Split the OpenGL layer out, pt 29: SDL2 and GLFW apps w/o GL.

CMakeLists.txt

@@ -113,7 +113,7 @@ option(WITH_SHADERS "Build Shaders library" ON)
 cmake_dependent_option(WITH_TEXT "Build Text library" ON "NOT WITH_FONTCONVERTER;NOT WITH_MAGNUMFONT;NOT WITH_MAGNUMFONTCONVERTER" ON)
 cmake_dependent_option(WITH_TEXTURETOOLS "Build TextureTools library" ON "NOT WITH_TEXT;NOT WITH_DISTANCEFIELDCONVERTER" ON)
 cmake_dependent_option(WITH_TRADE "Build Trade library" ON "NOT WITH_MESHTOOLS;NOT WITH_PRIMITIVES;NOT WITH_IMAGECONVERTER;NOT WITH_ANYIMAGEIMPORTER;NOT WITH_ANYIMAGECONVERTER;NOT WITH_ANYSCENEIMPORTER;NOT WITH_OBJIMPORTER;NOT WITH_TGAIMAGECONVERTER;NOT WITH_TGAIMPORTER" ON)
-cmake_dependent_option(WITH_GL "Build GL library" ON "NOT WITH_SHADERS;NOT WITH_TEXT;NOT WITH_GL_INFO;NOT WITH_ANDROIDAPPLICATION;NOT WITH_WINDOWLESSIOSAPPLICATION;NOT WITH_CGLCONTEXT;NOT WITH_GLXAPPLICATION;NOT WITH_GLXCONTEXT;NOT WITH_XEGLAPPLICATION;NOT WITH_WINDOWLESSWGLAPPLICATION;NOT WITH_GLXCONTEXT;NOT WITH_XEGLAPPLICATION;NOT WITH_WINDOWLESSWGLAPPLICATION;NOT WITH_WGLCONTEXT;NOT WITH_WINDOWLESSWINDOWSEGLAPPLICATION;NOT WITH_GLFWAPPLICATION;NOT WITH_GLUTAPPLICATION;NOT WITH_SDL2APPLICATION;NOT WITH_DISTANCEFIELDCONVERTER;NOT WITH_FONTCONVERTER;NOT WITH_IMAGECONVERTER" ON)
+cmake_dependent_option(WITH_GL "Build GL library" ON "NOT WITH_SHADERS;NOT WITH_TEXT;NOT WITH_GL_INFO;NOT WITH_ANDROIDAPPLICATION;NOT WITH_WINDOWLESSIOSAPPLICATION;NOT WITH_CGLCONTEXT;NOT WITH_GLXAPPLICATION;NOT WITH_GLXCONTEXT;NOT WITH_XEGLAPPLICATION;NOT WITH_WINDOWLESSWGLAPPLICATION;NOT WITH_GLXCONTEXT;NOT WITH_XEGLAPPLICATION;NOT WITH_WINDOWLESSWGLAPPLICATION;NOT WITH_WGLCONTEXT;NOT WITH_WINDOWLESSWINDOWSEGLAPPLICATION;NOT WITH_GLUTAPPLICATION;NOT WITH_DISTANCEFIELDCONVERTER;NOT WITH_FONTCONVERTER;NOT WITH_IMAGECONVERTER" ON)
 option(WITH_PRIMITIVES "Builf Primitives library" ON)
 
 cmake_dependent_option(TARGET_GL "Build libraries with OpenGL interoperability" ON "WITH_GL" OFF)

doc/building.dox

@@ -456,7 +456,7 @@ your platform best:
     GL library.
 -   `WITH_GLFWAPPLICATION` --- Build the
     @ref Platform::GlfwApplication "GlfwApplication" library. Depends on
-    [GLFW](http://glfw.org). Enables also building of the GL library.
+    [GLFW](http://glfw.org).
 -   `WITH_GLUTAPPLICATION` --- Build the
     @ref Platform::GlutApplication "GlutApplication" library. Depends on
     [GLUT](http://freeglut.sourceforge.net/). Enables also building of the GL
@@ -466,7 +466,7 @@ your platform best:
     Enables also building of the GL library.
 -   `WITH_SDL2APPLICATION` --- Build the
     @ref Platform::Sdl2Application "Sdl2Application" library. Depends on
-    [SDL2](http://www.libsdl.org). Enables also building of the GL library.
+    [SDL2](http://www.libsdl.org).
 -   `WITH_XEGLAPPLICATION` --- Build the
     @ref Platform::XEglApplication "XEglApplication" library. Enables also
     building of the GL library.

doc/changelog.dox

@@ -101,6 +101,10 @@ See also:
 
 @subsubsection changelog-latest-new-platform Platform libraries
 
+-   Ability to create @ref Platform::Sdl2Application and
+    @ref Platform::GlfwApplication classes without implicitly created OpenGL
+    context by passing @ref Platform::Sdl2Application::Configuration::WindowFlag::Contextless "Configuration::WindowFlag::Contextless"
+    to them. These two can be now also built completely without the GL library.
 -   Added @ref Platform::AndroidApplication::windowSize()
 -   Added @ref Platform::AndroidApplication::nativeActivity() to access
     underlying `ANativeActivity` structure for calling various Android APIs

modules/FindMagnum.cmake

@@ -395,10 +395,20 @@ endif()
 
