Add scroll animation.

lib/main.coffee

@@ -78,6 +78,10 @@ class Main
       minimum: 0
       maximum: 1
       description: "The opacity used to render the line's text in the minimap."
+    scrollAnimation:
+      type: 'boolean'
+      default: false
+      description: "If this option is enabled then when you click the minimap it will scroll to the destination with animation"
 
   # Internal: The activation state of the minimap package.
   active: false

lib/minimap-element.coffee

@@ -5,6 +5,25 @@ CanvasDrawer = require './mixins/canvas-drawer'
 
 MinimapQuickSettingsView = null
 
+animate = ({from, to, duration, step}) ->
+  start = new Date()
+
+  swing = (progress) ->
+    return 0.5 - Math.cos( progress * Math.PI ) / 2
+
+  update = ->
+    passed = new Date() - start
+    if duration == 0
+      progress = 1
+    else
+      progress = passed / duration
+    progress = 1 if progress > 1
+    delta = swing(progress)
+    step(from + (to-from)*delta)
+    requestAnimationFrame(update) if progress < 1
+
+  update()
+
 # Public:
 class MinimapElement extends HTMLElement
   DOMStylesReader.includeInto(this)
@@ -353,7 +372,16 @@ class MinimapElement extends HTMLElement
 
     scrollTop = row * @minimap.textEditor.getLineHeightInPixels() - @minimap.textEditor.getHeight() / 2
 
-    @minimap.textEditor.setScrollTop(scrollTop)
+    from = @minimap.textEditor.getScrollTop()
+    to = scrollTop
+    step = (now) =>
+      @minimap.textEditor.setScrollTop(now)
+    if atom.config.get('minimap.scrollAnimation')
+      duration = 300
+    else
+      duration = 0
+    animate(from: from, to: to, duration: duration, step: step)
+
   relayMousewheelEvent: (e) =>
     editorElement = atom.views.getView(@minimap.textEditor)
 

spec/minimap-element-spec.coffee

@@ -67,7 +67,7 @@ describe 'MinimapElement', ->
   #    ##     ##    ##       ##    ##     ##  ######  ##     ##
 
   describe 'when attached to the text editor element', ->
-    [nextAnimationFrame, canvas, visibleArea] = []
+    [noAnimationFrame, nextAnimationFrame, canvas, visibleArea] = []
 
     beforeEach ->
       jasmineContent = document.body.querySelector('#jasmine-content')
@@ -263,15 +263,34 @@ describe 'MinimapElement', ->
         it 'relays the events to the editor view', ->
           expect(editor.setScrollTop).toHaveBeenCalled()
 
-      describe 'pressing the mouse on the minimap canvas', ->
+      describe 'pressing the mouse on the minimap canvas (without scroll animation)', ->
         beforeEach ->
+          atom.config.set 'minimap.scrollAnimation', false
           canvas = minimapElement.canvas
           mousedown(canvas)
           nextAnimationFrame()
 
         it 'scrolls the editor to the line below the mouse', ->
           expect(editor.getScrollTop()).toEqual(360)
 
+      describe 'pressing the mouse on the minimap canvas (with scroll animation)', ->
+        beforeEach ->
+          atom.config.set 'minimap.scrollAnimation', true
+          canvas = minimapElement.canvas
+          mousedown(canvas)
+          nextAnimationFrame()
+
+        it 'scrolls the editor gradually to the line below the mouse', ->
+          expect(editor.getScrollTop()).toEqual(0)
+
+          #wait until all animations run out
+          waitsFor ->
+            nextAnimationFrame()
+            return nextAnimationFrame == noAnimationFrame
+
+          runs ->
+            expect(editor.getScrollTop()).toEqual(360)
+
       describe 'dragging the visible area', ->
         [visibleArea, originalTop] = []