[Newbies] Animation question

[LEnglish]

Because of garbage collection issues, smooth animation in Squeak isn’t really possible.

My little OpenGL spaceship firing a missile animation had this annoying pause every so-often, as the GC activated and froze the screen.

Was hoping that Craig Latta would release a minimal Spoon image that allowed me to load the OpenGL plugin code, because the GC in the minimal image took about 1/50th (or less) of the time that the complete image takes, but he got sidetracked with his Caffeine project.

Lawson

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
-Brian Kernighan



> On Oct 12, 2017, at 11:18, Bert Freudenberg <bert at freudenbergs.de> wrote:
> 
> No, you have to put that test in the step method, because it has to be checked every time the position changes.
> 
> Or you have to wait until the animation is done before doing the test - it does work in your first example with my "hack". It does not work in the second example because the forked code is executed after that test (plus forking is bad for this anyways).
> 
> - Bert -
> 
> On Thu, Oct 12, 2017 at 7:39 PM, obrienj <obrienj at protonmail.com <mailto:obrienj at protonmail.com>> wrote:
> The problem is that I want use something like (self position) >= (120 at 100) ifTrue: [self color: Color yellow] outside of the step method. Even though the morph moves, it's position remains unchanged and the boolean tests false. Hope this makes sense.
> 
> 
> 
>> -------- Original Message --------
>> Subject: Re: [Newbies] Animation question
>> Local Time: October 12, 2017 10:25 AM
>> UTC Time: October 12, 2017 5:25 PM
>> From: bert at freudenbergs.de <mailto:bert at freudenbergs.de>
>> To: obrienj <obrienj at protonmail.com <mailto:obrienj at protonmail.com>>, A friendly place to get answers to even the most basic questions about Squeak. <beginners at lists.squeakfoundation.org <mailto:beginners at lists.squeakfoundation.org>>
>> 
>> On Thu, Oct 12, 2017 at 6:24 PM, obrienj <obrienj at protonmail.com <mailto:obrienj at protonmail.com>> wrote:
>> I am having difficulty getting the following example to work using either delay or step:
>> 
>> aMorph := Morph new. 
>> aMorph position: (100 at 100).
>> aMorph openInWorld. 
>> 30 timesRepeat: [aMorph position: aMorph position +(1 at 0). Transcript show: 'test '; cr.]. 
>> (aMorph position) >= (120 at 100) ifTrue: [aMorph color: Color yellow].
>> Transcript show: 'position: ', aMorph position; cr.
>> 
>> For example:
>> 
>> aMorph := Morph new. 
>> aMorph position: (100 at 100). 
>> aMorph openInWorld. 
>> delay := Delay forMilliseconds: 20.
>> [30 timesRepeat: [aMorph position: aMorph position +(1 at 0). delay wait.].] fork. 
>> (aMorph position) >= (110 at 100) ifTrue: [aMorph color: Color yellow].
>> Transcript show: 'position: ', aMorph position; cr.
>> 
>> In the first example the morph moves, changes color, and the Transcript shows its final position. However, in the second example the morph moves but does not change color and the Transcript shows its starting position.
>> 
>> Morphic animation is based on stepping. That means, you don't move a Morph repeatedly in a loop, but Morphic tells your morph to update its position repeatedly.
>> 
>> You need to make your own Morph subclass and implement a "step" method. Whenever that method is called, it moves the morph by a little. For example, you could use an existing method called" translateBy:"
>> 
>> | aMorph |
>> aMorph := Morph new openInWorld. 
>> aMorph startStepping: #transformedBy: at: Time millisecondClockValue arguments: {MorphicTransform offset: -3 @ -3} stepTime: 200.
>> 
>> However, it's unlikely no existing method does your specific animation, so you indeed need to implement it, eg
>> 
>> step
>>     self position: self position + (1 at 0).
>>     (self position) >= (120 at 100) ifTrue: [self color: Color yellow].
>> 
>> So this is the Right Way. Without bad hacks you cannot do meaningful animation from a workspace. There is a hack however: If you insert "World doOneCycle" in the while loop of your first example, it will actually work, because it will redraw the world in each loop. However, this would prevent two objects animating independently, that's why the design calls for the "step" method approach.
>> 
>> - Bert -
>> 
> 
> 
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