 set(_MAGNUM_Trade_DEPENDENCIES )
 set(_MAGNUM_AndroidApplication_DEPENDENCIES GL)
-set(_MAGNUM_GlfwApplication_DEPENDENCIES GL)
+
+set(_MAGNUM_GlfwApplication_DEPENDENCIES )
+if(MAGNUM_TARGET_GL)
+    list(APPEND _MAGNUM_GlfwApplication_DEPENDENCIES GL)
+endif()
+
 set(_MAGNUM_GlutApplication_DEPENDENCIES GL)
 set(_MAGNUM_GlxApplication_DEPENDENCIES GL)
-set(_MAGNUM_Sdl2Application_DEPENDENCIES GL)
+
+set(_MAGNUM_Sdl2Application_DEPENDENCIES )
+if(MAGNUM_TARGET_GL)
+    list(APPEND _MAGNUM_Sdl2Application_DEPENDENCIES GL)
+endif()
+
 set(_MAGNUM_WindowlessCglApplication_DEPENDENCIES GL)
 set(_MAGNUM_WindowlessEglApplication_DEPENDENCIES GL)
 set(_MAGNUM_WindowlessGlxApplication_DEPENDENCIES GL)

src/Magnum/Platform/CMakeLists.txt

@@ -41,7 +41,7 @@ set(MagnumPlatform_FILES )
 install(FILES ${MagnumPlatform_HEADERS} DESTINATION ${MAGNUM_INCLUDE_INSTALL_DIR}/Platform)
 
 # Decide about platform-specific context for cross-platform toolkits
-if(WITH_GLFWAPPLICATION OR WITH_GLUTAPPLICATION OR WITH_SDL2APPLICATION)
+if((WITH_GLFWAPPLICATION OR WITH_GLUTAPPLICATION OR WITH_SDL2APPLICATION) AND TARGET_GL)
     if(CORRADE_TARGET_APPLE AND NOT MAGNUM_TARGET_GLES)
         set(NEED_CGLCONTEXT 1)
         set(MagnumSomeContext_OBJECTS $<TARGET_OBJECTS:MagnumCglContextObjects>)
@@ -111,10 +111,11 @@ if(WITH_GLFWAPPLICATION)
         message(FATAL_ERROR "GLFW library, required by GlfwApplication, was not found. Set WITH_GLFWAPPLICATION to OFF to skip building it.")
     endif()
 
-    set(MagnumGlfwApplication_SRCS
+    set(MagnumGlfwApplication_SRCS GlfwApplication.cpp)
-        GlfwApplication.cpp
-        ${MagnumSomeContext_OBJECTS})
     set(MagnumGlfwApplication_HEADERS GlfwApplication.h)
+    if(TARGET_GL)
+        list(APPEND MagnumGlfwApplication_SRCS ${MagnumSomeContext_OBJECTS})
+    endif()
 
     add_library(MagnumGlfwApplication STATIC
         ${MagnumGlfwApplication_SRCS}
@@ -124,7 +125,10 @@ if(WITH_GLFWAPPLICATION)
         FOLDER "Magnum/Platform")
     # Assuming that PIC is not needed because the Application lib is always
     # linked to the executable and not to any intermediate shared lib
-    target_link_libraries(MagnumGlfwApplication PUBLIC MagnumGL GLFW::GLFW)
+    target_link_libraries(MagnumGlfwApplication PUBLIC Magnum GLFW::GLFW)
+    if(TARGET_GL)
+        target_link_libraries(MagnumGlfwApplication PUBLIC MagnumGL)
+    endif()
 
     install(FILES ${MagnumGlfwApplication_HEADERS} DESTINATION ${MAGNUM_INCLUDE_INSTALL_DIR}/Platform)
     install(TARGETS MagnumGlfwApplication
@@ -176,10 +180,11 @@ if(WITH_SDL2APPLICATION)
         message(FATAL_ERROR "SDL2 library, required by Sdl2Application, was not found. Set WITH_SDL2APPLICATION to OFF to skip building it.")
     endif()
 
-    set(MagnumSdl2Application_SRCS
+    set(MagnumSdl2Application_SRCS Sdl2Application.cpp)
-        Sdl2Application.cpp
-        ${MagnumSomeContext_OBJECTS})
     set(MagnumSdl2Application_HEADERS Sdl2Application.h)
+    if(TARGET_GL)
+        list(APPEND MagnumSdl2Application_SRCS ${MagnumSomeContext_OBJECTS})
+    endif()
 
     add_library(MagnumSdl2Application STATIC
         ${MagnumSdl2Application_SRCS}
@@ -189,7 +194,10 @@ if(WITH_SDL2APPLICATION)
         FOLDER "Magnum/Platform")
     # Assuming that PIC is not needed because the Application lib is always
     # linked to the executable and not to any intermediate shared lib
-    target_link_libraries(MagnumSdl2Application PUBLIC MagnumGL SDL2::SDL2)
+    target_link_libraries(MagnumSdl2Application PUBLIC Magnum SDL2::SDL2)
+    if(TARGET_GL)
+        target_link_libraries(MagnumSdl2Application PUBLIC MagnumGL)
+    endif()
 
     install(FILES ${MagnumSdl2Application_HEADERS} DESTINATION ${MAGNUM_INCLUDE_INSTALL_DIR}/Platform)
     install(TARGETS MagnumSdl2Application

src/Magnum/Platform/GlfwApplication.cpp

@@ -30,9 +30,12 @@
 #include <Corrade/Utility/String.h>
 #include <Corrade/Utility/Unicode.h>
 
+#include "Magnum/Platform/ScreenedApplication.hpp"
+
+#ifdef MAGNUM_TARGET_GL
 #include "Magnum/GL/Version.h"
 #include "Magnum/Platform/GLContext.h"
-#include "Magnum/Platform/ScreenedApplication.hpp"
+#endif
 
 namespace Magnum { namespace Platform {
 
@@ -49,13 +52,17 @@ GlfwApplication::GlfwApplication(const Arguments& arguments, const Configuration
     create(configuration);
 }
 
+#ifdef MAGNUM_TARGET_GL
 GlfwApplication::GlfwApplication(const Arguments& arguments, const Configuration& configuration, const GLConfiguration& glConfiguration): GlfwApplication{arguments, NoCreate} {
     create(configuration, glConfiguration);
 }
+#endif
 
