Expand CMake documentation a bit (#5961)

* cmake: remove duplicate check_required_components macro

* Expand docs/README-cmake.md a bit

* cmake: path needs `/` infix

docs/README-cmake.md

@@ -1,40 +1,102 @@
-CMake
-================================================================================
+# CMake
+
 (www.cmake.org)
 
 SDL's build system was traditionally based on autotools. Over time, this
 approach has suffered from several issues across the different supported 
 platforms.
-To solve these problems, a new build system based on CMake is under development.
-It works in parallel to the legacy system, so users can experiment with it
-without complication.
-While still experimental, the build system should be usable on the following
-platforms:
+To solve these problems, a new build system based on CMake was introduced.
+It is developed in parallel to the legacy autotools build system, so users 
+can experiment with it without complication.
+
+The CMake build system is supported on the following platforms:
 
 * FreeBSD
 * Linux
-* VS.NET 2010
+* Microsoft Visual C
 * MinGW and Msys
 * macOS, iOS, and tvOS, with support for XCode
+* Android
+* Emscripten
+* RiscOS
+* Playstation Vita
+
+## Building SDL
+
+Assuming the source for SDL is located at `~/sdl`
+```sh
+cd ~
+mkdir build
+cd build
+cmake ~/sdl
+cmake --build .
+```
+
+This will build the static and dynamic versions of SDL in the `~/build` directory.
+Installation can be done using:
+
+```sh
+cmake --install .        # '--install' requires CMake 3.15, or newer
+```
+
+## Including SDL in your project
+
+SDL can be included in your project in 2 major ways:
+- using a system SDL library, provided by your (*nix) distribution or a package manager
+- using a vendored SDL library: this is SDL copied or symlinked in a subfolder.
+
+The following CMake script supports both, depending on the value of `MYGAME_VENDORED`.
 
+```cmake
+cmake_minimum_required(VERSION 3.0)
+project(mygame)
 
-================================================================================
-Usage
-================================================================================
+# Create an option to switch between a system sdl library and a vendored sdl library
+option(MYGAME_VENDORED "Use vendored libraries" OFF)
 
-Assuming the source for SDL is located at ~/sdl
+if(MYGAME_VENDORED)
+    add_subdirectory(vendored/sdl EXCLUDE_FROM_ALL)
+else()
+    # 1. Look for a SDL2 package, 2. look for the SDL2 component and 3. fail if none can be found
+    find_package(SDL2 REQUIRED CONFIG REQUIRED COMPONENTS SDL2)
+    
+    # 1. Look for a SDL2 package, 2. Look for the SDL2maincomponent and 3. DO NOT fail when SDL2main is not available 
+    find_package(SDL2 REQUIRED CONFIG COMPONENTS SDL2main)
+endif()
 
-    cd ~
-    mkdir build
-    cd build
-    cmake ../sdl
+# Create your game executable target as usual 
+add_executable(mygame WIN32 mygame.c)
 
-This will build the static and dynamic versions of SDL in the ~/build directory.
+# SDL2::SDL2main may or may not be available. It is e.g. required by Windows GUI applications  
+if(TARGET SDL2::SDL2main)
+    # It has an implicit dependency on SDL2 functions, so it MUST be added before SDL2::SDL2 (or SDL2::SDL2-static)
+    target_link_libraries(mygame PRIVATE SDL2::SDL2main)
+endif()
 
+# Link to the actual SDL2 library. SDL2::SDL2 is the shared SDL library, SDL2::SDL2-static is the static SDL libarary.
+target_link_libraries(mygame PRIVATE SDL2::SDL2)
+```
 
-================================================================================
-Usage, iOS/tvOS
-================================================================================
+### A system SDL library
+
+For CMake to find SDL, it must be installed in [a default location CMake is looking for](https://cmake.org/cmake/help/latest/command/find_package.html#config-mode-search-procedure).
+
+The following components are available, to be used as an argument of `find_package`.
+
+| Component name | Description                                                                                |
+|----------------|--------------------------------------------------------------------------------------------|
+| SDL2           | The SDL2 shared library, available through the `SDL2::SDL2` target [^SDL_TARGET_EXCEPTION] |
+| SDL2-static    | The SDL2 static library, available through the `SDL2::SDL2-static` target                  |
+| SDL2main       | The SDL2main static library, available through the `SDL2::SDL2main` target                 |
+| SDL2test       | The SDL2test static library, available through the `SDL2::SDL2test` target                 |
+
+### Using a vendored SDL
+
+This only requires a copy of SDL in a subdirectory.
+
+## CMake configuration options for platforms
+
+### iOS/tvOS
 
 CMake 3.14+ natively includes support for iOS and tvOS.  SDL binaries may be built
 using Xcode or Make, possibly among other build-systems.
@@ -53,32 +115,49 @@ To use, set the following CMake variables when running CMake's configuration sta
 - `CMAKE_OSX_ARCHITECTURES=<semicolon-separated list of CPU architectures>` (example: "arm64;armv7s;x86_64")
 
