[MacPorts] #62011: opencv3/opencv4: eliminate portfile duplication via subports; simplify via portgroups; streamline python binding generation (was: opencv3/opencv4: eliminate portfile duplication via subports; simplify via portgroups; )

[MacPorts]

#62011: opencv3/opencv4: eliminate portfile duplication via subports; simplify via
portgroups; streamline python binding generation
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  Reporter:  mascguy          |      Owner:  mascguy
      Type:  enhancement      |     Status:  assigned
  Priority:  Normal           |  Milestone:
 Component:  ports            |    Version:
Resolution:                   |   Keywords:
      Port:  opencv3 opencv4  |
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Description changed by mascguy:

Old description:

> Now that the two OpenCV-related ports have been brought up to parity,
> there are very few differences between them. Eliminate the portfile
> duplication, via subports.
>
> Other notable cleanup that will be tackled during the reconciliation:
> * Universal use of `github` portgroup. Currently used for opencv4, but
> not for opencv3.
> * Adopt `cmake` portgroup, to reduce number of CMake flags needed.
> * If supported by OpenCV, simplify Python subports to generate Python
> bindings from built libs, rather than having to rebuild entire library.

New description:

 Now that the two OpenCV-related ports have been brought up to parity,
 there are very few differences between them. Eliminate the portfile
 duplication, via subports.

 Other notable cleanup that will be tackled during the reconciliation:
 * Universal use of `github` portgroup. Currently used for opencv4, but not
 for opencv3.
 * Adopt `cmake` portgroup, to reduce number of CMake flags needed.
 * If supported by OpenCV, streamline Python binding generation: Do so from
 the built libs, rather than rebuilding entire library.

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Ticket URL: <https://trac.macports.org/ticket/62011#comment:14>
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