Makes the example that requires libgbm optional

CMakeLists.txt

@@ -213,6 +213,10 @@ endif(BUILD_EXAMPLES)
 # Additional examples (requires BUILD_EXAMPLES ON)
 option(BUILD_DOC_SCREENSHOTS "Build documentation screenshot examples" OFF)
 
+# Some examples may require additional dependencies such as libgbm that can't be detected via
+# a typical find_package() call. Make these optional with a cmake flag.
+option(BUILD_OPTIONAL_EXAMPLES "Build examples that require additional non-find_package-able dependencies" OFF)
+
 # first we can indicate the documentation build as an option and set it to ON by default
 option(BUILD_DOC "Build documentation" OFF)
 if(BUILD_DOC)

README.build.linux.md

@@ -27,14 +27,14 @@ sudo apt install build-essential cmake git \
 ```
 For the optional dependencies it's:
 ```sh
-sudo apt install libarmadillo-dev libhdf5-dev qtcreator qtbase5-dev libwxgtk3.2-dev libgbm-dev libegl-dev
+sudo apt install libarmadillo-dev libhdf5-dev qtcreator qtbase5-dev libwxgtk3.2-dev libegl-dev libgbm-dev
 ```
 * Armadillo. Only required if you use the ```sm::bezcurve``` class.
-* HDF5 library. Required if you use the wrapper class ```sm::hdfdata``` or any of the classes that make use of HdfData (```sm::hexgrid```,```sm::cartgrid```,```sm::anneal```). Their tests and examples should all compile if the libraries are detected and be omitted if not.
+* HDF5 library. Required if you use the wrapper class ```sm::hdfdata``` or any of the classes that make use of `sm::hdfdata` (```sm::hexgrid```,```sm::cartgrid```,```sm::anneal```). Their tests and examples should all compile if the libraries are detected and be omitted if not.
 * Qt library. Installing qtcreator will bring in the Qt5 libraries that are used to compile some Qt-mathplot example programs. It almost certainly possible to install *only* the Qt5 Core, Gui and Widgets libraries, but that hasn't been verified. On recent Ubuntu systems, you may well need qtbase5-dev to get the cmake scripts to `find_package(Qt5...)`.
 * WxWindows. libwxgtk3.2-dev (you'll need Ubuntu 23.04+) will enable the compilation of mathplot-wxWidgets example programs.
+* EGL. Required to build GLES applications that are compatible with Raspberry Pi 4 and 5.
 * GBM. Required only for window-less OpenGL compute compilations. Currently that's one example program only.
-* EGL. Requried to build GLES applications that are compatible with Raspberry Pi 4 and 5.
 
 ### Package-managed dependencies for Arch Linux
 
@@ -75,6 +75,8 @@ cmake .. -DBUILD_TESTS=ON -DBUILD_EXAMPLES=OFF # Build tests but not examples
 # ...etc
 ```
 
+There is also the flag `BUILD_OPTIONAL_EXAMPLES` to enable any programs that use additional dependencies that can't be tested for in the base `CMakeLists.txt`. Currently, that's just one example that uses libgbm.
+
 If you need to build the test programs with a specific compiler, such
 as g++-11 or clang, then you just change the cmake call in the recipe
 above. It becomes:

examples/gl_compute/CMakeLists.txt

@@ -13,8 +13,13 @@ if (OpenGL_EGL_FOUND)
   add_executable(shader_naive_scan shader_naive_scan.cpp)
   target_link_libraries(shader_naive_scan OpenGL::EGL glfw)
 
-  add_executable(shader_naive_scan_cli shader_naive_scan_cli.cpp)
-  target_link_libraries(shader_naive_scan_cli OpenGL::EGL gbm)
+  # This example requires the user to install libgbm (`sudo apt
+  # install libgbm-dev` on Debian-like Linux). Because gbm can't be
+  # detected wtih find_package, there's an extra option flag for it.
+  if(BUILD_OPTIONAL_EXAMPLES)
+    add_executable(shader_naive_scan_cli shader_naive_scan_cli.cpp)
+    target_link_libraries(shader_naive_scan_cli OpenGL::EGL gbm)
+  endif()
 
   add_executable(seq_naive_scan naive_scan.cpp)
 endif (OpenGL_EGL_FOUND)