Platform: add context getters to all windowless apps.

For context sharing. The windowed apps already have these.

src/Magnum/Platform/WindowlessCglApplication.h

@@ -126,6 +126,17 @@ class WindowlessCglContext {
          */
         bool makeCurrent();
 
+        /**
+         * @brief Underlying OpenGL context
+         * @m_since_latest
+         *
+         * Use in case you need to call CGL functionality directly or in order
+         * to create a shared context. Returns @cpp nullptr @ce in case the
+         * context was not created yet.
+         * @see @ref Configuration::setSharedContext()
+         */
+        CGLContextObj glContext() { return _context; }
+
     private:
         CGLPixelFormatObj _pixelFormat{};
         CGLContextObj _context{};
@@ -153,6 +164,8 @@ class WindowlessCglContext::Configuration {
          * limitations apply to shared OpenGL contexts, please consult the
          * OpenGL specification for details. Default is @cpp nullptr @ce, i.e.
          * no sharing.
+         * @see @ref WindowlessCglContext::glContext(),
+         *      @ref WindowlessCglApplication::glContext()
          */
         Configuration& setSharedContext(CGLContextObj context) {
             _sharedContext = context;
@@ -314,6 +327,17 @@ class WindowlessCglApplication {
          */
         virtual int exec() = 0;
 
+        /**
+         * @brief Underlying OpenGL context
+         * @m_since_latest
+         *
+         * Use in case you need to call CGL functionality directly or in order
+         * to create a shared context. Returns @cpp nullptr @ce in case the
+         * context was not created yet.
+         * @see @ref Configuration::setSharedContext()
+         */
+        CGLContextObj glContext() { return _glContext.glContext(); }
+
     protected:
         /* Nobody will need to have (and delete) WindowlessCglApplication*,
            thus this is faster than public pure virtual destructor */

src/Magnum/Platform/WindowlessEglApplication.h

@@ -120,6 +120,17 @@ class WindowlessEglContext {
          */
         bool makeCurrent();
 
+        /**
+         * @brief Underlying OpenGL context
+         * @m_since_latest
+         *
+         * Use in case you need to call EGL functionality directly or in order
+         * to create a shared context. Returns @cpp nullptr @ce in case the
+         * context was not created yet.
+         * @see @ref Configuration::setSharedContext()
+         */
+        EGLContext glContext() { return _context; }
+
     private:
         EGLDisplay _display{};
         EGLContext _context{};
@@ -266,6 +277,8 @@ class WindowlessEglContext::Configuration {
          * limitations apply to shared OpenGL contexts, please consult the
          * OpenGL specification for details. Default is `EGL_NO_CONTEXT`, i.e.
          * no sharing.
+         * @see @ref WindowlessEglContext::glContext(),
+         *      @ref WindowlessEglApplication::glContext()
          * @requires_gles Context sharing is not available in WebGL.
          */
         Configuration& setSharedContext(EGLContext context) {
@@ -521,6 +534,17 @@ class WindowlessEglApplication {
          */
         virtual int exec() = 0;
 
+        /**
+         * @brief Underlying OpenGL context
+         * @m_since_latest
+         *
+         * Use in case you need to call EGL functionality directly or in order
+         * to create a shared context. Returns @cpp nullptr @ce in case the
+         * context was not created yet.
+         * @see @ref Configuration::setSharedContext()
+         */
+        EGLContext glContext() { return _glContext.glContext(); }
+
     protected:
         /* Nobody will need to have (and delete) WindowlessEglApplication*,
            thus this is faster than public pure virtual destructor */

src/Magnum/Platform/WindowlessGlxApplication.h

@@ -140,6 +140,17 @@ class WindowlessGlxContext {
          */
         bool makeCurrent();
 
+        /**
+         * @brief Underlying OpenGL context
+         * @m_since_latest
+         *
+         * Use in case you need to call GLX functionality directly or in order
+         * to create a shared context. Returns @cpp nullptr @ce in case the
+         * context was not created yet.
+         * @see @ref Configuration::setSharedContext()
+         */
+        GLXContext glContext() { return _context; }
+
     private:
         Display* _display{};
         GLXPbuffer _pbuffer{};
@@ -249,6 +260,8 @@ class WindowlessGlxContext::Configuration {
          * limitations apply to shared OpenGL contexts, please consult the
          * OpenGL specification for details. Default is @cpp nullptr @ce, i.e.
          * no sharing.
+         * @see @ref WindowlessGlxContext::glContext(),
+         *      @ref WindowlessGlxApplication::glContext()
          */
         Configuration& setSharedContext(GLXContext ctx) {
             _sharedContext = ctx;
@@ -416,6 +429,17 @@ class WindowlessGlxApplication {
          */
         virtual int exec() = 0;
 
