On Friday, October 24, 2014 11:14:56 AM UTC-4, Fluid Dynamics wrote:
>
> On Friday, October 24, 2014 10:42:37 AM UTC-4, Kasper Jordaens wrote:
>>
>> Hey,
>>
>> I've been experimenting with newtonian, I love it, but I have a simple
>> question, because I'm stuck
>>
>> after adding some emitters
>>
>> [#newtonian.corporum.ParticleEmitter{:position
>> #newtonian.utils.Vector2D{:x 23.0, :y 280.0}, :velocity
>> #newtonian.utils.Vector2D{:x 0.0, :y 10.0}, :size 8, :life -1, :spread
>> 0.09817477042468103, :emission-rate 4}
>> #newtonian.corporum.ParticleEmitter{:position #newtonian.utils.Vector2D{:x
>> 200.0, :y 280.0}, :velocity #newtonian.utils.Vector2D{:x 0.0, :y 10.0},
>> :size 8, :life -1, :spread 0.09817477042468103, :emission-rate 4}]
>>
>>
>> I want to dynamically change them but this seems to be inaccessible as an
>> atom?
>>
>> I can get to individual objects like
>>
>> (get (nth @newt/emitters 0) :position) ==> #newtonian.utils.Vector2D{:x
>> 23.0, :y 280.0}
>>
>>
>> but how can I swap the atom at Vector2D?
>>
>>
>> (swap! (get (nth @newt/emitters 0) :position) :x 200) ==> java.lang.
>> ClassCastException: newtonian.utils.Vector2D cannot be cast to clojure.
>> lang.Atom core.clj:2233 clojure.core/swap!
>>
>>
> What you want here is update-in. Try
>
> (swap! newt update-in [:emitters 0 :position] assoc :x 200)
>
> assuming that @newt is a map with an :emitters key. I'm not familiar with
> the library and I'm not even sure what kind of object could be in the atom
> newt that @newt/emitters makes sense, but when you want to "change" a thing
> buried deep in a nested associative data structure the usual tool for that
> is update-in.
>
I looked briefly at the newtonian docs and it looks like newt/emitters is
the atom, hmm, global vars? Anyway you just want
(swap! newt/emitters update-in [0 :position] assoc :x 200)
then, to replace the value of x in the first emitter. You could also use
(swap! newt/emitters update-in [0 :position :x] + 100)
and the like to "move" that emitter's x around relative to where it was,
here 100 units further right one presumes.
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