Ensure combined scroll margins are smaller than editor height.

This prevents jerky scrolling when the window is very short.

spec/atom/editor-spec.coffee

@@ -44,29 +44,40 @@ describe "Editor", ->
       expect(editor.getPosition()).toEqual(row: 0, col: 0)
 
     describe "vertical movement", ->
+      describe "scroll margins", ->
+        beforeEach ->
+          editor.attachToDom()
+          editor.focus()
+          editor.scrollMargin = 3
 
-      fit "scrolls the buffer with the specified scroll margin when cursor approaches the end of the screen", ->
-        editor.attachToDom()
-        editor.focus()
-        editor.scrollMargin = 3
-        editor.height(editor.lineHeight * 10)
+        it "scrolls the buffer with the specified scroll margin when cursor approaches the end of the screen", ->
+          editor.height(editor.lineHeight * 10)
 
-        _.times 6, -> editor.moveDown()
-        expect(editor.scrollTop()).toBe(0)
+          _.times 6, -> editor.moveDown()
+          expect(editor.scrollTop()).toBe(0)
 
-        editor.moveDown()
-        expect(editor.scrollTop()).toBe(editor.lineHeight)
-        editor.moveDown()
-        expect(editor.scrollTop()).toBe(editor.lineHeight * 2)
+          editor.moveDown()
+          expect(editor.scrollTop()).toBe(editor.lineHeight)
+          editor.moveDown()
+          expect(editor.scrollTop()).toBe(editor.lineHeight * 2)
 
-        _.times 3, -> editor.moveUp()
-        expect(editor.scrollTop()).toBe(editor.lineHeight * 2)
+          _.times 3, -> editor.moveUp()
+          expect(editor.scrollTop()).toBe(editor.lineHeight * 2)
 
-        editor.moveUp()
-        expect(editor.scrollTop()).toBe(editor.lineHeight)
+          editor.moveUp()
+          expect(editor.scrollTop()).toBe(editor.lineHeight)
 
-        editor.moveUp()
-        expect(editor.scrollTop()).toBe(0)
+          editor.moveUp()
+          expect(editor.scrollTop()).toBe(0)
+
+        it "sacrifices margins when there isn't enough height", ->
+          editor.height(editor.lineHeight * 5)
+
+          _.times 3, -> editor.moveDown()
+          expect(editor.scrollTop()).toBe(editor.lineHeight)
+
+          editor.moveUp()
+          expect(editor.scrollTop()).toBe(0)
 
       describe "when up is pressed on the first line", ->
         it "moves the cursor to the beginning of the line, but retains the goal column", ->

spec/spec-helper.coffee

@@ -7,8 +7,8 @@ require 'window'
 
 afterEach ->
   (new Native).resetMainMenu()
-  # atom.globalKeymap.reset()
-  # $('#jasmine-content').empty()
+  atom.globalKeymap.reset()
+  $('#jasmine-content').empty()
 
 window.atom = new (require 'app')
 

src/atom/cursor.coffee

@@ -68,7 +68,11 @@ class Cursor extends Template
       position = @parentView.pixelPositionFromPoint(@point)
       @css(position)
 
-      margin = @parentView.scrollMargin * @height()
+      linesInView = @parentView.height() / @height()
+
+      maxScrollMargin = Math.floor((linesInView - 1) / 2)
+      scrollMargin = Math.min(@parentView.scrollMargin, maxScrollMargin)
+      margin = scrollMargin * @height()
       desiredTop = position.top - margin
       desiredBottom = position.top + @height() + margin