Remove direct OpenGL(ES) dependency

IrrlichtMt now provides this for us (see last commit)
fixes #12041

README.md

@@ -249,7 +249,7 @@ General options and their default values:
     ENABLE_CURL=ON             - Build with cURL; Enables use of online mod repo, public serverlist and remote media fetching via http
     ENABLE_CURSES=ON           - Build with (n)curses; Enables a server side terminal (command line option: --terminal)
     ENABLE_GETTEXT=ON          - Build with Gettext; Allows using translations
-    ENABLE_GLES=OFF            - Build for OpenGL ES instead of OpenGL (requires support by IrrlichtMt)
+    ENABLE_GLES=OFF            - Enable extra support code for OpenGL ES (requires support by IrrlichtMt)
     ENABLE_LEVELDB=ON          - Build with LevelDB; Enables use of LevelDB map backend
     ENABLE_POSTGRESQL=ON       - Build with libpq; Enables use of PostgreSQL map backend (PostgreSQL 9.5 or greater recommended)
     ENABLE_REDIS=ON            - Build with libhiredis; Enables use of Redis map backend
@@ -259,7 +259,6 @@ General options and their default values:
     ENABLE_PROMETHEUS=OFF      - Build with Prometheus metrics exporter (listens on tcp/30000 by default)
     ENABLE_SYSTEM_GMP=ON       - Use GMP from system (much faster than bundled mini-gmp)
     ENABLE_SYSTEM_JSONCPP=ON   - Use JsonCPP from system
-    OPENGL_GL_PREFERENCE=LEGACY - Linux client build only; See CMake Policy CMP0072 for reference
     RUN_IN_PLACE=FALSE         - Create a portable install (worlds, settings etc. in current directory)
     USE_GPROF=FALSE            - Enable profiling using GProf
     VERSION_EXTRA=             - Text to append to version (e.g. VERSION_EXTRA=foobar -> Minetest 0.4.9-foobar)
@@ -300,8 +299,6 @@ Library specific options:
     OPENAL_DLL                      - Only if building with sound on Windows; path to OpenAL32.dll
     OPENAL_INCLUDE_DIR              - Only if building with sound; directory where al.h is located
     OPENAL_LIBRARY                  - Only if building with sound; path to libopenal.a/libopenal.so/OpenAL32.lib
-    OPENGLES2_INCLUDE_DIR           - Only if building with GLES; directory that contains gl2.h
-    OPENGLES2_LIBRARY               - Only if building with GLES; path to libGLESv2.a/libGLESv2.so
     SQLITE3_INCLUDE_DIR             - Directory that contains sqlite3.h
     SQLITE3_LIBRARY                 - Path to libsqlite3.a/libsqlite3.so/sqlite3.lib
     VORBISFILE_LIBRARY              - Only if building with sound; path to libvorbisfile.a/libvorbisfile.so/libvorbisfile.dll.a

