Platform: ability to request debug context in windowless applications.

Binary AMD drivers require the user to explicitly request the debug
context on context initialization, otherwise all debug functions are
no-op. This allows us to use debug functionality in command-line utils
and, mainly, GL functionality tests.

The Windows versions are coded without testing, so I hope I did not break
something :)

src/Magnum/Platform/WindowlessGlxApplication.cpp

@@ -53,7 +53,7 @@ void WindowlessGlxApplication::createContext(const Configuration& configuration)
     if(!tryCreateContext(configuration)) std::exit(1);
 }
 
-bool WindowlessGlxApplication::tryCreateContext(const Configuration&) {
+bool WindowlessGlxApplication::tryCreateContext(const Configuration& configuration) {
     CORRADE_ASSERT(_context->version() == Version::None, "Platform::WindowlessGlxApplication::tryCreateContext(): context already created", false);
     _display = XOpenDisplay(nullptr);
 
@@ -82,7 +82,7 @@ bool WindowlessGlxApplication::tryCreateContext(const Configuration&) {
     };
     _pbuffer = glXCreatePbuffer(_display, configs[0], pbufferAttributes);
 
-    constexpr static const GLint contextAttributes[] = {
+    const GLint contextAttributes[] = {
         #ifdef MAGNUM_TARGET_GLES
         #ifdef MAGNUM_TARGET_GLES3
         GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
@@ -99,7 +99,7 @@ bool WindowlessGlxApplication::tryCreateContext(const Configuration&) {
         GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
         GLX_CONTEXT_MINOR_VERSION_ARB, 1,
         GLX_CONTEXT_PROFILE_MASK_ARB, GLX_CONTEXT_CORE_PROFILE_BIT_ARB,
-        GLX_CONTEXT_FLAGS_ARB, GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB,
+        GLX_CONTEXT_FLAGS_ARB, GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB|GLint(configuration.flags()),
         #endif
         0
     };
@@ -138,7 +138,12 @@ bool WindowlessGlxApplication::tryCreateContext(const Configuration&) {
             glXDestroyContext(_display, _glContext);
         }
 
-        _glContext = glXCreateContextAttribsARB(_display, configs[0], nullptr, True, nullptr);
+        const GLint fallbackContextAttributes[] = {
+            GLX_CONTEXT_FLAGS_ARB, GLint(configuration.flags()),
+            0
+        };
+
+        _glContext = glXCreateContextAttribsARB(_display, configs[0], nullptr, True, fallbackContextAttributes);
     }
     #endif
 

src/Magnum/Platform/WindowlessGlxApplication.h

@@ -30,6 +30,7 @@
  */
 
 #include <memory>
+#include <Corrade/Containers/EnumSet.h>
 
 #include "Magnum/OpenGL.h"
 #include <GL/glx.h>
@@ -176,7 +177,44 @@ class WindowlessGlxApplication {
 */
 class WindowlessGlxApplication::Configuration {
     public:
+        /**
+         * @brief Context flag
+         *
+         * @see @ref Flags, @ref setFlags(), @ref Context::Flag
+         */
+        enum class Flag: int {
+            Debug = GLX_CONTEXT_DEBUG_BIT_ARB   /**< Create debug context */
+        };
+
+        /**
+         * @brief Context flags
+         *
+         * @see @ref setFlags(), @ref Context::Flags
+         */
+        #ifndef DOXYGEN_GENERATING_OUTPUT
+        typedef Containers::EnumSet<Flag, GLX_CONTEXT_DEBUG_BIT_ARB> Flags;
+        #else
+        typedef Containers::EnumSet<Flag> Flags;
+        #endif
+
         constexpr /*implicit*/ Configuration() {}
+
+        /** @brief Context flags */
+        Flags flags() const { return _flags; }
+
+        /**
+         * @brief Set context flags
+         * @return Reference to self (for method chaining)
+         *
+         * Default is no flag. See also @ref Context::flags().
+         */
+        Configuration& setFlags(Flags flags) {
+            _flags = flags;
+            return *this;
+        }
+
+    private:
+        Flags _flags;
 };
 
 /** @hideinitializer

src/Magnum/Platform/WindowlessWglApplication.cpp

@@ -75,7 +75,7 @@ void WindowlessWglApplication::createContext(const Configuration& configuration)
     if(!tryCreateContext(configuration)) std::exit(1);
 }
 
-bool WindowlessWglApplication::tryCreateContext(const Configuration&) {
+bool WindowlessWglApplication::tryCreateContext(const Configuration& configuration) {
     CORRADE_ASSERT(_context->version() == Version::None, "Platform::WindowlessWglApplication::tryCreateContext(): context already created", false);
 
     /* Get device context */
@@ -104,8 +104,14 @@ bool WindowlessWglApplication::tryCreateContext(const Configuration&) {
     const int pixelFormat = ChoosePixelFormat(_deviceContext, &pfd);
     SetPixelFormat(_deviceContext, pixelFormat, &pfd);
 
