPosition), options)
 
   pixelRectForScreenRange: (screenRange) ->
     if screenRange.end.row > screenRange.start.row

src/editor.coffee

@@ -2023,11 +2023,11 @@ class Editor extends Model
 
   pixelRectForScreenRange: (screenRange) -> @displayBuffer.pixelRectForScreenRange(screenRange)
 
-  scrollToScreenRange: (screenRange) -> @displayBuffer.scrollToScreenRange(screenRange)
+  scrollToScreenRange: (screenRange, options) -> @displayBuffer.scrollToScreenRange(screenRange, options)
 
-  scrollToScreenPosition: (screenPosition) -> @displayBuffer.scrollToScreenPosition(screenPosition)
+  scrollToScreenPosition: (screenPosition, options) -> @displayBuffer.scrollToScreenPosition(screenPosition, options)
 
-  scrollToBufferPosition: (bufferPosition) -> @displayBuffer.scrollToBufferPosition(bufferPosition)
+  scrollToBufferPosition: (bufferPosition, options) -> @displayBuffer.scrollToBufferPosition(bufferPosition, options)
 
   horizontallyScrollable: -> @displayBuffer.horizontallyScrollable()
 

src/react-editor-view.coffee

@@ -69,11 +69,11 @@ class ReactEditorView extends View
   scrollToBottom: ->
     @editor.setScrollBottom(Infinity)
 
-  scrollToScreenPosition: (screenPosition) ->
-    @editor.scrollToScreenPosition(screenPosition)
+  scrollToScreenPosition: (screenPosition, options) ->
+    @editor.scrollToScreenPosition(screenPosition, options)
 
-  scrollToBufferPosition: (bufferPosition) ->
-    @editor.scrollToBufferPosition(bufferPosition)
+  scrollToBufferPosition: (bufferPosition, options) ->
+    @editor.scrollToBufferPosition(bufferPosition, options)
 
   scrollToCursorPosition: ->
     @editor.scrollToCursorPosition()