relying on jQuery 1.9.0+ easing functions, added ease option

Author: kasparsj

README.md

@@ -38,7 +38,13 @@ $("#selector").parallax({
 });
 ```
 
-#### Supported properties:
+### Supported properties:
+
+Property value can be specified as number or percentage (string).
+To specify a **from** value as well **to**, use object syntax:
+```javascript
+{"to":1,"from":0}
+```
 
 translateX
 
@@ -52,14 +58,26 @@ rotate
 
 opacity
 
-#### Available options:
+### Available options:
 
 Options can be specified for all properties, or each individually
 
-**start** - number | selector
+#### start
+**Type:** number or selector
+**Default:** the elements top offset
+
+#### duration
+**Type:** number or percentage (string) or callback function
+**Default:** element top + height - start
 
-**duration** - number | percentage string | callback function
+#### trigger
+**Type:** number or percentage (string)
+**Default:**: "100%"
 
-**trigger** - number | percentage string
+#### ease
+**Type:** function or string
+**Default:** "linear"
 
-**axis** - "x" | "y"
+#### axis
+**Type:** string ("x" or "y")
+**Default:** "y"

bower.json

@@ -8,7 +8,7 @@
   "description": "jQuery plugin for easy parallax effect",
   "main": "jquery.parallax.js",
   "dependencies": {
-    "jquery": "*",
+    "jquery": ">=1.9.0",
     "requestAnimationFrame.js": "latest"
   },
   "keywords": [

jquery.parallax.js

@@ -221,18 +221,20 @@
         return value;
     }
 
-    function easeInOutQuad(t, b, c, d) {
-        return c*t/d + b;
-        //return -c/2 * (Math.cos(Math.PI*t/d) - 1) + b;
-    }
-
     function Scene($el, options, maxValue) {
         this.$el = $el;
         this.axis = options.axis;
         this.from = covertOption(options.from, maxValue);
         this.to = covertOption(options.to, maxValue);
         this.trigger = convertToPx(options.trigger, options.axis);
         this.start = convertToObj(options.start) || options.start;
+        if (typeof options.ease == "function") {
+            this.ease = options.ease;
+        }
+        else {
+            typeof options.ease == "undefined" || (this.ease = $.easing[options.ease]);
+            typeof this.ease == "function" || (this.ease = $.easing.linear);
+        }
         this.started = false;
 
         if (typeof options.duration != "undefined") {
@@ -248,6 +250,9 @@
             };
         }
     }
+    Scene.STATE_BEFORE = 'before';
+    Scene.STATE_DURING = 'during';
+    Scene.STATE_AFTER = 'after';
     Scene.prototype = {
         updateDuration: function() {
             this.startPx = Math.max(getOffset(this.start, this.axis) - this.trigger, 0);
@@ -260,26 +265,29 @@
             if (!this.started) {
                 this.updateDuration();
             }
-            var needsUpdate = (this.state == 'during');
+            var needsUpdate = (this.state == Scene.STATE_DURING);
             if (scrollTop < this.startPx) {
-                this.state = 'before';
+                this.state = Scene.STATE_BEFORE;
             }
             else if (scrollTop <= (this.startPx + this.durationPx)) {
-                this.state = 'during';
+                this.state = Scene.STATE_DURING;
                 this.started = true;
                 needsUpdate = true;
             }
             else {
-                this.state = 'after';
+                this.state = Scene.STATE_AFTER;
             }
             return needsUpdate;
         },
         value: function() {
-            if (this.state == 'before') {
+            if (this.state == Scene.STATE_BEFORE) {
                 return this.from;
             }
-            else if (this.state == 'during') {
-                return easeInOutQuad(scrollTop-this.startPx, this.from, (this.to - this.from), this.durationPx);
+            else if (this.state == Scene.STATE_DURING) {
+                var posPx = scrollTop - this.startPx,
+                    percent = posPx / this.durationPx,
+                    aniPos = this.ease.call(this, percent);
+                return (this.to - this.from) * aniPos + this.from;
             }
             else {
                 return this.to;