Scrolling to bottom renders correct lines

When we scroll more than a single screen's worth of lines, the new first visible screen row ends up exceeding the previous last rendered screen row, so we need to use the maximum of the two when deciding which new rows to render.

spec/app/editor-spec.coffee

@@ -401,7 +401,7 @@ describe "Editor", ->
         expectedMarginBottom = (buffer.numLines() - 6) * editor.lineHeight
         expect(editor.lines.find('.line:last').css('margin-bottom')).toBe "#{expectedMarginBottom}px"
 
-      fit "when the lines are scrolled down, removes lines that become invisible and build lines that are become visisble", ->
+      it "when the lines are scrolled down, removes lines that become invisible and builds lines that become visisble", ->
         editor.scroller.scrollTop(editor.lineHeight * 2.5)
         editor.scroller.trigger 'scroll'
 
@@ -416,6 +416,14 @@ describe "Editor", ->
         expect(editor.lines.find('.line:first').text()).toBe buffer.lineForRow(3)
         expect(editor.lines.find('.line:last').text()).toBe buffer.lineForRow(8)
 
+      fit "when the scroller is scrolled to the end, removes lines that become invisible and builds lines that become visible", ->
+        editor.scroller.scrollBottom(editor.scroller[0].scrollHeight)
+        editor.scroller.trigger 'scroll'
+
+        expect(editor.lines.find('.line').length).toBe 6
+        expect(editor.lines.find('.line:first').text()).toBe buffer.lineForRow(7)
+        expect(editor.lines.find('.line:last').text()).toBe buffer.lineForRow(12)
+
       it "adjusts margins to account for non-rendered lines", ->
         editor.scroller.scrollTop(editor.lineHeight * 2.5)
         editor.scroller.trigger 'scroll'

src/app/editor.coffee

@@ -243,27 +243,30 @@ class Editor extends View
     @firstRenderedScreenRow = 0
     @lastRenderedScreenRow = @getLastVisibleScreenRow()
 
-    lineElements = @buildLineElements(@firstRenderedScreenRow, @lastRenderedScreenRow)
-    lineElements.last().css('margin-bottom', (@getLastScreenRow() - @lastRenderedScreenRow) * @lineHeight)
-    @insertLineElements(0, lineElements)
+    @insertLineElements(0, @buildLineElements(@firstRenderedScreenRow, @lastRenderedScreenRow))
+    @lines.css('padding-bottom', (@getLastScreenRow() - @lastRenderedScreenRow) * @lineHeight)
 
   updateLines: ->
     firstVisibleScreenRow = @getFirstVisibleScreenRow()
     lastVisibleScreenRow = @getLastVisibleScreenRow()
 
+    console.log "updateLines", firstVisibleScreenRow, lastVisibleScreenRow
+    # console.log "cursor screen position", @getCursorScreenPosition().inspect()
+
     if firstVisibleScreenRow > @firstRenderedScreenRow
-      @lines.find('.line:first').css('margin-top', 'inherit')
+      console.log "removing from", @firstRenderedScreenRow, "to", firstVisibleScreenRow - 1
       @removeLineElements(@firstRenderedScreenRow, firstVisibleScreenRow - 1)
-      @lines.find('.line:first').css('margin-top', firstVisibleScreenRow * @lineHeight)
+      @lines.css('padding-top', firstVisibleScreenRow * @lineHeight)
+      console.log @lines
 
     if lastVisibleScreenRow > @lastRenderedScreenRow
-      @lines.find('.line:last').css('margin-bottom', 'inherit')
-      lineElements = @buildLineElements(@lastRenderedScreenRow + 1, lastVisibleScreenRow)
-      lineElements.last().css('margin-bottom', (@getLastScreenRow() - lastVisibleScreenRow) * @lineHeight)
-      @insertLineElements(@lastRenderedScreenRow + 1, lineElements)
-      @lastRenderedScreenRow = lastVisibleScreenRow
+      startRow = Math.max(@lastRenderedScreenRow + 1, firstVisibleScreenRow)
+      lineElements = @buildLineElements(startRow, lastVisibleScreenRow)
+      @insertLineElements(startRow, lineElements)
+      @lines.css('padding-bottom', (@getLastScreenRow() - lastVisibleScreenRow) * @lineHeight)
 
     @firstRenderedScreenRow = firstVisibleScreenRow
+    @lastRenderedScreenRow = lastVisibleScreenRow
 
   getFirstVisibleScreenRow: ->
     Math.floor(@scroller.scrollTop() / @lineHeight)