Added an experiment.

wpf/build.bat

@@ -0,0 +1,3 @@
+cl /clr /AI "c:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0" wpf.cpp /link /dll /out:wpf.dll ole32.lib
+
+cl /Tc program.c /link /out:program.exe wpf.lib

wpf/program.c

@@ -0,0 +1,22 @@
+// 24 november 2015
+#include <stdio.h>
+#include "wpf.h"
+
+static void onClosing(wpfWindow *w, void *data)
+{
+	printf("exiting\n");
+	wpfQuit();
+}
+
+int main(void)
+{
+	wpfWindow *w;
+
+	wpfInit();
+	w = wpfNewWindow("Hi", 320, 240);
+	wpfWindowOnClosing(w, onClosing, NULL);
+
+	wpfRun();
+	printf("out\n");
+	return 0;
+}

wpf/wpf.cpp

@@ -0,0 +1,88 @@
+// 24 november 2015
+#define UNICODE
+#define _UNICODE
+#include <windows.h>
+#include <vcclr.h>
+#define EXPORT __declspec(dllexport)
+#include "wpf.h"
+
+#using <System.dll>
+#using <WindowsBase.dll>
+#using <PresentationCore.dll>
+#using <PresentationFramework.dll>
+using namespace System;
+using namespace System::ComponentModel;
+using namespace System::Windows;
+
+ref class windowEvents {
+public:
+	wpfWindow *w;
+	// TODO the using namespace above doesn't work?
+	void closingEvent(Object ^sender, CancelEventArgs ^e);
+};
+
+struct wpfWindow {
+	gcroot<Window ^> window;
+	gcroot<windowEvents ^> events;
+	void (*onClosing)(wpfWindow *, void *);
+	void *onClosingData;
+};
+
+void windowEvents::closingEvent(Object ^sender, CancelEventArgs ^e)
+{
+	(*(this->w->onClosing))(this->w, this->w->onClosingData);
+}
+
+wpfWindow *wpfNewWindow(const char *title, int width, int height)
+{
+	wpfWindow *w;
+
+	w = new wpfWindow;
+
+	w->window = gcnew Window();
+	w->window->Title = gcnew String(title);
+	w->window->Width = width;
+	w->window->Height = height;
+
+	w->events = gcnew windowEvents();
+	w->events->w = w;
+	w->window->Closing += gcnew CancelEventHandler(w->events, &windowEvents::closingEvent);
+
+	w->window->Show();
+
+	return w;
+}
+
+void wpfWindowOnClosing(wpfWindow *w, void (*f)(wpfWindow *w, void *data), void *data)
+{
+	w->onClosing = f;
+	w->onClosingData = data;
+}
+
+static gcroot<Application ^> app;
+
+void wpfInit(void)
+{
+	HRESULT hr;
+
+	// see http://stackoverflow.com/questions/24348205/how-do-i-solve-this-com-issue-in-c
+	// we MUST be running STA
+	// .net initializes as MTA for some stupid reason
+	// TODO https://msdn.microsoft.com/en-us/library/5s8ee185%28v=vs.71%29.aspx use CoInitializeEx()?
+	hr = CoInitialize(NULL);
+	if (hr != S_OK && hr != S_FALSE)
+		DebugBreak();
+
+	app = gcnew Application();
+}
+
+void wpfRun(void)
+{
+	app->Run();
+	CoUninitialize();
+}
+
+void wpfQuit(void)
+{
+	app->Shutdown();
+}

wpf/wpf.h

@@ -0,0 +1,22 @@
+// 24 november 2015
+
+#ifndef EXPORT
+#define EXPORT __declspec(dllimport)
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct wpfWindow wpfWindow;
+
+extern EXPORT wpfWindow *wpfNewWindow(const char *title, int width, int height);
+extern EXPORT void wpfWindowOnClosing(wpfWindow *w, void (*f)(wpfWindow *w, void *data), void *data);
+
+extern EXPORT void wpfInit(void);
+extern EXPORT void wpfRun(void);
+extern EXPORT void wpfQuit(void);
+
+#ifdef __cplusplus
+}
+#endif

wpf/wpf.vcxproj

@@ -0,0 +1,44 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- 24 november 2015 -->
+<Project DefaultTargets="Build" ToolsVersion="12.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+
+<!-- TODO target name -->
+
+<!-- TODO make sure all cl flags we care about are present -->
+
+<PropertyGroup Label="Configuration">
+	<TargetFrameworkVersion>v3.0</TargetFrameworkVersion>
+	<ConfigurationType>DynamicLibrary</ConfigurationType>
+	<UseDebugLibraries>true</UseDebugLibraries>
+	<PlatformToolset>v120</PlatformToolset>
+	<CLRSupport>true</CLRSupport>
+	<CharacterSet>Unicode</CharacterSet>
+	<LinkIncremental>false</LinkIncremental>
+</PropertyGroup>
+
+<!-- TODO make this unnecessary -->
+<Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+
+<ItemDefinitionGroup>
+	<ClCompile>
+		<WarningLevel>Level3</WarningLevel>
+		<!-- TODO no precompiled headers -->
+	</ClCompile>
+	<Link>
+		<GenerateDebugInformation>true</GenerateDebugInformation>
+		<AdditionalDependencies />
+	</Link>
+</ItemDefinitionGroup>
+
+<ItemGroup>
+	<Reference Include="System" />
+	<Reference Include="WindowsBase" />
+	<Reference Include="PresentationCore" />
+	<Reference Include="PresentationFramework" />
+
+	<ClInclude Include="wpf.h" />
+
+	<ClCompile Include="wpf.cpp" />
+</ItemGroup>
+
+</Project>

wpf/xtest.cpp

@@ -0,0 +1,17 @@
+// 24 november 2015
+#using <System.dll>
+#using <WindowsBase.dll>
+#using <PresentationCore.dll>
+#using <PresentationFramework.dll>
+using namespace System;
+using namespace System::ComponentModel;
+
+int main(void)
+{
+	System::ComponentModel::CancelEventArgs ^e;
+
+	e = gcnew CancelEventArgs();
+	e->Cancel = true;
+	System::Console::WriteLine(e->Cancel);
+	return 0;
+}