 GlfwApplication::GlfwApplication(const Arguments& arguments, NoCreateT):
-    _context{new GLContext{NoCreate, arguments.argc, arguments.argv}},
     _flags{Flag::Redraw}
+    #ifdef MAGNUM_TARGET_GL
+    , _context{new GLContext{NoCreate, arguments.argc, arguments.argv}}
+    #endif
 {
     /* Save global instance */
     _instance = this;
@@ -67,6 +74,10 @@ GlfwApplication::GlfwApplication(const Arguments& arguments, NoCreateT):
         Error() << "Could not initialize GLFW";
         std::exit(8);
     }
+
+    #ifndef MAGNUM_TARGET_GL
+    static_cast<void>(arguments);
+    #endif
 }
 
 void GlfwApplication::create() {
@@ -77,14 +88,71 @@ void GlfwApplication::create(const Configuration& configuration) {
     if(!tryCreate(configuration)) std::exit(1);
 }
 
+#ifdef MAGNUM_TARGET_GL
 void GlfwApplication::create(const Configuration& configuration, const GLConfiguration& glConfiguration) {
     if(!tryCreate(configuration, glConfiguration)) std::exit(1);
 }
+#endif
 
 bool GlfwApplication::tryCreate(const Configuration& configuration) {
-    return tryCreate(configuration, GLConfiguration{});
+    #ifdef MAGNUM_TARGET_GL
+    #ifdef GLFW_NO_API
+    if(!(configuration.windowFlags() & Configuration::WindowFlag::Contextless))
+    #endif
+    {
+        return tryCreate(configuration, GLConfiguration{});
+    }
+    #endif
+
+    CORRADE_ASSERT(!_window, "Platform::GlfwApplication::tryCreate(): window already created", false);
+
+    /* Window flags */
+    GLFWmonitor* monitor = nullptr; /* Needed for setting fullscreen */
+    if (configuration.windowFlags() >= Configuration::WindowFlag::Fullscreen) {
+        monitor = glfwGetPrimaryMonitor();
+        glfwWindowHint(GLFW_AUTO_ICONIFY, configuration.windowFlags() >= Configuration::WindowFlag::AutoIconify);
+    } else {
+        const Configuration::WindowFlags& flags = configuration.windowFlags();
+        glfwWindowHint(GLFW_RESIZABLE, flags >= Configuration::WindowFlag::Resizable);
+        glfwWindowHint(GLFW_VISIBLE, !(flags >= Configuration::WindowFlag::Hidden));
+        #ifdef GLFW_MAXIMIZED
+        glfwWindowHint(GLFW_MAXIMIZED, flags >= Configuration::WindowFlag::Maximized);
+        #endif
+        glfwWindowHint(GLFW_FLOATING, flags >= Configuration::WindowFlag::Floating);
+    }
+    glfwWindowHint(GLFW_FOCUSED, configuration.windowFlags() >= Configuration::WindowFlag::Focused);
+
+    #ifdef GLFW_NO_API
+    /* Disable implicit GL context c/reation */
+    glfwWindowHint(GLFW_CONTEXT_CREATION_API, GLFW_NO_API);
+    #endif
+
+    /* Create the window */
+    _window = glfwCreateWindow(configuration.size().x(), configuration.size().y(), configuration.title().c_str(), monitor, nullptr);
+    if(!_window) {
+        Error() << "Platform::GlfwApplication::tryCreate(): cannot create window";
+        glfwTerminate();
+        return false;
+    }
+
+    /* Proceed with configuring other stuff that couldn't be done with window
+       hints */
+    if(configuration.windowFlags() >= Configuration::WindowFlag::Minimized)
+        glfwIconifyWindow(_window);
+    glfwSetInputMode(_window, GLFW_CURSOR, Int(configuration.cursorMode()));
+
+    /* Set callbacks */
+    glfwSetFramebufferSizeCallback(_window, staticViewportEvent);
+    glfwSetKeyCallback(_window, staticKeyEvent);
+    glfwSetCursorPosCallback(_window, staticMouseMoveEvent);
+    glfwSetMouseButtonCallback(_window, staticMouseEvent);
+    glfwSetScrollCallback(_window, staticMouseScrollEvent);
+    glfwSetCharCallback(_window, staticTextInputEvent);
+
+    return true;
 }
 
+#ifdef MAGNUM_TARGET_GL
 bool GlfwApplication::tryCreate(const Configuration& configuration, const GLConfiguration&
     #ifndef MAGNUM_BUILD_DEPRECATED
     glConfiguration
@@ -178,6 +246,7 @@ bool GlfwApplication::tryCreate(const Configuration& configuration, const GLConf
     /* Return true if the initialization succeeds */
     return _context->tryCreate();
 }
+#endif
 
 GlfwApplication::~GlfwApplication() {
     glfwDestroyWindow(_window);
@@ -292,12 +361,18 @@ void GlfwApplication::mouseMoveEvent(MouseMoveEvent&) {}
 void GlfwApplication::mouseScrollEvent(MouseScrollEvent&) {}
 void GlfwApplication::textInputEvent(TextInputEvent&) {}
 
