add function to load raster from QGIS layer

CMakeLists.txt

@@ -194,6 +194,21 @@ if(WITH_CORE)
     endif()
   endif()
 
+  set (WITH_R FALSE CACHE BOOL "Determines whether the inbuilt R integration should be built")
+  if(WITH_R)
+    find_package(R)
+    if (NOT ${R_FOUND})
+      message(FATAL_ERROR "R library not found")
+    endif()
+
+    find_package(RCpp)
+    if (NOT ${RCpp_FOUND})
+      message(FATAL_ERROR "Rcpp library not found")
+    endif()
+
+    set(HAVE_R TRUE)  # used in qgisconfig.h
+  endif()
+
   # server disabled default because it needs FastCGI (which is optional dependency)
   set (WITH_SERVER FALSE CACHE BOOL "Determines whether QGIS server should be built")
   if(WITH_SERVER)

cmake/FindR.cmake

@@ -0,0 +1,40 @@
+# CMake module to search for R
+#
+# Once done this will define
+#
+#  R_FOUND - system has the R library
+#  R_INCLUDE_DIR - the R library include directories
+#  R_LIB - the R library
+#
+# Copyright (c) 2022, Nyall Dawson, <nyall dot dawson at gmail dot com>
+#
+# Redistribution and use is allowed according to the terms of the BSD license.
+# For details see the accompanying COPYING-CMAKE-SCRIPTS file.
+
+execute_process(COMMAND R CMD config --cppflags OUTPUT_VARIABLE R_INCLUDE_DIR_TMP)
+string(REGEX REPLACE "^-I" "" R_INCLUDE_DIR_TMP "${R_INCLUDE_DIR_TMP}")
+string(STRIP ${R_INCLUDE_DIR_TMP} R_INCLUDE_DIR_TMP)
+set(R_INCLUDE_DIR "${R_INCLUDE_DIR_TMP}" CACHE STRING INTERNAL)
+
+#message(STATUS "Found R include dirs: ${R_INCLUDE_DIR}")
+
+execute_process(COMMAND R CMD config --ldflags OUTPUT_VARIABLE R_LDFLAGS)
+if (${R_LDFLAGS} MATCHES "[-][L]([^ ;])+")
+    string(SUBSTRING ${CMAKE_MATCH_0} 2 -1 R_LIB_DIR)
+    string(STRIP ${R_LIB_DIR} R_LIB_DIR)
+    find_library(R_LIB
+      NAMES libR.so PATHS
+      "${R_LIB_DIR}"
+    )
+endif()
+
+INCLUDE(FindPackageHandleStandardArgs)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(R DEFAULT_MSG
+                                  R_LIB R_INCLUDE_DIR)
+
+if(R_FOUND)
+  message(STATUS "Found R library: ${R_LIB}")
+endif()
+
+mark_as_advanced(R_INCLUDE_DIR)
+mark_as_advanced(R_LIB)

cmake/FindRCpp.cmake

@@ -0,0 +1,39 @@
+# CMake module to search for RCpp
+#
+# Once done this will define
+#
+#  RCpp_FOUND - system has the RCpp library
+#  RCpp_INCLUDE_DIR - the RCpp library include directories
+#  RCpp_LIB - the RCpp library
+#
+# Copyright (c) 2022, Nyall Dawson, <nyall dot dawson at gmail dot com>
+#
+# Redistribution and use is allowed according to the terms of the BSD license.
+# For details see the accompanying COPYING-CMAKE-SCRIPTS file.
+
+execute_process(COMMAND Rscript -e "Rcpp:::CxxFlags()"
+                OUTPUT_VARIABLE RCpp_INCLUDE_DIR_TMP)
+string(REGEX REPLACE "^-I" "" RCpp_INCLUDE_DIR_TMP "${RCpp_INCLUDE_DIR_TMP}")
+string(STRIP ${RCpp_INCLUDE_DIR_TMP} RCpp_INCLUDE_DIR_TMP )
+string(REGEX REPLACE "^\"" "" RCpp_INCLUDE_DIR_TMP "${RCpp_INCLUDE_DIR_TMP}")
+string(REGEX REPLACE "\"$" "" RCpp_INCLUDE_DIR_TMP "${RCpp_INCLUDE_DIR_TMP}")
+set(RCpp_INCLUDE_DIR "${RCpp_INCLUDE_DIR_TMP}" CACHE STRING INTERNAL)
+
+find_library(RCpp_LIB
+  NAMES Rcpp.so PATHS
+  "${RCpp_INCLUDE_DIR}/../libs"
+)
+
+INCLUDE(FindPackageHandleStandardArgs)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(RCpp DEFAULT_MSG
+                                  RCpp_LIB RCpp_INCLUDE_DIR)
+
+if(RCpp_FOUND)
+  message(STATUS "Found Rcpp library: ${RCpp_LIB}")
+endif()
+
+add_library(Rcpp UNKNOWN IMPORTED)
+set_property(TARGET Rcpp PROPERTY IMPORTED_LOCATION "${RCpp_LIB}")
+
+mark_as_advanced(RCpp_INCLUDE_DIR)
+mark_as_advanced(RCpp_LIB)