+        /**
+         * @brief Underlying OpenGL context
+         * @m_since_latest
+         *
+         * Use in case you need to call GLX functionality directly or in order
+         * to create a shared context. Returns @cpp nullptr @ce in case the
+         * context was not created yet.
+         * @see @ref Configuration::setSharedContext()
+         */
+        GLXContext glContext() { return _glContext.glContext(); }
+
     protected:
         /* Nobody will need to have (and delete) WindowlessGlxApplication*,
            thus this is faster than public pure virtual destructor */

src/Magnum/Platform/WindowlessWglApplication.h

@@ -134,6 +134,17 @@ class WindowlessWglContext {
          */
         bool makeCurrent();
 
+        /**
+         * @brief Underlying OpenGL context
+         * @m_since_latest
+         *
+         * Use in case you need to call WGL functionality directly or in order
+         * to create a shared context. Returns @cpp nullptr @ce in case the
+         * context was not created yet.
+         * @see @ref Configuration::setSharedContext()
+         */
+        HGLRC glContext() { return _context; }
+
     private:
         HWND _window{};
         HDC _deviceContext{};
@@ -243,6 +254,8 @@ class WindowlessWglContext::Configuration {
          * limitations apply to shared OpenGL contexts, please consult the
          * OpenGL specification for details. Default is @cpp nullptr @ce, i.e.
          * no sharing.
+         * @see @ref WindowlessWglContext::glContext(),
+         *      @ref WindowlessWglApplication::glContext()
          */
         Configuration& setSharedContext(HGLRC context) {
             _sharedContext = context;
@@ -408,6 +421,17 @@ class WindowlessWglApplication {
          */
         virtual int exec() = 0;
 
+        /**
+         * @brief Underlying OpenGL context
+         * @m_since_latest
+         *
+         * Use in case you need to call WGL functionality directly or in order
+         * to create a shared context. Returns @cpp nullptr @ce in case the
+         * context was not created yet.
+         * @see @ref Configuration::setSharedContext()
+         */
+        HGLRC glContext() { return _glContext.glContext(); }
+
     protected:
         /* Nobody will need to have (and delete) WindowlessWglApplication*,
            thus this is faster than public pure virtual destructor */

src/Magnum/Platform/WindowlessWindowsEglApplication.h

@@ -119,6 +119,17 @@ class WindowlessWindowsEglContext {
          */
         bool makeCurrent();
 
+        /**
+         * @brief Underlying OpenGL context
+         * @m_since_latest
+         *
+         * Use in case you need to call EGL functionality directly or in order
+         * to create a shared context. Returns @cpp nullptr @ce in case the
+         * context was not created yet.
+         * @see @ref Configuration::setSharedContext()
+         */
+        EGLContext glContext() { return _context; }
+
     private:
         HWND _window{};
         EGLDisplay _display{};
@@ -213,6 +224,8 @@ class WindowlessWindowsEglContext::Configuration {
          * limitations apply to shared OpenGL contexts, please consult the
          * OpenGL specification for details. Default is `EGL_NO_CONTEXT`, i.e.
          * no sharing.
+         * @see @ref WindowlessWindowsEglContext::glContext(),
+         *      @ref WindowlessWindowsEglApplication::glContext()
          */
         Configuration& setSharedContext(EGLContext context) {
             _sharedContext = context;
@@ -378,6 +391,17 @@ class WindowlessWindowsEglApplication {
          */
         virtual int exec() = 0;
 
+        /**
+         * @brief Underlying OpenGL context
+         * @m_since_latest
+         *
+         * Use in case you need to call EGL functionality directly or in order
+         * to create a shared context. Returns @cpp nullptr @ce in case the
+         * context was not created yet.
+         * @see @ref Configuration::setSharedContext()
+         */
+        EGLContext glContext() { return _glContext.glContext(); }
+
     protected:
         /* Nobody will need to have (and delete) WindowlessWindowsEglApplication*,
            thus this is faster than public pure virtual destructor */