Attempted to split out the STA code from the rest of the build. This is a mess. MSBuild might not be sufficient here.

wpf/sta.c

@@ -0,0 +1,35 @@
+// 25 november 2015
+#include "../windows/winapi.h"
+#include "../ui.h"
+
+// If we don't set up the current thread otherwise, the first time .net tries to call out to unmanaged code, it will automatically set up a MTA for COM.
+// This is not what we want; we need a STA instead.
+// Since we're not in control of main(), we can't stick a [STAThread] on it, so we have to do it ourselves.
+// This is a separate .c file for two reasons:
+// 1) To avoid the unmanaged jump that a call to CoInitialize() would do (it seems to detect a call to CoInitialize()/CoInitializeEx() but let's not rely on it)
+// 2) To avoid mixing Windows API headers with .net
+// See also http://stackoverflow.com/questions/24348205/how-do-i-solve-this-com-issue-in-c
+
+extern void initWPF(void);
+//extern void uninitWPF(void);
+
+void wpfInit(void)
+{
+	HRESULT hr;
+
+	// 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();
+
+	// now do the rest of initialization on the managed side
+	initWPF();
+}
+
+/*TODO
+void uiUninit(void)
+{
+	uninitWPF();
+	CoUninitialize();
+}
+*/

wpf/wpf.cpp

@@ -1,7 +1,4 @@
 // 24 november 2015
-#define UNICODE
-#define _UNICODE
-#include <windows.h>
 #include <vcclr.h>
 #define EXPORT __declspec(dllexport)
 #include "wpf.h"
@@ -61,25 +58,15 @@ void wpfWindowOnClosing(wpfWindow *w, void (*f)(wpfWindow *w, void *data), void
 
 static gcroot<Application ^> app;
 
-void wpfInit(void)
+// wpfInit() is in sta.c; see that or details.
+extern "C" void initWPF(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)

wpf/wpf.vcxproj

@@ -3,6 +3,8 @@
 
 <!-- DO NOT EDIT IN VISUAL STUDIO! -->
 
+<!-- TODO go through all possible command line options and make sure the ones we want are enabled -->
+
 <Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
 
 <ItemGroup Label="ProjectConfigurations">
@@ -38,17 +40,19 @@
 	<LinkIncremental>false</LinkIncremental>
 	<TargetName>libui</TargetName>
 	<!-- TODO will these work from any directory? -->
-	<OutDir>..\out</OutDir>
+	<OutDir>..\out\</OutDir>
-	<IntDir>..\.obj</IntDir>
+	<IntDir>..\.obj\</IntDir>
 	<EnableManagedIncrementalBuild>false</EnableManagedIncrementalBuild>
-<!--	<CustomBuildBeforeTargets>Link</CustomBuildBeforeTargets>-->
+	<CustomBuildBeforeTargets>Link</CustomBuildBeforeTargets>
 </PropertyGroup>
 
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
 	<ClCompile>
 		<WarningLevel>EnableAllWarnings</WarningLevel>
 		<PrecompiledHeader>NotUsing</PrecompiledHeader>
-<!--		<AdditionalOptions>additional compiler options %(AdditionalOptions)</AdditionalOptions>-->
+		<!-- TODO there's a better way for this -->
+		<!-- do not warn about unreferended parameters -->
+		<AdditionalOptions>/wd4100</AdditionalOptions>
 	</ClCompile>
 	<Link>
 		<GenerateDebugInformation>true</GenerateDebugInformation>
@@ -57,8 +61,14 @@
 <!--TODO		<MinimumRequiredVersion>600</MinimumRequiredVersion>-->
 <!--		<AdditionalOptions>additional linker options %(AdditionalOptions)</AdditionalOptions>-->
 	</Link>
+	<!-- TODO convert to a build rule -->
+	<!-- TODO use /Wall instead of /W4 -->
 	<CustomBuildStep>
-		<Command>extra command</Command>
+		<!-- TODO /MDd, /MTd, /EHa? -->
+		<!-- TODO /RTC1 /RTCc /RTCs /RTCu /sdl -->
+		<Command>cl sta.c /c /TC /analyze /bigobj /nologo /W4 /Wp64 /Zi /wd4100 /Fo$(IntDir)sta.obj</Command>
+		<Inputs>sta.c</Inputs>
+		<Outputs>$(IntDir)sta.obj</Outputs>
 	</CustomBuildStep>
 </ItemDefinitionGroup>
 
@@ -71,6 +81,8 @@
 	<ClInclude Include="wpf.h" />
 
 	<ClCompile Include="wpf.cpp" />
+
+	<Link Include="$(IntDir)sta.obj" />
 </ItemGroup>
 
 <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />