Always link OpenGL libs, also add option to build with GLES3

As libprojectM 4.2 and higher will use a dedicated GL loader and no longer pass down the GL dependency (so apps can choose their own implementation), linking GL is now required explicitly. Won't break older versions though.

Also added a ENABLE_GLES CMake option to build the application with GLES 3.2 support, making it easier to build it on devices such as the Raspberry Pi. Affects both SDL GL initialization and the ImGui-internal GL loader. libprojectM needs to be built accordingly of course.

Author: kblaschke

CMakeLists.txt

@@ -15,6 +15,7 @@ list(APPEND CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake")
 
 option(ENABLE_FLAT_PACKAGE "Creates a \"flat\" install layout with the executable, configuration file(s) and preset/texture dirs directly in the install prefix." OFF)
 option(ENABLE_INSTALL_BDEPS "Installs all shared libraries projectMSDL requires to run. On some platforms, CMake 3.31 or higher is required for this to work!" OFF)
+option(ENABLE_GLES "Build the application to use OpenGL ES instead of Core GL. May not work on all platforms and requires CMake 3.27 or higher." OFF)
 
 set(PROJECTMSDL_PROPERTIES_FILENAME "projectMSDL.properties")
 
@@ -97,6 +98,14 @@ endif()
 
 find_package(projectM4 REQUIRED COMPONENTS Playlist)
 find_package(SDL2 REQUIRED)
+if (NOT ENABLE_GLES)
+    find_package(OpenGL REQUIRED)
+else ()
+    if (CMAKE_VERSION VERSION_LESS 3.27)
+        message(FATAL_ERROR "CMake 3.27 or higher is required to build with OpenGL ES 3!")
+    endif ()
+    find_package(OpenGL REQUIRED COMPONENTS GLES3)
+endif()
 find_package(Poco REQUIRED COMPONENTS JSON XML Util Foundation)
 
 if(Poco_VERSION VERSION_GREATER_EQUAL 1.14.0)

ImGui.cmake

@@ -42,6 +42,13 @@ target_include_directories(ImGui
         ${SDL2_INCLUDE_DIRS}
         )
 
+if (ENABLE_GLES)
+    target_compile_definitions(ImGui
+            PUBLIC
+            IMGUI_IMPL_OPENGL_ES3
+            )
+endif ()
+
 # Build font embedding tool
 add_executable(ImGuiBinaryToCompressedC EXCLUDE_FROM_ALL
         vendor/imgui/misc/fonts/binary_to_compressed_c.cpp

src/CMakeLists.txt

@@ -34,6 +34,13 @@ set_target_properties(projectMSDL PROPERTIES
         MACOSX_BUNDLE_INFO_PLIST "${CMAKE_CURRENT_SOURCE_DIR}/resources/Info.plist.in"
         )
 
+if (ENABLE_GLES)
+    target_compile_definitions(projectMSDL
+            PUBLIC
+            USE_GLES
+            )
+endif ()
+
 if (CMAKE_SYSTEM_NAME STREQUAL "Windows")
     target_sources(projectMSDL
             PRIVATE
@@ -56,7 +63,7 @@ else ()
             )
 endif ()
 
-# GLEW needs to be initialized if libprojectM depends on it.
+# GLEW needs to be initialized if libprojectM depends on it (<v4.2).
 if (TARGET GLEW::glew OR TARGET GLEW::glew_s)
     target_compile_definitions(projectMSDL
             PRIVATE
@@ -81,6 +88,7 @@ target_link_libraries(projectMSDL
         Poco::Util
         SDL2::SDL2$<$<STREQUAL:${SDL2_LINKAGE},static>:-static>
         SDL2::SDL2main
+        OpenGL::$<IF:$<BOOL:${ENABLE_GLES}>,GLES3,GL>
         )
 
 if (MSVC)

src/SDLRenderingWindow.cpp

@@ -238,9 +238,9 @@ void SDLRenderingWindow::CreateSDLWindow()
     }
 
 #if USE_GLES
-    // use GLES 2.0
-    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
-    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
+    // use GLES 3.2
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
 #else
     // projectM Requires at least Core Profile 3.30 for samplers etc.