+    const int attributes = {
+        WGL_CONTEXT_FLAGS_ARB, int(configuration.flags()),
+        0
+    };
+
     /* Create context and make it current */
-    _renderingContext = wglCreateContext(_deviceContext);
+    const PFNWGLCREATECONTEXTATTRIBSARBPROC wglCreateContextAttribsARB = reinterpret_cast<PFNWGLCREATECONTEXTATTRIBSARBPROC>( wglGetProcAddress(reinterpret_cast<LPCSTR>("glXCreateContextAttribsARB")));
+    _renderingContext = wglCreateContextAttribsARB(_deviceContext, 0, attributes);
     if(!_renderingContext) {
         Error() << "Platform::WindowlessWglApplication::tryCreateContext(): cannot create context:" << GetLastError();
         return false;

src/Magnum/Platform/WindowlessWglApplication.h

@@ -35,6 +35,7 @@
 #define VC_EXTRALEAN
 #endif
 #include <windows.h>
+#include <Corrade/Containers/EnumSet.h>
 
 #include "Magnum/Magnum.h"
 #include "Magnum/OpenGL.h"
@@ -177,7 +178,46 @@ class WindowlessWglApplication {
 */
 class WindowlessWglApplication::Configuration {
     public:
+        /**
+         * @brief Context flag
+         *
+         * @see @ref Flags, @ref setFlags(), @ref Context::Flag
+         */
+        enum class Flag: int {
+            Debug = WGL_CONTEXT_DEBUG_BIT_ARB   /**< Create debug context */
+        };
+
+        /**
+         * @brief Context flags
+         *
+         * @see @ref setFlags(), @ref Context::Flags
+         */
+        #ifndef DOXYGEN_GENERATING_OUTPUT
+        typedef Containers::EnumSet<Flag, WGL_CONTEXT_DEBUG_BIT_ARB> Flags;
+        #else
+        typedef Containers::EnumSet<Flag> Flags;
+        #endif
+        #endif
+
         constexpr /*implicit*/ Configuration() {}
+        ~Configuration();
+
+        /** @brief Context flags */
+        Flags flags() const { return _flags; }
+
+        /**
+         * @brief Set context flags
+         * @return Reference to self (for method chaining)
+         *
+         * Default is no flag. See also @ref Context::flags().
+         */
+        Configuration& setFlags(Flags flags) {
+            _flags = flags;
+            return *this;
+        }
+
+    private:
+        Flags _flags;
 };
 
 /** @hideinitializer

src/Magnum/Platform/WindowlessWindowsEglApplication.cpp

@@ -77,7 +77,7 @@ void WindowlessWindowsEglApplication::createContext(const Configuration& configu
     if(!tryCreateContext(configuration)) std::exit(1);
 }
 
-bool WindowlessWindowsEglApplication::tryCreateContext(const Configuration&) {
+bool WindowlessWindowsEglApplication::tryCreateContext(const Configuration& configuration) {
     CORRADE_ASSERT(_context->version() == Version::None, "Platform::WindowlessWindowsEglApplication::tryCreateContext(): context already created", false);
 
     /* Initialize */
@@ -127,7 +127,7 @@ bool WindowlessWindowsEglApplication::tryCreateContext(const Configuration&) {
         return false;
     }
 
-    static const EGLint attributes[] = {
+    const EGLint attributes[] = {
         #ifdef MAGNUM_TARGET_GLES
         EGL_CONTEXT_CLIENT_VERSION,
             #ifdef MAGNUM_TARGET_GLES3
@@ -138,7 +138,7 @@ bool WindowlessWindowsEglApplication::tryCreateContext(const Configuration&) {
             #error unsupported OpenGL ES version
             #endif
         #endif
-
+        EGL_CONTEXT_FLAGS_KHR, EGLint(configuration.flags()),
         EGL_NONE
     };
 

src/Magnum/Platform/WindowlessWindowsEglApplication.h

@@ -36,6 +36,8 @@
 #endif
 #include <windows.h>
 #include <EGL/egl.h>
+#include <EGL/eglext.h>
+#include <Corrade/Containers/EnumSet.h>
 
 #include "Magnum/Magnum.h"
 #include "Magnum/OpenGL.h"
@@ -180,7 +182,44 @@ class WindowlessWindowsEglApplication {
 */
 class WindowlessWindowsEglApplication::Configuration {
     public:
+        /**
+         * @brief Context flag
+         *
+         * @see @ref Flags, @ref setFlags(), @ref Context::Flag
+         */
+        enum class Flag: int {
+            Debug = EGL_CONTEXT_OPENGL_DEBUG_BIT_KHR    /**< Create debug context */
+        };
+
+        /**
+         * @brief Context flags
+         *
+         * @see @ref setFlags(), @ref Context::Flags
+         */
+        #ifndef DOXYGEN_GENERATING_OUTPUT
+        typedef Containers::EnumSet<Flag, EGL_CONTEXT_OPENGL_DEBUG_BIT_KHR> Flags;
+        #else
+        typedef Containers::EnumSet<Flag> Flags;
+        #endif
+
         constexpr /*implicit*/ Configuration() {}
+
+        /** @brief Context flags */
+        Flags flags() const { return _flags; }
+
+        /**
+         * @brief Set context flags
+         * @return Reference to self (for method chaining)
+         *
+         * Default is no flag. See also @ref Context::flags().
+         */
+        Configuration& setFlags(Flags flags) {
+            _flags = flags;
+            return *this;
+        }
+
+    private:
+        Flags _flags;
 };
 
 /** @hideinitializer