[Qt-qml] Animating sprites - how do do it "right" ?

[Ville M. Vainio]

Just a thought - shouldn't collision detection reside on the c++ side? It should be pretty easy to tag a bunch of qml objects for collision detection check...

-- 
Sent from my Nokia N900

----- Original message -----
> The idea of declarative languages is to think in terms of rules that
> govern your scene. So, if one of your rules is: "the sprite must
> bounce everytime it touches an obstacle", you could express that by
> putting your collision detection code in
> a javascript function that gets callled from onXChanged and onYChanged.
> 
> This way, you now have the guarantee that no matter where your object
> goes, your rule will be applied, and the collision detection code will
> be executed.
> 
> Cheers,
> 
> Greg
> 
> 
> On Thu, Dec 30, 2010 at 2:39 PM, Tim Murphy <tnmurphy at gmail.com> wrote:
> > Hi,
> > 
> >  I have been playing with animations in QML and my current example
> > uses a timer and a bit of javascript to update the locations of my
> > "sprite" every 20ms or so. It seems to work.
> > 
> > I feel that I need to be involved in the position updates to the
> > sprite so that I can eventually detect collisions, implement the logic
> > for the sprites to react to the user's actions and to make them bounce
> > off, e.g., the sides of the window.
> > 
> > What I am doing seems wrong to me - not very declarative and using
> > lots of javascript to minutely control the position of the object. I
> > get the impression that I'm going to be in trouble when I try to rely
> > on my knowledge of where the item is because I'm guessing that it
> > might not have arrived where I sent it by the time the timer triggers
> > again.
> > 
> > I am wondering: is there a better way to do this?
> > 
> > My "spinner" object is just a bit of text that has a SmoothedAnimation
> > attached to it.  Here is the timer loop where I decide if the sprite
> > needs to bounce or not.  Strictly speaking I could calculate the
> > bounce point in advance and then I would not need this timer loop but
> > I am thinking about changing the animation more dynamically - e.g.
> > when I have multiple "spinners" they might bounce on collision.
> > 
> > Timer {
> > 
> > id: timer
> > interval: 20
> > repeat: true
> > running: true
> > onTriggered: {
> > 
> > spinner.rotation += 1
> > var newx = spinner.x + spinner.xinc
> > var newy = spinner.y + spinner.yinc
> > 
> > if (newx + spinner.width >= rect.width || newx <= 0) {
> > spinner.xinc = - spinner.xinc
> > }
> > if (newy + spinner.height >= rect.height|| newy <= 0) {
> > spinner.yinc = - spinner.yinc
> > }
> > 
> > spinner.x += spinner.xinc
> > spinner.y += spinner.yinc
> > }
> > }
> > 
> > --
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