 
-### Examples (for iOS/tvOS):
+#### Examples
 
 - for iOS-Simulator, using the latest, installed SDK:
 
-    `cmake ~/sdl -DCMAKE_SYSTEM_NAME=iOS -DCMAKE_OSX_SYSROOT=iphonesimulator -DCMAKE_OSX_ARCHITECTURES=x86_64`
+    ```bash
+    cmake ~/sdl -DCMAKE_SYSTEM_NAME=iOS -DCMAKE_OSX_SYSROOT=iphonesimulator -DCMAKE_OSX_ARCHITECTURES=x86_64
+    ```
 
 - for iOS-Device, using the latest, installed SDK, 64-bit only
 
-    `cmake ~/sdl -DCMAKE_SYSTEM_NAME=iOS -DCMAKE_OSX_SYSROOT=iphoneos -DCMAKE_OSX_ARCHITECTURES=arm64`
+    ```bash
+    cmake ~/sdl -DCMAKE_SYSTEM_NAME=iOS -DCMAKE_OSX_SYSROOT=iphoneos -DCMAKE_OSX_ARCHITECTURES=arm64
+    ```
 
 - for iOS-Device, using the latest, installed SDK, mixed 32/64 bit
 
-    `cmake ~/sdl -DCMAKE_SYSTEM_NAME=iOS -DCMAKE_OSX_SYSROOT=iphoneos -DCMAKE_OSX_ARCHITECTURES="arm64;armv7s"`
+    ```cmake
+    cmake ~/sdl -DCMAKE_SYSTEM_NAME=iOS -DCMAKE_OSX_SYSROOT=iphoneos -DCMAKE_OSX_ARCHITECTURES="arm64;armv7s"
+    ```
 
 - for iOS-Device, using a specific SDK revision (iOS 12.4, in this example):
 
-    `cmake ~/sdl -DCMAKE_SYSTEM_NAME=iOS -DCMAKE_OSX_SYSROOT=iphoneos12.4 -DCMAKE_OSX_ARCHITECTURES=arm64`
+    ```cmake
+    cmake ~/sdl -DCMAKE_SYSTEM_NAME=iOS -DCMAKE_OSX_SYSROOT=iphoneos12.4 -DCMAKE_OSX_ARCHITECTURES=arm64
+    ```
 
 - for iOS-Simulator, using the latest, installed SDK, and building SDL test apps (as .app bundles):
 
-    `cmake ~/sdl -DSDL_TESTS=1 -DCMAKE_SYSTEM_NAME=iOS -DCMAKE_OSX_SYSROOT=iphonesimulator -DCMAKE_OSX_ARCHITECTURES=x86_64`
+    ```cmake
+    cmake ~/sdl -DSDL_TESTS=1 -DCMAKE_SYSTEM_NAME=iOS -DCMAKE_OSX_SYSROOT=iphonesimulator -DCMAKE_OSX_ARCHITECTURES=x86_64
+    ```
 
 - for tvOS-Simulator, using the latest, installed SDK:
 
-    `cmake ~/sdl -DCMAKE_SYSTEM_NAME=tvOS -DCMAKE_OSX_SYSROOT=appletvsimulator -DCMAKE_OSX_ARCHITECTURES=x86_64`
+    ```cmake
+    cmake ~/sdl -DCMAKE_SYSTEM_NAME=tvOS -DCMAKE_OSX_SYSROOT=appletvsimulator -DCMAKE_OSX_ARCHITECTURES=x86_64
+    ```
 
 - for tvOS-Device, using the latest, installed SDK:
 
-    `cmake ~/sdl -DCMAKE_SYSTEM_NAME=tvOS -DCMAKE_OSX_SYSROOT=appletvos -DCMAKE_OSX_ARCHITECTURES=arm64`
+    ```cmake
+    cmake ~/sdl -DCMAKE_SYSTEM_NAME=tvOS -DCMAKE_OSX_SYSROOT=appletvos -DCMAKE_OSX_ARCHITECTURES=arm64`
+    ```
+
+
+[^SDL_TARGET_EXCEPTION]: `SDL2::SDL2` can be an ALIAS to a static `SDL2::SDL2-static` target for multiple reasons.

sdl2-config.cmake.in

@@ -14,18 +14,8 @@ macro(set_and_check _var _file)
     endif()
 endmacro()
 
-# Copied from `configure_package_config_file`
-macro(check_required_components _NAME)
-    foreach(comp ${${_NAME}_FIND_COMPONENTS})
-        if(NOT ${_NAME}_${comp}_FOUND)
-            if(${_NAME}_FIND_REQUIRED_${comp})
-                set(${_NAME}_FOUND FALSE)
-            endif()
-        endif()
-    endforeach()
-endmacro()
-
 get_filename_component(prefix "${CMAKE_CURRENT_LIST_DIR}/@cmake_prefix_relpath@" ABSOLUTE)
+
 set(exec_prefix "@exec_prefix@")
 set(bindir "@bindir@")
 set(libdir "@libdir@")