+#ifdef MAGNUM_TARGET_GL
+GlfwApplication::GLConfiguration::GLConfiguration(): _sampleCount{0}, _version{GL::Version::None} {}
+
+GlfwApplication::GLConfiguration::~GLConfiguration() = default;
+#endif
+
 GlfwApplication::Configuration::Configuration():
     _title{"Magnum GLFW Application"},
     _size{800, 600},
     _windowFlags{WindowFlag::Focused},
     _cursorMode{CursorMode::Normal}
-    #ifdef MAGNUM_BUILD_DEPRECATED
+    #if defined(MAGNUM_BUILD_DEPRECATED) && defined(MAGNUM_TARGET_GL)
     , _sampleCount{0}, _version{GL::Version::None}
     #endif
     {}

src/Magnum/Platform/GlfwApplication.h

@@ -36,12 +36,14 @@
 
 #include "Magnum/Magnum.h"
 #include "Magnum/Tags.h"
-#include "Magnum/GL/GL.h"
 #include "Magnum/Math/Vector2.h"
 #include "Magnum/Platform/Platform.h"
 
+#ifdef MAGNUM_TARGET_GL
+#include "Magnum/GL/GL.h"
 /* We must include our own GL headers first to avoid conflicts */
 #include "Magnum/GL/OpenGL.h"
+#endif
 
 #include <GLFW/glfw3.h>
 
@@ -123,7 +125,9 @@ class GlfwApplication {
         };
 
         class Configuration;
+        #ifdef MAGNUM_TARGET_GL
         class GLConfiguration;
+        #endif
         class InputEvent;
         class KeyEvent;
         class MouseEvent;
@@ -131,6 +135,7 @@ class GlfwApplication {
         class MouseScrollEvent;
         class TextInputEvent;
 
+        #ifdef MAGNUM_TARGET_GL
         /**
          * @brief Construct with given configuration for OpenGL context
          * @param arguments         Application arguments
@@ -141,13 +146,23 @@ class GlfwApplication {
          * See @ref Configuration for more information. The program exits if
          * the context cannot be created, see @ref tryCreate() for an
          * alternative.
+         *
+         * @note This function is available only if Magnum is compiled with
+         *      @ref MAGNUM_TARGET_GL enabled (done by default). See
+         *      @ref building-features for more information.
          */
         explicit GlfwApplication(const Arguments& arguments, const Configuration& configuration, const GLConfiguration& glConfiguration);
+        #endif
 
         /**
-         * @brief Construct with given configuration and OpenGL context
+         * @brief Construct with given configuration
+         *
+         * If @ref Configuration::WindowFlag::Contextless is present or Magnum
+         * was not built with @ref MAGNUM_TARGET_GL, this creates a window
+         * without any GPU context attached, leaving that part on the user.
          *
-         * Equivalent to calling
+         * If none of the flags is present and Magnum was built with
+         * @ref MAGNUM_TARGET_GL, this is equivalent to calling
          * @ref GlfwApplication(const Arguments&, const Configuration&, const GLConfiguration&)
          * with default-constructed @ref GLConfiguration.
          *
@@ -217,6 +232,7 @@ class GlfwApplication {
            faster than public pure virtual destructor */
         ~GlfwApplication();
 
+        #ifdef MAGNUM_TARGET_GL
         /**
          * @brief Create a window with given configuration for OpenGL context
          * @param configuration     Application configuration
@@ -226,13 +242,23 @@ class GlfwApplication {
          * itself, i.e. when passing @ref NoCreate to it. Error message is
          * printed and the program exits if the context cannot be created, see
          * @ref tryCreate() for an alternative.
+         *
+         * @note This function is available only if Magnum is compiled with
+         *      @ref MAGNUM_TARGET_GL enabled (done by default). See
+         *      @ref building-features for more information.
          */
         void create(const Configuration& configuration, const GLConfiguration& glConfiguration);
+        #endif
 
         /**
          * @brief Create a window with given configuration
          *
-         * Equivalent to calling
+         * If @ref Configuration::WindowFlag::Contextless is present or Magnum
+         * was not built with @ref MAGNUM_TARGET_GL, this creates a window
+         * without any GPU context attached, leaving that part on the user.
+         *
+         * If none of the flags is present and Magnum was built with
+         * @ref MAGNUM_TARGET_GL, this is equivalent to calling
          * @ref create(const Configuration&, const GLConfiguration&) with
          * default-constructed @ref GLConfiguration.
          *
@@ -264,14 +290,20 @@ class GlfwApplication {
         }
         #endif
 
+        #ifdef MAGNUM_TARGET_GL
         /**
          * @brief Try to create context with given configuration for OpenGL context
          *
          * Unlike @ref create(const Configuration&, const GLConfiguration&)
          * returns @cpp false @ce if the context cannot be created,
          * @cpp true @ce otherwise.
+         *
+         * @note This function is available only if Magnum is compiled with
+         *      @ref MAGNUM_TARGET_GL enabled (done by default). See
+         *      @ref building-features for more information.
          */
         bool tryCreate(const Configuration& configuration, const GLConfiguration& glConfiguration);
+        #endif
 
         /**
          * @brief Try to create context with given configuration
@@ -448,12 +480,15 @@ class GlfwApplication {
         static GlfwApplication* _instance;
 
         GLFWwindow* _window;
-        std::unique_ptr<Platform::GLContext> _context;
         Flags _flags;
+        #ifdef MAGNUM_TARGET_GL
+        std::unique_ptr<Platform::GLContext> _context;
+        #endif
 };
 
 CORRADE_ENUMSET_OPERATORS(GlfwApplication::Flags)
 
+#ifdef MAGNUM_TARGET_GL
 /**
 @brief OpenGL context configuration
 
@@ -561,6 +596,7 @@ class GlfwApplication::GLConfiguration {
 };
 
 CORRADE_ENUMSET_OPERATORS(GlfwApplication::GLConfiguration::Flags)
+#endif
 
 /**
 @brief Configuration
@@ -570,7 +606,7 @@ Double-buffered RGBA window with depth and stencil buffers.
 */
 class GlfwApplication::Configuration {
     public:
-        #ifdef MAGNUM_BUILD_DEPRECATED
+        #if defined(MAGNUM_BUILD_DEPRECATED) && defined(MAGNUM_TARGET_GL)
         /** @brief @copybrief GLConfiguration::Flag
          * @deprecated Use @ref GLConfiguration::Flag instead.
          */
@@ -618,7 +654,21 @@ class GlfwApplication::Configuration {
              */
             AutoIconify = 1 << 6,
 
