Support Constants (math) from Processing

[jeremydouglass]

Processing comes with a collection of defined constants. The ones featured in the reference:

• HALF_PI - https://processing.org/reference/HALF_PI.html
• PI https://processing.org/reference/PI.html
• QUARTER_PI https://processing.org/reference/QUARTER_PI.html
• TAU https://processing.org/reference/TAU.html
• TWO_PI https://processing.org/reference/TWO_PI.html

So, for example, the Processing.R example 3d-cube.R sketch begins:

PI <- 3.1415

And this line could be removed with the sketch still running correctly.

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Supporting more of these constants in Processing.R will make it much easier to translate sketches back and for between Processing(Java) and Processing.R -- especially for new learners.

[jeremydouglass]

Note that pi is a built-in constant in R, however I believe that these other values are not.

• https://stat.ethz.ch/R-manual/R-devel/library/base/html/Constants.html

It might be better to handle them all consistently in one way via PConstants:

• http://processing.github.io/processing-javadocs/core/processing/core/PConstants.html
• https://github.com/processing/processing/blob/master/core/src/processing/core/PConstants.java

[jeremydouglass]

...For Java libraries, the recommended use of PConstants is a simple import:

• https://github.com/processing/processing/wiki/Library-Basics

Perhaps renjin import() would work here?

• http://docs.renjin.org/en/latest/importing-java-classes-in-r-code.html

[gaocegege]

import(rprocessing.RLangPApplet)
print(RLangPApplet$P3D)

It works but I don't know why processing$P3D doesn't works.

Add getPI function into RLangPApplet and the code processing$getPI() works 🤔