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BlitMask & ThrowProps | Change target displayObject content dynamically!

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Hi everyone!


First, congrats for the awesome new website.. very refreshing!!

Second sorry for my english but that's not my native language..


Following your example using ThrowProps with BlitMask, I need to edit the content of the target DisplayObject on the fly but I can't manage it.


My target is a MovieClip with datas from a contact form.


At startup, I fill my target with datas saved previously (with a SharedObject- this is an AIR app).

Then I create the BlitMask and everything works fine.


But when I try adding more contacts, they don't add anymore in the target object.

I guess I know why : because BlitMask is a bitmap version of my target, right?


Can you help?

(I hope my description is clear enough)


Thank you.



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Oh no, Jack!! I promise I've tried the update() method !!

But the wrong way apparently!


OK I try again.

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  • 2 weeks later...

Could someone point me to where this ThrowProps with BlitMask example (mentioned in the initial post) is please?



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Thanks Carl. I did already have this reference but when I've tried to add it to a blitmask I don't get anything appearing in screen.

The post seemed to suggest there was a working example of ThrowProps and Blitmask together but I'm assuming that was incorrect?

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I'm not so sure I follow you. The interactive demo on the ThrowProps page has code that you can literally paste into a blank fla and it will work.

That demo uses BlitMask and ThrowProps together.


You just need to make sure the fla has access to the bonus plugins.


Here is the code to save you a step:


import com.greensock.*; 
import com.greensock.easing.*;
import com.greensock.plugins.*;
import flash.geom.Rectangle;
import flash.utils.getTimer;
import flash.events.MouseEvent;
import flash.text.*;
import flash.display.*;

var bounds:Rectangle = new Rectangle(30, 30, 250, 230);
var mc:Sprite = new Sprite();
setupTextField(mc, bounds);
var blitMask:BlitMask = new BlitMask(mc, bounds.x, bounds.y, bounds.width, bounds.height, false);

var t1:uint, t2:uint, y1:Number, y2:Number, yOverlap:Number, yOffset:Number;

blitMask.addEventListener(MouseEvent.MOUSE_DOWN, mouseDownHandler);

function mouseDownHandler(event:MouseEvent):void {
y1 = y2 = mc.y;
yOffset = this.mouseY - mc.y;
yOverlap = Math.max(0, mc.height - bounds.height);
t1 = t2 = getTimer();
mc.stage.addEventListener(MouseEvent.MOUSE_MOVE, mouseMoveHandler);
mc.stage.addEventListener(MouseEvent.MOUSE_UP, mouseUpHandler);

function mouseMoveHandler(event:MouseEvent):void {
var y:Number = this.mouseY - yOffset;
//if mc's position exceeds the bounds, make it drag only half as far with each mouse movement (like iPhone/iPad behavior)
if (y > bounds.top) {
mc.y = (y + bounds.top) * 0.5;
} else if (y < bounds.top - yOverlap) {
mc.y = (y + bounds.top - yOverlap) * 0.5;
} else {
mc.y = y;
var t:uint = getTimer();
//if the frame rate is too high, we won't be able to track the velocity as well, so only update the values 20 times per second
if (t - t2 > 50) {
y2 = y1;
t2 = t1;
y1 = mc.y;
t1 = t;

function mouseUpHandler(event:MouseEvent):void {
mc.stage.removeEventListener(MouseEvent.MOUSE_UP, mouseUpHandler);
mc.stage.removeEventListener(MouseEvent.MOUSE_MOVE, mouseMoveHandler);
var time:Number = (getTimer() - t2) / 1000;
var yVelocity:Number = (mc.y - y2) / time;
ThrowPropsPlugin.to(mc, {throwProps:{
y:{velocity:yVelocity, max:bounds.top, min:bounds.top - yOverlap, resistance:300}
}, onUpdate:blitMask.update, ease:Strong.easeOut
}, 10, 0.3, 1);