-            Focused = 1 << 7       /**< Window has input focus */
+            Focused = 1 << 7,      /**< Window has input focus */
+
+            #if defined(DOXYGEN_GENERATING_OUTPUT) || defined(GLFW_NO_API)
+            /**
+             * Do not create any GPU context. Use together with
+             * @ref GlfwApplication(const Arguments&),
+             * @ref GlfwApplication(const Arguments&, const Configuration&),
+             * @ref create(const Configuration&) or
+             * @ref tryCreate(const Configuration&) to prevent implicit
+             * creation of an OpenGL context.
+             *
+             * @note Supported since GLFW 3.2.
+             */
+            Contextless = 1 << 8
+            #endif
         };
 
         /**
@@ -703,7 +753,7 @@ class GlfwApplication::Configuration {
             return *this;
         }
 
-        #ifdef MAGNUM_BUILD_DEPRECATED
+        #if defined(MAGNUM_BUILD_DEPRECATED) && defined(MAGNUM_TARGET_GL)
         /** @brief @copybrief GLConfiguration::flags()
          * @deprecated Use @ref GLConfiguration::flags() instead.
          */
@@ -764,7 +814,7 @@ class GlfwApplication::Configuration {
         Vector2i _size;
         WindowFlags _windowFlags;
         CursorMode _cursorMode;
-        #ifdef MAGNUM_BUILD_DEPRECATED
+        #if defined(MAGNUM_BUILD_DEPRECATED) && defined(MAGNUM_TARGET_GL)
         Int _sampleCount;
         GL::Version _version;
         Flags _flags;

src/Magnum/Platform/ScreenedApplication.h

@@ -98,18 +98,27 @@ The following specialization are explicitly compiled into each particular
 */
 template<class Application> class BasicScreenedApplication: public Application, private Containers::LinkedList<BasicScreen<Application>> {
     public:
+        #ifdef MAGNUM_TARGET_GL
         /**
-         * @brief Default constructor
+         * @brief Construct with given configuration for OpenGL context
-         * @param arguments         Application arguments
+         *
-         * @param configuration     Application configuration
+         * Passes the arguments through to a particular application
-         * @param glConfiguration   OpenGL context configuration
+         * constructor.
+         *
+         * @note This function is available only if Magnum is compiled with
+         *      @ref MAGNUM_TARGET_GL enabled (done by default). See
+         *      @ref building-features for more information.
+         */
+        explicit BasicScreenedApplication(const typename Application::Arguments& arguments, const typename Application::Configuration& configuration, const typename Application::GLConfiguration& glConfiguration);
+        #endif
+
+        /**
+         * @brief Construct with given configuration
          *
-         * Creates application with default or user-specified configuration.
+         * Passes the arguments through to a particular application
-         * See @ref Sdl2Application::Configuration "Configuration" for more
+         * constructor.
-         * information. The program exits if the context cannot be created, see
-         * below for an alternative.
          */
-        explicit BasicScreenedApplication(const typename Application::Arguments& arguments, const typename Application::Configuration& configuration = typename Application::Configuration{}, const typename Application::GLConfiguration& glConfiguration = typename Application::GLConfiguration{});
+        explicit BasicScreenedApplication(const typename Application::Arguments& arguments, const typename Application::Configuration& configuration = typename Application::Configuration{});
 
         /**
          * @brief Constructor

src/Magnum/Platform/ScreenedApplication.hpp

@@ -43,7 +43,11 @@ template<class Application> void BasicScreen<Application>::mousePressEvent(Mouse
 template<class Application> void BasicScreen<Application>::mouseReleaseEvent(MouseEvent&) {}
 template<class Application> void BasicScreen<Application>::mouseMoveEvent(MouseMoveEvent&) {}
 
+#ifdef MAGNUM_TARGET_GL
 template<class Application> BasicScreenedApplication<Application>::BasicScreenedApplication(const typename Application::Arguments& arguments, const typename Application::Configuration& configuration, const typename Application::GLConfiguration& glConfiguration): Application(arguments, configuration, glConfiguration) {}
+#endif
+
+template<class Application> BasicScreenedApplication<Application>::BasicScreenedApplication(const typename Application::Arguments& arguments, const typename Application::Configuration& configuration): Application(arguments, configuration) {}
 
 template<class Application> BasicScreenedApplication<Application>::BasicScreenedApplication(const typename Application::Arguments& arguments, NoCreateT): Application(arguments, NoCreate) {}
 

src/Magnum/Platform/Sdl2Application.cpp

@@ -32,11 +32,14 @@
 #include <emscripten/emscripten.h>
 #endif
 
-#include "Magnum/GL/Version.h"
 #include "Magnum/Math/Range.h"
-#include "Magnum/Platform/GLContext.h"
 #include "Magnum/Platform/ScreenedApplication.hpp"
 
+#ifdef MAGNUM_TARGET_GL
+#include "Magnum/GL/Version.h"
+#include "Magnum/Platform/GLContext.h"
+#endif
+
 namespace Magnum { namespace Platform {
 
 namespace {
@@ -58,26 +61,35 @@ Sdl2Application::InputEvent::Modifiers fixedModifiers(Uint16 mod) {
 
 }
 
-Sdl2Application::Sdl2Application(const Arguments& arguments): Sdl2Application{arguments, Configuration{}, GLConfiguration{}} {}
+Sdl2Application::Sdl2Application(const Arguments& arguments): Sdl2Application{arguments, Configuration{}} {}
 
