Platform: disallow WindowFlag::Contextless when creating a GL context.

Used to be silently ignored in some places, silently discarded in some
other and probably causing an error elsewhere. Better be strict instead.

src/Magnum/Platform/EmscriptenApplication.cpp

@@ -343,7 +343,10 @@ bool EmscriptenApplication::tryCreate(const Configuration& configuration) {
 
 #ifdef MAGNUM_TARGET_GL
 bool EmscriptenApplication::tryCreate(const Configuration& configuration, const GLConfiguration& glConfiguration) {
-    CORRADE_ASSERT(_context->version() == GL::Version::None, "Platform::EmscriptenApplication::tryCreate(): window with OpenGL context already created", false);
+    CORRADE_ASSERT(!(configuration.windowFlags() & Configuration::WindowFlag::Contextless),
+        "Platform::EmscriptenApplication::tryCreate(): cannot pass Configuration::WindowFlag::Contextless when creating an OpenGL context", false);
+    CORRADE_ASSERT(_context->version() == GL::Version::None,
+        "Platform::EmscriptenApplication::tryCreate(): window with OpenGL context already created", false);
 
     /* Create emscripten WebGL context */
     EmscriptenWebGLContextAttributes attrs;

src/Magnum/Platform/EmscriptenApplication.h

@@ -1216,7 +1216,10 @@ class EmscriptenApplication::Configuration {
              * @ref EmscriptenApplication(const Arguments&, const Configuration&),
              * @ref create(const Configuration&) or
              * @ref tryCreate(const Configuration&) to prevent implicit
-             * creation of an WebGL context.
+             * creation of an WebGL context. Can't be used with
+             * @ref EmscriptenApplication(const Arguments&, const Configuration&, const GLConfiguration&),
+             * @ref create(const Configuration&, const GLConfiguration&) or
+             * @ref tryCreate(const Configuration&, const GLConfiguration&).
              */
             Contextless = 1 << 0,
 

src/Magnum/Platform/GlfwApplication.cpp

@@ -409,7 +409,10 @@ GlfwApplication::InputEvent::Modifiers currentGlfwModifiers(GLFWwindow* window)
 
 #ifdef MAGNUM_TARGET_GL
 bool GlfwApplication::tryCreate(const Configuration& configuration, const GLConfiguration& glConfiguration) {
-    CORRADE_ASSERT(!_window && _context->version() == GL::Version::None, "Platform::GlfwApplication::tryCreate(): window with OpenGL context already created", false);
+    CORRADE_ASSERT(!(configuration.windowFlags() & Configuration::WindowFlag::Contextless),
+        "Platform::GlfwApplication::tryCreate(): cannot pass Configuration::WindowFlag::Contextless when creating an OpenGL context", false);
+    CORRADE_ASSERT(!_window && _context->version() == GL::Version::None,
+        "Platform::GlfwApplication::tryCreate(): window with OpenGL context already created", false);
 
     /* Save DPI scaling values from configuration for future use, scale window
        based on those */

src/Magnum/Platform/GlfwApplication.h

@@ -1113,7 +1113,10 @@ class GlfwApplication::Configuration {
              * @ref GlfwApplication(const Arguments&, const Configuration&),
              * @ref create(const Configuration&) or
              * @ref tryCreate(const Configuration&) to prevent implicit
-             * creation of an OpenGL context.
+             * creation of an OpenGL context. Can't be used with
+             * @ref GlfwApplication(const Arguments&, const Configuration&, const GLConfiguration&),
+             * @ref create(const Configuration&, const GLConfiguration&) or
+             * @ref tryCreate(const Configuration&, const GLConfiguration&).
              *
              * @note Supported since GLFW 3.2.
              */

src/Magnum/Platform/Sdl2Application.cpp

@@ -470,7 +470,10 @@ bool Sdl2Application::tryCreate(const Configuration& configuration) {
 
 #ifdef MAGNUM_TARGET_GL
 bool Sdl2Application::tryCreate(const Configuration& configuration, const GLConfiguration& glConfiguration) {
-    CORRADE_ASSERT(_context->version() == GL::Version::None, "Platform::Sdl2Application::tryCreate(): context already created", false);
+    CORRADE_ASSERT(!(configuration.windowFlags() & Configuration::WindowFlag::Contextless),
+        "Platform::Sdl2Application::tryCreate(): cannot pass Configuration::WindowFlag::Contextless when creating an OpenGL context", false);
+    CORRADE_ASSERT(_context->version() == GL::Version::None,
+        "Platform::Sdl2Application::tryCreate(): context already created", false);
 
     /* Enable double buffering, set up buffer sizes */
     SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
@@ -621,7 +624,7 @@ bool Sdl2Application::tryCreate(const Configuration& configuration, const GLConf
         if(!(_window = SDL_CreateWindow(configuration.title().data(),
             SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
             scaledWindowSize.x(), scaledWindowSize.y(),
-            SDL_WINDOW_OPENGL|SDL_WINDOW_HIDDEN|SDL_WINDOW_ALLOW_HIGHDPI|Uint32(configuration.windowFlags()&~Configuration::WindowFlag::Contextless))))
+            SDL_WINDOW_OPENGL|SDL_WINDOW_HIDDEN|SDL_WINDOW_ALLOW_HIGHDPI|Uint32(configuration.windowFlags()))))
         {
             Error() << "Platform::Sdl2Application::tryCreate(): cannot create window:" << SDL_GetError();
             return false;

src/Magnum/Platform/Sdl2Application.h

@@ -1726,7 +1726,10 @@ class Sdl2Application::Configuration {
              * @ref Sdl2Application(const Arguments&, const Configuration&),
              * @ref create(const Configuration&) or
              * @ref tryCreate(const Configuration&) to prevent implicit
-             * creation of an OpenGL context.
+             * creation of an OpenGL context. Can't be used with
+             * @ref Sdl2Application(const Arguments&, const Configuration&, const GLConfiguration&),
+             * @ref create(const Configuration&, const GLConfiguration&) or
+             * @ref tryCreate(const Configuration&, const GLConfiguration&).
              */
             Contextless = 1u << 31, /* Hope this won't ever conflict with anything */