cmake/Modules/FindOpenGLES2.cmake

@@ -1,73 +0,0 @@
-#-------------------------------------------------------------------
-# The contents of this file are placed in the public domain. Feel
-# free to make use of it in any way you like.
-#-------------------------------------------------------------------
-
-# - Try to find OpenGLES and EGL
-# Once done this will define
-#
-#  OPENGLES2_FOUND        - system has OpenGLES
-#  OPENGLES2_INCLUDE_DIR  - the GL include directory
-#  OPENGLES2_LIBRARIES    - Link these to use OpenGLES
-#
-#  EGL_FOUND        - system has EGL
-#  EGL_INCLUDE_DIR  - the EGL include directory
-#  EGL_LIBRARIES    - Link these to use EGL
-
-# Win32 and Apple are not tested!
-# Linux tested and works
-
-if(WIN32)
-	find_path(OPENGLES2_INCLUDE_DIR GLES2/gl2.h)
-	find_library(OPENGLES2_LIBRARY libGLESv2)
-elseif(APPLE)
-	create_search_paths(/Developer/Platforms)
-	findpkg_framework(OpenGLES2)
-	set(OPENGLES2_LIBRARY "-framework OpenGLES")
-else()
-	# Unix
-	find_path(OPENGLES2_INCLUDE_DIR GLES2/gl2.h
-		PATHS /usr/openwin/share/include
-			/opt/graphics/OpenGL/include
-			/usr/X11R6/include
-			/usr/include
-	)
-
-	find_library(OPENGLES2_LIBRARY
-		NAMES GLESv2
-		PATHS /opt/graphics/OpenGL/lib
-			/usr/openwin/lib
-			/usr/X11R6/lib
-			/usr/lib
-	)
-
-	include(FindPackageHandleStandardArgs)
-	find_package_handle_standard_args(OpenGLES2 DEFAULT_MSG OPENGLES2_LIBRARY OPENGLES2_INCLUDE_DIR)
-
-	find_path(EGL_INCLUDE_DIR EGL/egl.h
-		PATHS /usr/openwin/share/include
-			/opt/graphics/OpenGL/include
-			/usr/X11R6/include
-			/usr/include
-	)
-
-	find_library(EGL_LIBRARY
-		NAMES EGL
-		PATHS /opt/graphics/OpenGL/lib
-			/usr/openwin/lib
-			/usr/X11R6/lib
-			/usr/lib
-	)
-
-	find_package_handle_standard_args(EGL DEFAULT_MSG EGL_LIBRARY EGL_INCLUDE_DIR)
-endif()
-
-set(OPENGLES2_LIBRARIES ${OPENGLES2_LIBRARY})
-set(EGL_LIBRARIES ${EGL_LIBRARY})
-
-mark_as_advanced(
-	OPENGLES2_INCLUDE_DIR
-	OPENGLES2_LIBRARY
-	EGL_INCLUDE_DIR
-	EGL_LIBRARY
-)

src/CMakeLists.txt

@@ -98,8 +98,8 @@ if(BUILD_CLIENT AND ENABLE_SOUND)
 	endif()
 endif()
 
-
+# TODO: this should be removed one day, we can enable it unconditionally
-option(ENABLE_GLES "Use OpenGL ES instead of OpenGL" FALSE)
+option(ENABLE_GLES "Enable extra support code for OpenGL ES" FALSE)
 mark_as_advanced(ENABLE_GLES)
 
 option(ENABLE_TOUCH "Enable Touchscreen support" FALSE)
@@ -107,21 +107,6 @@ if(ENABLE_TOUCH)
 	add_definitions(-DHAVE_TOUCHSCREENGUI)
 endif()
 
-if(BUILD_CLIENT)
-	# transitive dependency from Irrlicht (see longer explanation below)
-	if(NOT WIN32)
-		if(ENABLE_GLES)
-			find_package(OpenGLES2 REQUIRED)
-		else()
-			set(OPENGL_GL_PREFERENCE "LEGACY" CACHE STRING
-				"See CMake Policy CMP0072 for reference. GLVND is broken on some nvidia setups")
-			set(OpenGL_GL_PREFERENCE ${OPENGL_GL_PREFERENCE})
-
-			find_package(OpenGL REQUIRED)
-		endif()
-	endif()
-endif()
-
 if(BUILD_CLIENT)
 	find_package(Freetype REQUIRED)
 endif()
@@ -544,18 +529,6 @@ if(BUILD_CLIENT)
 		)
 	endif()
 
-	if(ENABLE_GLES)
-		target_link_libraries(
-			${PROJECT_NAME}
-			${OPENGLES2_LIBRARIES}
-			${EGL_LIBRARIES}
-		)
-	else()
-		target_link_libraries(
-			${PROJECT_NAME}
-			${OPENGL_LIBRARIES}
-		)
-	endif()
 	if(USE_GETTEXT)
 		target_link_libraries(
 			${PROJECT_NAME}