cmake_templates/qgsconfig.h.in

@@ -116,5 +116,7 @@
 
 #cmakedefine HAVE_CRASH_HANDLER
 
+#cmakedefine HAVE_R
+
 #endif
 

external/r_inside/README.md

@@ -0,0 +1,62 @@
+## RInside: Easy embedding of R inside C++ (and C)
+
+[![CI](https://github.com/eddelbuettel/rinside/workflows/ci/badge.svg)](https://github.com/eddelbuettel/rinside/actions?query=workflow%3Aci)
+[![License](http://img.shields.io/badge/license-GPL%20%28%3E=%202%29-brightgreen.svg?style=flat)](http://www.gnu.org/licenses/gpl-2.0.html)
+[![CRAN](http://www.r-pkg.org/badges/version/RInside)](https://cran.r-project.org/package=RInside)
+[![Dependencies](https://tinyverse.netlify.com/badge/RInside)](https://cran.r-project.org/package=RInside)
+[![Debian package](https://img.shields.io/debian/v/r-cran-rinside/sid?color=brightgreen)](https://packages.debian.org/sid/r-cran-rinside)
+[![Downloads](http://cranlogs.r-pkg.org/badges/RInside?color=brightgreen)](https://cran.r-project.org/package=RInside)
+[![Last Commit](https://img.shields.io/github/last-commit/eddelbuettel/rinside)](https://github.com/eddelbuettel/rinside)
+
+### About
+
+The RInside package provides a few classes for seamless embedding of [R](https://www.r-project.org) inside of
+C++ applications by relying on [Rcpp](https://www.rcpp.org/).
+
+### Examples
+
+Provided with the package itself are nine subdirectories with examples: from more than a dozen basic command-line examples (in directory
+`standard`) to graphical user-interfaces (using both [Qt](https://www.qt.io/) and [Wt](https://www.webtoolkit.eu/wt)), linear algebra with
+[Armadillo](http://arma.sourceforge.net/) and [Eigen](http://eigen.tuxfamily.org/index.php?title=Main_Page), parallel computing with MPI to a
+sandboxed server, and (since release 0.2.16) a simple (and more limited) interface for embedding insice C applications.
+
+The simplest example (modulo its header) is [examples/standard/rinside_sample0.cpp](inst/examples/standard/rinside_sample0.cpp)
+
+```c++
+#include <RInside.h>                    // for the embedded R via RInside
+
+int main(int argc, char *argv[]) {
+
+    RInside R(argc, argv);              // create an embedded R instance
+
+    R["txt"] = "Hello, world!\n";	    // assign a char* (string) to 'txt'
+
+    R.parseEvalQ("cat(txt)");           // eval the init string, ignoring any returns
+
+    exit(0);
+}
+```
+The [Qt example directory](https://github.com/eddelbuettel/rinside/tree/master/inst/examples/qt) produces
+this application for showing how to use R (to estimate densities) inside a C++ executable (providing the GUI):
+
+![](https://github.com/eddelbuettel/rinside/blob/master/local/qtdensitySVG.png)
+
+The code is portable across operating systems.  Similar, the
+[Wt example directory](https://github.com/eddelbuettel/rinside/tree/master/inst/examples/wt)
+contains this C++-based web application doing the same:
+
+![](https://github.com/eddelbuettel/rinside/blob/master/local/wtdensity.png)
+
+
+### See Also
+
+The [RInside](http://dirk.eddelbuettel.com/code/rinside.html) web page has
+some more details.
+
+### Authors
+
+Dirk Eddelbuettel, Romain Francois, and Lance Bachmeier
+
+### License
+
+GPL (>= 2)