Use System variable in

the codes in picture could be run successfully,but i am confused.
i don’t know why i could’t use System variable directly in
i see the System variable could be used directly in java(processing).

help me.thank you very much!

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  • “System Variables” is merely a Processing’s “sugar” term.
  • Instead their actual nature is Java class instance fields.
  • That is, width, height, mouseX, sketchPath, etc. are simply fields from class PApplet:
  • When we assign a value to a variable outside a def we create a global variable:
    Globals \ Language (API)
  • If that variable happens to have the same name as a PApplet member, we end up overshadowing its corresponding __builtin__ property.
  • Once a PApplet member is overshadowed by a Python variable w/ the same name, we can still access the former via this or __builtin__ as a workaround:
width = 640 # global width overshadows __builtin__.width
print width, this.width # 640, 100

def setup():
    size(800, 600)
    print width, this.width, __builtin__.width # 640, 800, 800
  • Anyways, regardless the Processing flavor we’re coding on, it just makes sense to access width & height after size() has been invoked:
    size() \ Language (API)

This is key. Don’t declare this globally. They exist globally already, and they are defined by size() in setup(). Call size, then use them.


Your words are clear,i understand now.
You are so nice.
Thank you very very very much.

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Thank you very much.

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