support page down/up navigation

Editor.js

@@ -3,6 +3,8 @@ var keys = {
   RIGHT: 39,
   DOWN: 40,  
   LEFT: 37,
+  PAGEUP: 33,
+  PAGEDOWN: 34,
   POS1: 36,
   END: 35,
   DELETE: 46,
@@ -67,6 +69,14 @@ function KeyBinding(element, host)
         }
         return lib.stopEvent(e);
         
+      case keys.PAGEDOWN:
+        host.scrollPageDown();
+        return lib.stopEvent(e);
+        
+      case keys.PAGEUP:
+        host.scrollPageUp();
+        return lib.stopEvent(e);        
+        
       case keys.POS1:
         if (e.shiftKey) {
           host.selectLineStart();
@@ -350,6 +360,26 @@ function Editor(doc, renderer)
     this.removeLeft();
   },
   
+  getPageDownRow : function() {
+    return this.renderer.getLastVisibleRow() - 1;
+  },
+  
+  getPageUpRow : function()
+  {
+    var firstRow = this.renderer.getFirstVisibleRow(); 
+    var lastRow = this.renderer.getLastVisibleRow();
+    
+    return firstRow - (lastRow-firstRow) + 1;       
+  },
+  
+  scrollPageDown : function() {
+    this.renderer.scrollToRow(this.getPageDownRow());
+  },
+
+  scrollPageUp : function() {
+    this.renderer.scrollToRow(this.getPageUpRow());
+  },
+  
   navigateUp : function() 
   {
     this.clearSelection();

VirtualRenderer.js

@@ -46,6 +46,14 @@ VirtualRenderer.prototype.getContainerElement = function() {
   return this.container;
 };
 
+VirtualRenderer.prototype.getFirstVisibleRow = function() {
+  return this.layerConfig.firstRow || 0;
+};
+
+VirtualRenderer.prototype.getLastVisibleRow = function() {
+  return this.layerConfig.lastRow || 0;
+};
+
 VirtualRenderer.prototype.updateLines = function(firstRow, lastRow)
 {
   var layerConfig = this.layerConfig;
@@ -157,6 +165,10 @@ VirtualRenderer.prototype.getScrollTop = function() {
   return this.scrollTop;
 };
 
+VirtualRenderer.prototype.scrollToRow = function(row) {
+  this.scrollToY(row*this.lineHeight);
+}
+
 VirtualRenderer.prototype.scrollToY = function(scrollTop)
 {
   var maxHeight = this.lines.length * this.lineHeight - this.scroller.clientHeight;