 Sdl2Application::Sdl2Application(const Arguments& arguments, const Configuration& configuration): Sdl2Application{arguments, NoCreate} {
     create(configuration);
 }
 
+#ifdef MAGNUM_TARGET_GL
 Sdl2Application::Sdl2Application(const Arguments& arguments, const Configuration& configuration, const GLConfiguration& glConfiguration): Sdl2Application{arguments, NoCreate} {
     create(configuration, glConfiguration);
 }
+#endif
 
-Sdl2Application::Sdl2Application(const Arguments& arguments, NoCreateT): _glContext{nullptr},
+Sdl2Application::Sdl2Application(const Arguments& arguments, NoCreateT):
     #ifndef CORRADE_TARGET_EMSCRIPTEN
     _minimalLoopPeriod{0},
     #endif
-    _context{new GLContext{NoCreate, arguments.argc, arguments.argv}}, _flags{Flag::Redraw}
+    #ifdef MAGNUM_TARGET_GL
+    _glContext{nullptr}, _context{new GLContext{NoCreate, arguments.argc, arguments.argv}},
+    #endif
+    _flags{Flag::Redraw}
 {
     if(SDL_Init(SDL_INIT_VIDEO) < 0) {
         Error() << "Cannot initialize SDL.";
         std::exit(1);
     }
+
+    #ifndef MAGNUM_TARGET_GL
+    static_cast<void>(arguments);
+    #endif
 }
 
 void Sdl2Application::create() {
@@ -88,14 +100,45 @@ void Sdl2Application::create(const Configuration& configuration) {
     if(!tryCreate(configuration)) std::exit(1);
 }
 
+#ifdef MAGNUM_TARGET_GL
 void Sdl2Application::create(const Configuration& configuration, const GLConfiguration& glConfiguration) {
     if(!tryCreate(configuration, glConfiguration)) std::exit(1);
 }
+#endif
 
 bool Sdl2Application::tryCreate(const Configuration& configuration) {
-    return tryCreate(configuration, GLConfiguration{});
+    #ifdef MAGNUM_TARGET_GL
+    if(!(configuration.windowFlags() & Configuration::WindowFlag::Contextless))
+        return tryCreate(configuration, GLConfiguration{});
+    #endif
+
+    #ifndef CORRADE_TARGET_EMSCRIPTEN
+    /* Create window */
+    if(!(_window = SDL_CreateWindow(
+        #ifndef CORRADE_TARGET_IOS
+        configuration.title().data(),
+        #else
+        nullptr,
+        #endif
+        SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
+        configuration.size().x(), configuration.size().y(),
+        Uint32(configuration.windowFlags()&~Configuration::WindowFlag::Contextless))))
+    {
+        Error() << "Platform::Sdl2Application::tryCreate(): cannot create window:" << SDL_GetError();
+        return false;
+    }
+    #else
+    /* Emscripten-specific initialization */
+    if(!(_glContext = SDL_SetVideoMode(configuration.size().x(), configuration.size().y(), 24, SDL_OPENGL|SDL_HWSURFACE|SDL_DOUBLEBUF))) {
+        Error() << "Platform::Sdl2Application::tryCreate(): cannot create window:" << SDL_GetError();
+        return false;
+    }
+    #endif
+
+    return true;
 }
 
+#ifdef MAGNUM_TARGET_GL
 bool Sdl2Application::tryCreate(const Configuration& configuration, const GLConfiguration&
     #ifndef MAGNUM_BUILD_DEPRECATED
     glConfiguration
@@ -246,7 +289,7 @@ bool Sdl2Application::tryCreate(const Configuration& configuration, const GLConf
         if(!(_window = SDL_CreateWindow(configuration.title().data(),
             SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
             configuration.size().x(), configuration.size().y(),
-            SDL_WINDOW_OPENGL|SDL_WINDOW_HIDDEN|Uint32(configuration.windowFlags()))))
+            SDL_WINDOW_OPENGL|SDL_WINDOW_HIDDEN|Uint32(configuration.windowFlags()&~Configuration::WindowFlag::Contextless))))
         {
             Error() << "Platform::Sdl2Application::tryCreate(): cannot create window:" << SDL_GetError();
             return false;
@@ -303,6 +346,7 @@ bool Sdl2Application::tryCreate(const Configuration& configuration, const GLConf
     /* Return true if the initialization succeeds */
     return true;
 }
+#endif
 
 Vector2i Sdl2Application::windowSize() {
     #ifndef CORRADE_TARGET_EMSCRIPTEN
@@ -344,14 +388,19 @@ bool Sdl2Application::setSwapInterval(const Int interval) {
 }
 
 Sdl2Application::~Sdl2Application() {
+    #ifdef MAGNUM_TARGET_GL
     _context.reset();
 
     #ifndef CORRADE_TARGET_EMSCRIPTEN
     SDL_GL_DeleteContext(_glContext);
-    SDL_DestroyWindow(_window);
     #else
     SDL_FreeSurface(_glContext);
     #endif
+    #endif
+
+    #ifndef CORRADE_TARGET_EMSCRIPTEN
+    SDL_DestroyWindow(_window);
+    #endif
     SDL_Quit();
 }
 
@@ -561,6 +610,7 @@ void Sdl2Application::multiGestureEvent(MultiGestureEvent&) {}
 void Sdl2Application::textInputEvent(TextInputEvent&) {}
 void Sdl2Application::textEditingEvent(TextEditingEvent&) {}
 
+#ifdef MAGNUM_TARGET_GL
 Sdl2Application::GLConfiguration::GLConfiguration():
     _sampleCount(0)
     #ifndef CORRADE_TARGET_EMSCRIPTEN
@@ -569,6 +619,7 @@ Sdl2Application::GLConfiguration::GLConfiguration():
     {}
 
