Allow selecting features in the CMake integration

Provide the same features as in the Rust API crate, as CMake
options.

api/sixtyfps-cpp/CMakeLists.txt

@@ -14,7 +14,7 @@ include(FetchContent)
 FetchContent_Declare(
     Corrosion
     GIT_REPOSITORY https://github.com/AndrewGaspar/corrosion.git
-    GIT_TAG b7a78deb2632b502717c7b636a925677a99e06a1
+    GIT_TAG 9ea8f6ba30750926b622bab6d4c89b8ab78abe04
 )
 FetchContent_MakeAvailable(Corrosion)
 corrosion_import_crate(MANIFEST_PATH "${CMAKE_CURRENT_SOURCE_DIR}/../../Cargo.toml"
@@ -59,6 +59,39 @@ add_library(SixtyFPS::SixtyFPS ALIAS SixtyFPS)
 target_link_libraries(SixtyFPS INTERFACE sixtyfps-cpp)
 target_compile_features(SixtyFPS INTERFACE cxx_std_17)
 
+if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.19.0)
+    function(define_cargo_feature cargo-feature description default)
+        # turn foo-bar into SIXTYFPS_FEATURE_FOO_BAR
+        string(TOUPPER "${cargo-feature}" cmake_option)
+        string(REPLACE "-"  "_" cmake_option "${cmake_option}")
+        set(cmake_option "SIXTYFPS_FEATURE_${cmake_option}")
+        option("${cmake_option}" "${description}" ${default})
+        if(${cmake_option})
+            list(APPEND features ${cargo-feature})
+        endif()
+        set(features "${features}" PARENT_SCOPE)
+    endfunction()
+
+    # Features that are mapped to features in the Rust crate. These and their
+    # defaults need to be kept in sync with the Rust bit.
+    define_cargo_feature(interpreter "Enable support for the SixtyFPS interpeter to load .60 files at run-time" ON)
+    define_cargo_feature(x11 "Enable X11 support when using GL backend" ON)
+    define_cargo_feature(wayland "Enable Wayland support when using the GL backend" OFF)
+    define_cargo_feature(backend-gl "Enable OpenGL ES 2.0 based rendering backend" ON)
+    define_cargo_feature(backend-qt "Enable Qt based rendering backend" ON)
+
+    set_property(
+        TARGET sixtyfps-cpp
+        PROPERTY CORROSION_FEATURES
+        ${features}    
+    )
+    set_property(
+        TARGET sixtyfps-cpp
+        PROPERTY CORROSION_NO_DEFAULT_FEATURES
+        ${features}    
+    )    
+endif()
+
 file(GLOB api_headers RELATIVE "${CMAKE_CURRENT_SOURCE_DIR}/include/"
     "${CMAKE_CURRENT_SOURCE_DIR}/include/*.h")
 

api/sixtyfps-cpp/Cargo.toml

@@ -13,10 +13,14 @@ publish = false
 path = "lib.rs"
 crate-type = ["lib", "cdylib"]
 
+# Note, these features need to be kept in sync (along with their defaults) in
+# the C++ crate's CMakeLists.txt
 [features]
-# In the future, this shouldn't be a default feature, but should be enabled by cmake
-default = ["sixtyfps-interpreter"]
-
+interpreter = ["sixtyfps-interpreter"]
+x11 = ["sixtyfps-rendering-backend-default/x11"]
+wayland = ["sixtyfps-rendering-backend-default/wayland"]
+backend-gl = ["sixtyfps-rendering-backend-default/sixtyfps-rendering-backend-gl"]
+backend-qt = ["sixtyfps-rendering-backend-default/sixtyfps-rendering-backend-qt"]
 # Enable some function used by the integration tests
 testing = ["sixtyfps-rendering-backend-testing"]
 

api/sixtyfps-cpp/docs/cmake.md

@@ -34,6 +34,24 @@ FetchContent_MakeAvailable(SixtyFPS)
 If you prefer to treat SixtyFPS as an external CMake package, then you can also build SixtyFPS from source like a regular
 CMake project, install it into a prefix directory of your choice and use `find_package(SixtyFPS)` in your `CMakeLists.txt`.
 
+### Features
+
+The SixtyFPS run-time library supports different features that can be toggled. You might want to enable a feature that is
+not enabled by default but that is revelant for you, or you may want to disable a feature that you know you do not need and
+therefore reduce the size of the resulting library.
+
+The CMake configure step offers CMake options for various feature that are all prefixed with `SIXTYFPS_FEATURE_`. For example
+you can enable support for the Wayland windowing system on Linux by enabling the `SIXTYFPS_FEATURE_WAYLAND` feature. There are
+different ways of toggling CMake options. For example on the command line using the `-D` parameter:
+
+   `cmake -DSIXTYFPS_FEATURE_WAYLAND=ON ...`
+
+Alternatively, after the configure step you can use `cmake-gui` or `ccmake` on the build directory for a list of all features
+and their description.
+
+This works when compiling SixtyFPS as a package, using `cmake --build` and `cmake --install`, or when including SixtyFPS
+using `FetchContent`.
+
 ### Cross-compiling
 
 It is possible to cross-compile SixtyFPS to a different target architecture when building with CMake. In order to complete