python: expose Platform::GLContext as platform.{egl,wgl,glx}.Context.

Turning the link-time decision to a runtime decision. Crazily enough
this seems to work with no duplicate symbol issues (apart from having
to expose a function-local subclass).

src/python/magnum/platform/egl.cpp

@@ -25,6 +25,7 @@
 
 #include <pybind11/pybind11.h>
 #include <Magnum/Platform/WindowlessEglApplication.h>
+#include <Magnum/Platform/GLContext.h>
 
 #include "magnum/bootstrap.h"
 #include "magnum/platform/windowlessapplication.h"
@@ -68,6 +69,13 @@ void egl(py::module_& m) {
     py::class_<PyWindowlessApplication, ApplicationHolder<PyWindowlessApplication>> windowlessEglApplication{m, "WindowlessApplication", "Windowless EGL application"};
 
     windowlessapplication(windowlessEglApplication);
+
+    /* Exposing a subclass to avoid the same type being exposed in multiple
+       (glx, egl...) modules. */
+    struct PyContext: Platform::GLContext {};
+    py::class_<PyContext> glContext{m, "Context", "EGL-specific Magnum OpenGL context"};
+
+    context(glContext);
 }
 
 }}

src/python/magnum/platform/glx.cpp

@@ -25,6 +25,7 @@
 
 #include <pybind11/pybind11.h>
 #include <Magnum/Platform/WindowlessGlxApplication.h>
+#include <Magnum/Platform/GLContext.h>
 
 #include "magnum/bootstrap.h"
 #include "magnum/platform/windowlessapplication.h"
@@ -68,6 +69,13 @@ void glx(py::module_& m) {
     py::class_<PyWindowlessApplication, ApplicationHolder<PyWindowlessApplication>> windowlessGlxApplication{m, "WindowlessApplication", "Windowless GLX application"};
 
     windowlessapplication(windowlessGlxApplication);
+
+    /* Exposing a subclass to avoid the same type being exposed in multiple
+       (glx, egl...) modules. */
+    struct PyContext: Platform::GLContext {};
+    py::class_<PyContext> glContext{m, "Context", "GLX-specific Magnum OpenGL context"};
+
+    context(glContext);
 }
 
 }}

src/python/magnum/platform/wgl.cpp

@@ -25,6 +25,7 @@
 
 #include <pybind11/pybind11.h>
 #include <Magnum/Platform/WindowlessWglApplication.h>
+#include <Magnum/Platform/GLContext.h>
 
 #include "magnum/bootstrap.h"
 #include "magnum/platform/windowlessapplication.h"
@@ -68,6 +69,13 @@ void wgl(py::module_& m) {
     py::class_<PyWindowlessApplication, ApplicationHolder<PyWindowlessApplication>> windowlessWglApplication{m, "WindowlessApplication", "Windowless WGL application"};
 
     windowlessapplication(windowlessWglApplication);
+
+    /* Exposing a subclass to avoid the same type being exposed in multiple
+       (glx, egl...) modules. */
+    struct PyContext: Platform::GLContext {};
+    py::class_<PyContext> glContext{m, "Context", "WGL-specific Magnum OpenGL context"};
+
+    context(glContext);
 }
 
 }}

src/python/magnum/platform/windowlessapplication.h

@@ -46,4 +46,11 @@ template<class T, class Holder> void windowlessapplication(py::class_<T, Holder>
         ;
 }
 
+template<class T> void context(py::class_<T>& c) {
+    c
+        .def(py::init())
+        /** @todo delayed creation */
+        ;
+}
+
 }}