Compiler and linker flags in Rcpp: Magick++ - c++

Question

I have an R script, which loads an Rcpp file. The Rcpp file needs the magick++ library, so I used:
#include <Rcpp.h>
#include <Magick++.h>
However when I run the script, I get:
fatal error: Magick++.h: No such file or directory
The library libmagick++-dev is installed.
How can I include Magick++ in an Rcpp file? How can I compile it with flags? For instance:
-DHAVE_CONFIG_H, -DMAGICKCORE_QUANTUM_DEPTH=16, -DMAGICKCORE_HDRI_ENABLE=0
A minimal working example:
mwe.r
library(Rcpp)
sourceCpp("./mwe.cpp")
mwe.cpp
#include <Rcpp.h>
#include <Magick++.h>
//[[Rcpp::plugins(cpp11)]]

Answer 1

As #hrbrmstr mentions, there is a CRAN package magick that provides ImageMagick functionality already; maybe that avoids the need to do anything yourself?
From these ImageMagick instructions you can see that a C++ program needs to know about compiler flags (the output of Magick++-config --cppflags --cxxflags) and linker flags (Magick++-config --ldflags --libs).
The best way to compile Rcpp code with complicated compilation and linkage steps is (I'm no expert here...) to create an Rcpp package
/tmp$ Rdev --vanilla -e "Rcpp::Rcpp.package.skeleton('Magick')"
/tmp$ cd Magick
I edited Magick/src/rcpp_hello_world.cpp to
#include <Rcpp.h>
#include <Magick++.h>
using namespace Rcpp;
// [[Rcpp::export]]
LogicalVector rcpp_hello_world()
{
Magick::InitializeMagick("RcppMagick");
return true;
}
And added package pre-processing, compilation, and linkage commands (following Writing R Extensions, available via RShowDoc("R-exts")) to a new file Magick/src/Makevars like
PKG_CPPFLAGS = `Magick++-config --cppflags`
PKG_CXXFLAGS = `Magick++-config --cxxflags`
PKG_LIBS = `Magick++-config --ldflags --libs`
I then updated the attributes of my package, installed it, and verified that it could be used
/tmp/Magick master$ Rdev --vanilla -e "Rcpp::compileAttributes()"
> Rcpp::compileAttributes()
>
>
/tmp/Magick master$ Rdev --vanilla CMD INSTALL .
* installing to library ...‘/home/mtmorgan/R/x86_64-pc-linux-gnu-library/3.5-Bioc-3.7’
* installing *source* package ‘Magick’ ...
** libs
g++ -I"/home/mtmorgan/bin/R-devel/include" -DNDEBUG `Magick++-config --cppflags` -I"/home/mtmorgan/R/x86_64-pc-linux-gnu-library/3.5-Bioc-3.7/Rcpp/include" -I/usr/local/include `Magick++-config --cxxflags` -fpic -g -O3 -Wall -pedantic -c RcppExports.cpp -o RcppExports.o
g++ -I"/home/mtmorgan/bin/R-devel/include" -DNDEBUG `Magick++-config --cppflags` -I"/home/mtmorgan/R/x86_64-pc-linux-gnu-library/3.5-Bioc-3.7/Rcpp/include" -I/usr/local/include `Magick++-config --cxxflags` -fpic -g -O3 -Wall -pedantic -c rcpp_hello_world.cpp -o rcpp_hello_world.o
g++ -shared -L/usr/local/lib -o Magick.so RcppExports.o rcpp_hello_world.o -L/usr/lib -L/usr/lib/X11 -lGraphicsMagick++ -lGraphicsMagick -ljbig -lwebp -llcms2 -ltiff -lfreetype -ljasper -ljpeg -lpng12 -lwmflite -lXext -lSM -lICE -lX11 -llzma -lbz2 -lxml2 -lz -lm -lgomp -lpthread
installing to /home/mtmorgan/R/x86_64-pc-linux-gnu-library/3.5-Bioc-3.7/Magick/libs
...
/tmp/Magick master$ Rdev --vanilla -e "Magick::rcpp_hello_world()"
> Magick::rcpp_hello_world()
[1] TRUE
I had to figure out what system package to install to get Magick++-config. When I first tried to install my package R complained that it didn't know about -lwebp, so I installed that system dependency too (libwebp-dev). The package would be good enough for personal use, but would need to be more robust for cross-platform or production use. There could be many problems encountered while trying to integrate this complicated library into R.