function setupTextField(container:Sprite, bounds:Rectangle, padding:Number=20):void {
var tf:TextField = new TextField();
tf.width = bounds.width - padding;
tf.x = tf.y = padding / 2;
tf.defaultTextFormat = new TextFormat("_sans", 12);
tf.text = "Click and drag this content and then let go as you're dragging to throw it. Notice how it smoothly glides into place, respecting the initial velocity and the maximum/minimum coordinates.\n\nThrowPropsPlugin allows you to simply define an initial velocity for a property (or multiple properties) as well as optional maximum and/or minimum end values and then it will calculate the appropriate landing position and plot a smooth course based on the easing equation you define (Quad.easeOut by default, as set in TweenLite). This is perfect for flick-scrolling or animating things as though they are being thrown.\n\nFor example, let's say a user clicks and drags a ball and you track its velocity using an ENTER_FRAME handler and then when the user releases the mouse button, you'd determine the velocity but you can't do a normal tween because you don't know exactly where it should land or how long the tween should last (faster initial velocity would mean a longer duration). You need the tween to pick up exactly where the user left off so that it appears to smoothly continue moving at the same velocity they were dragging and then decelerate based on whatever ease you define in your tween.\n\nAs demonstrated here, maybe the final resting value needs to lie within a particular range so that the content doesn't land outside a particular area. But you don't want it to suddenly jerk to a stop when it hits the edge; instead, you want it to ease gently into place even if that means going past the landing spot briefly and easing back (if the initial velocity is fast enough to require that). The whole point is to make it look smooth.\n\nThrowPropsPlugin isn't just for tweening x and y coordinates. It works with any numeric property, so you could use it for spinning the rotation of an object as well. Or the scaleX/scaleY properties. Maybe the user drags to spin a wheel and lets go and you want it to continue increasing the rotation at that velocity, decelerating smoothly until it stops.\n\nOne of the trickiest parts of creating a throwProps tween that looks fluid and natural, particularly if you're applying maximum and/or minimum values, is determining its duration. Typically it's best to have a relatively consistent level of resistance so that if the initial velocity is very fast, it takes longer for the object to come to rest compared to when the initial velocity is slower. You also may want to impose some restrictions on how long a tween can last (if the user drags incredibly fast, you might not want the tween to last 200 seconds). The duration will also affect how far past a max/min boundary the property can potentially go, so you might want to only allow a certain amount of overshoot tolerance. That's why ThrowPropsPlugin has a few static helper methods that make managing all these variables much easier. The one you'll probably use most often is the to() method which is very similar to TweenLite.to() except that it doesn't have a duration parameter and it adds several other optional parameters.\n\nA unique convenience of ThrowPropsPlugin compared to most other solutions out there which use ENTER_FRAME loops is that everything is reverseable and you can jump to any spot in the tween immediately. So if you create several throwProps tweens, for example, and dump them into a TimelineLite, you could simply call reverse() on the timeline to watch the objects retrace their steps right back to the beginning.\n\nThe overshootTolerance parameter sets a maximum number of seconds that can be added to the tween's duration (if necessary) to accommodate temporarily overshooting the end value before smoothly returning to it at the end of the tween. This can happen in situations where the initial velocity would normally cause it to exceed the max or min values. An example of this would be in the iOS (iPhone or iPad) when you flick-scroll so quickly that the content would shoot past the end of the scroll area. Instead of jerking to a sudden stop when it reaches the edge, the content briefly glides past the max/min position and gently eases back into place. The larger the overshootTolerance the more leeway the tween has to temporarily shoot past the max/min if necessary.";
tf.multiline = tf.wordWrap = true;
tf.selectable = false;
tf.autoSize = TextFieldAutoSize.LEFT;

container.graphics.beginFill(0xFFFFFF, 1);
container.graphics.drawRect(0, 0, tf.width + padding, tf.textHeight + padding);
container.x = bounds.x;
container.y = bounds.y;


In addition I've attached a simple demo of ThrowProps and BlitMask that works horizontally



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Thanks Carl. That is a great reply. Very thorough.
The confusion is that I am using the example at the bottom of the page (panel scrolling) which I now realise doesn't use ThrowProps!
This still doesn't seem to like having a BlitMask applied to it though.
The example uses the 400px stage to do it's masking but what I'm after is creating a 400px wide scroll area sat on a 1024px stage.
Perhaps I'm missing something. I've downloaded the files, run them to test everything is working.
Then added a blitmask like this:

private function _xmlCompleteHandler(event:LoaderEvent):void {
var panels:XMLList = event.target.content.panel;
_panelCount = panels.length();
var queue:LoaderMax = new LoaderMax();
for (var i:int = 0; i < _panelCount; i++) {
queue.append( new ImageLoader("assets/" + panels[i].@file, {x:i * _panelBounds.width, width:_panelBounds.width, height:_panelBounds.height, container:_container}) );
var _blitMaskB:BlitMask = new BlitMask(_container, 0, 0, 400, 100, true, true, 0xFF0000, true);

But I just get a black screen when testing?

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Ok so after a little fiddling it seems that the issue was that the blitmask was being applied before the bitmaps had been loaded.

var queue:LoaderMax = new LoaderMax({onComplete:loadCompleteHandler});
private function loadCompleteHandler(event:LoaderEvent):void {
if (!_blitMask) {
_blitMask = new BlitMask(_container, 0, 0, 400, 100, true, true, 0xFF0000, true);
_blitMask.addEventListener(MouseEvent.MOUSE_DOWN, _mouseDownHandler, false, 0, true);

Seems to be visible now. Thanks again for the great reply.

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