 Sdl2Application::GLConfiguration::~GLConfiguration() = default;
+#endif
 
 Sdl2Application::Configuration::Configuration():
     #if !defined(CORRADE_TARGET_EMSCRIPTEN) && !defined(CORRADE_TARGET_IOS)
@@ -581,7 +632,7 @@ Sdl2Application::Configuration::Configuration():
     #else
     _size{} /* SDL2 detects someting for us */
     #endif
-    #ifdef MAGNUM_BUILD_DEPRECATED
+    #if defined(MAGNUM_BUILD_DEPRECATED) && defined(MAGNUM_TARGET_GL)
     , _sampleCount(0)
     #ifndef CORRADE_TARGET_EMSCRIPTEN
     , _version(GL::Version::None), _sRGBCapable{false}

src/Magnum/Platform/Sdl2Application.h

@@ -36,10 +36,13 @@
 
 #include "Magnum/Magnum.h"
 #include "Magnum/Tags.h"
-#include "Magnum/GL/GL.h"
 #include "Magnum/Math/Vector2.h"
 #include "Magnum/Platform/Platform.h"
 
+#ifdef MAGNUM_TARGET_GL
+#include "Magnum/GL/GL.h"
+#endif
+
 #ifdef CORRADE_TARGET_WINDOWS /* Windows version of SDL2 redefines main(), we don't want that */
 #define SDL_MAIN_HANDLED
 #endif
@@ -363,7 +366,9 @@ class Sdl2Application {
         };
 
         class Configuration;
+        #ifdef MAGNUM_TARGET_GL
         class GLConfiguration;
+        #endif
         class InputEvent;
         class KeyEvent;
         class MouseEvent;
@@ -373,6 +378,7 @@ class Sdl2Application {
         class TextInputEvent;
         class TextEditingEvent;
 
+        #ifdef MAGNUM_TARGET_GL
         /**
          * @brief Construct with given configuration for OpenGL context
          * @param arguments         Application arguments
@@ -383,14 +389,27 @@ class Sdl2Application {
          * See @ref Configuration for more information. The program exits if
          * the context cannot be created, see @ref tryCreate() for an
          * alternative.
+         *
+         * @note This function is available only if Magnum is compiled with
+         *      @ref MAGNUM_TARGET_GL enabled (done by default). See
+         *      @ref building-features for more information.
          */
         explicit Sdl2Application(const Arguments& arguments, const Configuration& configuration, const GLConfiguration& glConfiguration);
+        #endif
 
         /**
-         * @brief Construct with given configuration and default OpenGL context
+         * @brief Construct with given configuration
+         *
+         * If @ref Configuration::WindowFlag::Contextless is present or Magnum
+         * was not built with @ref MAGNUM_TARGET_GL, this creates a window
+         * without any GPU context attached, leaving that part on the user.
          *
-         * Equivalent to calling @ref Sdl2Application(const Arguments&, const Configuration&, const GLConfiguration&)
+         * If none of the flags is present and Magnum was built with
+         * @ref MAGNUM_TARGET_GL, this is equivalent to calling
+         * @ref Sdl2Application(const Arguments&, const Configuration&, const GLConfiguration&)
          * with default-constructed @ref GLConfiguration.
+         *
+         * See also @ref building-features for more information.
          */
         explicit Sdl2Application(const Arguments& arguments, const Configuration& configuration);
 
@@ -473,6 +492,7 @@ class Sdl2Application {
            faster than public pure virtual destructor */
         ~Sdl2Application();
 
+        #ifdef MAGNUM_TARGET_GL
         /**
          * @brief Create a window with given configuration for OpenGL context
          * @param configuration     Application configuration
@@ -487,14 +507,27 @@ class Sdl2Application {
          * the application first tries to create core context (OpenGL 3.2+ on
          * macOS, OpenGL 3.1+ elsewhere) and if that fails, falls back to
          * compatibility OpenGL 2.1 context.
+         *
+         * @note This function is available only if Magnum is compiled with
+         *      @ref MAGNUM_TARGET_GL enabled (done by default). See
+         *      @ref building-features for more information.
          */
         void create(const Configuration& configuration, const GLConfiguration& glConfiguration);
+        #endif
 
         /**
-         * @brief Create a window with given configuration and default OpenGL context
+         * @brief Create a window with given configuration
          *
-         * Equivalent to calling @ref create(const Configuration&, const GLConfiguration&)
+         * If @ref Configuration::WindowFlag::Contextless is present or Magnum
-         * with default-constructed @ref GLConfiguration.
+         * was not built with @ref MAGNUM_TARGET_GL, this creates a window
+         * without any GPU context attached, leaving that part on the user.
+         *
+         * If none of the flags is present and Magnum was built with
+         * @ref MAGNUM_TARGET_GL, this is equivalent to calling
+         * @ref create(const Configuration&, const GLConfiguration&) with
+         * default-constructed @ref GLConfiguration.
+         *
+         * See also @ref building-features for more information.
          */
         void create(const Configuration& configuration);
 
@@ -506,7 +539,7 @@ class Sdl2Application {
          */
         void create();
 
-        #ifdef MAGNUM_BUILD_DEPRECATED
+        #if defined(MAGNUM_BUILD_DEPRECATED) && defined(MAGNUM_TARGET_GL)
         /** @brief @copybrief create(const Configuration&, const GLConfiguration&)
          * @deprecated Use @ref create(const Configuration&, const GLConfiguration&) instead.
          */
@@ -522,13 +555,20 @@ class Sdl2Application {
         }
         #endif
 
+        #ifdef MAGNUM_TARGET_GL
         /**
          * @brief Try to create context with given configuration for OpenGL context
          *
-         * Unlike @ref create() returns @cpp false @ce if the context cannot be
+         * Unlike @ref create(const Configuration&, const GLConfiguration&)
-         * created, @cpp true @ce otherwise.
+         * returns @cpp false @ce if the context cannot be created,
+         * @cpp true @ce otherwise.
+         *
+         * @note This function is available only if Magnum is compiled with
+         *      @ref MAGNUM_TARGET_GL enabled (done by default). See
+         *      @ref building-features for more information.
          */
         bool tryCreate(const Configuration& configuration, const GLConfiguration& glConfiguration);
+        #endif
 
         /**
          * @brief Try to create context with given configuration
@@ -538,7 +578,7 @@ class Sdl2Application {
          */
         bool tryCreate(const Configuration& configuration);
 
-        #ifdef MAGNUM_BUILD_DEPRECATED
+        #if defined(MAGNUM_BUILD_DEPRECATED) && defined(MAGNUM_TARGET_GL)
         /** @brief @copybrief tryCreate(const Configuration&, const GLConfiguration&)
          * @deprecated Use @ref tryCreate(const Configuration&, const GLConfiguration&) instead.
          */
@@ -818,22 +858,32 @@ class Sdl2Application {
 
         #ifndef CORRADE_TARGET_EMSCRIPTEN
         SDL_Window* _window;
-        SDL_GLContext _glContext;
         UnsignedInt _minimalLoopPeriod;
+        #endif
+
+        #ifdef MAGNUM_TARGET_GL
+        #ifndef CORRADE_TARGET_EMSCRIPTEN
+        SDL_GLContext _glContext;
         #else
         SDL_Surface* _glContext;
         #endif
-
         std::unique_ptr<Platform::GLContext> _context;
+        #endif
 
         Flags _flags;
 };
 
+#ifdef MAGNUM_TARGET_GL
 /**
 @brief OpenGL context configuration
 
 The created window is always with double-buffered OpenGL context and 24bit
 depth buffer.
+
+@note This function is available only if Magnum is compiled with
+    @ref MAGNUM_TARGET_GL enabled (done by default). See @ref building-features
+    for more information.
+
 @see @ref Sdl2Application(), @ref create(), @ref tryCreate()
 */
 class Sdl2Application::GLConfiguration {
@@ -968,6 +1018,11 @@ class Sdl2Application::GLConfiguration {
         #endif
 };
 
+#ifndef CORRADE_TARGET_EMSCRIPTEN
+CORRADE_ENUMSET_OPERATORS(Sdl2Application::GLConfiguration::Flags)
+#endif
+#endif
+
 /**
 @brief Configuration
 
@@ -976,7 +1031,7 @@ class Sdl2Application::GLConfiguration {
 */
 class Sdl2Application::Configuration {
     public:
-        #if defined(MAGNUM_BUILD_DEPRECATED) && !defined(CORRADE_TARGET_EMSCRIPTEN)
+        #if defined(MAGNUM_BUILD_DEPRECATED) && defined(MAGNUM_TARGET_GL) && !defined(CORRADE_TARGET_EMSCRIPTEN)
         /** @brief @copybrief GLConfiguration::Flag
          * @deprecated Use @ref GLConfiguration::Flag instead.
          */
@@ -1019,7 +1074,16 @@ class Sdl2Application::Configuration {
             Hidden = SDL_WINDOW_HIDDEN,             /**< Hidden window */
             Maximized = SDL_WINDOW_MAXIMIZED,       /**< Maximized window */
             Minimized = SDL_WINDOW_MINIMIZED,       /**< Minimized window */
-            MouseLocked = SDL_WINDOW_INPUT_GRABBED  /**< Window with mouse locked */
+            MouseLocked = SDL_WINDOW_INPUT_GRABBED, /**< Window with mouse locked */
+
+            /**
+             * Do not create any GPU context. Use together with
+             * @ref Sdl2Application(const Arguments&, const Configuration&),
+             * @ref create(const Configuration&) or
+             * @ref tryCreate(const Configuration&) to prevent implicit
+             * creation of an OpenGL context.
+             */
+            Contextless = 1u << 31 /* Hope this won't ever conflict with anything */
         };
 
         /**
@@ -1099,7 +1163,7 @@ class Sdl2Application::Configuration {
             return *this;
         }
 
-        #ifdef MAGNUM_BUILD_DEPRECATED
+        #if defined(MAGNUM_BUILD_DEPRECATED) && defined(MAGNUM_TARGET_GL)
         #ifndef CORRADE_TARGET_EMSCRIPTEN
         /** @brief @copybrief GLConfiguration::flags()
          * @deprecated Use @ref GLConfiguration::flags() instead.
@@ -1167,7 +1231,7 @@ class Sdl2Application::Configuration {
         #endif
         Vector2i _size;
         WindowFlags _windowFlags;
-        #ifdef MAGNUM_BUILD_DEPRECATED
+        #if defined(MAGNUM_BUILD_DEPRECATED) && defined(MAGNUM_TARGET_GL)
         Int _sampleCount;
         #ifndef CORRADE_TARGET_EMSCRIPTEN
         GL::Version _version;
@@ -1871,9 +1935,6 @@ typedef BasicScreenedApplication<Sdl2Application> ScreenedApplication;
 #endif
 
 CORRADE_ENUMSET_OPERATORS(Sdl2Application::Flags)
-#ifndef CORRADE_TARGET_EMSCRIPTEN
-CORRADE_ENUMSET_OPERATORS(Sdl2Application::GLConfiguration::Flags)
-#endif
 CORRADE_ENUMSET_OPERATORS(Sdl2Application::Configuration::WindowFlags)
 CORRADE_ENUMSET_OPERATORS(Sdl2Application::InputEvent::Modifiers)
 CORRADE_ENUMSET_OPERATORS(Sdl2Application::MouseMoveEvent::Buttons)