diff --git a/src/gx/CGxDevice.cpp b/src/gx/CGxDevice.cpp
index 96fa81b..3af9cd8 100644
--- a/src/gx/CGxDevice.cpp
+++ b/src/gx/CGxDevice.cpp
@@ -198,9 +198,8 @@ const CGxCaps& CGxDevice::Caps() const {
     return this->m_caps;
 }
 
-int32_t CGxDevice::DeviceCreate(long (*windowProc)(void*, uint32_t, uint32_t, long), const CGxFormat& format) {
-    // TODO
-    // this->m_windowProc = windowProc;
+int32_t CGxDevice::DeviceCreate(int32_t (*windowProc)(void* window, uint32_t message, uint32_t wparam, int32_t lparam), const CGxFormat& format) {
+    this->m_windowProc = windowProc;
 
     return this->DeviceSetFormat(format);
 }
diff --git a/src/gx/CGxDevice.hpp b/src/gx/CGxDevice.hpp
index bd07002..11f8196 100644
--- a/src/gx/CGxDevice.hpp
+++ b/src/gx/CGxDevice.hpp
@@ -71,6 +71,7 @@ class CGxDevice {
         CGxCaps m_caps;
         int32_t m_shaderProfiles[GxShTargets_Last] = { 6, 0, 0, 0, 12, 0 }; // TODO placeholder
         TSHashTable<CGxShader, HASHKEY_STRI> m_shaderList[GxShTargets_Last];
+        int32_t (*m_windowProc)(void* window, uint32_t message, uint32_t wparam, int32_t lparam) = nullptr;
         int32_t m_context = 0;
         int32_t intF5C = 0;
         int32_t m_windowVisible = 0;
@@ -104,7 +105,7 @@ class CGxDevice {
         virtual void ITexMarkAsUpdated(CGxTex*) = 0;
         virtual void IRsSendToHw(EGxRenderState) = 0;
         virtual void ICursorCreate(const CGxFormat& format);
-        virtual int32_t DeviceCreate(long (*)(void*, uint32_t, uint32_t, long), const CGxFormat&);
+        virtual int32_t DeviceCreate(int32_t (*windowProc)(void* window, uint32_t message, uint32_t wparam, int32_t lparam), const CGxFormat&);
         virtual int32_t DeviceSetFormat(const CGxFormat&);
         virtual void DeviceWM(EGxWM wm, uintptr_t param1, uintptr_t param2) = 0;
         virtual void CapsWindowSize(CRect&) = 0;
diff --git a/src/gx/Device.cpp b/src/gx/Device.cpp
index 799eb41..173b3d5 100644
--- a/src/gx/Device.cpp
+++ b/src/gx/Device.cpp
@@ -4,7 +4,7 @@
 
 CGxDevice* g_theGxDevicePtr = nullptr;
 
-CGxDevice* GxDevCreate(EGxApi api, long (*windowProc)(void*, uint32_t, uint32_t, long), const CGxFormat& format) {
+CGxDevice* GxDevCreate(EGxApi api, int32_t (*windowProc)(void* window, uint32_t message, uint32_t wparam, int32_t lparam), const CGxFormat& format) {
     CGxDevice* device;
 
     #if defined(WHOA_SYSTEM_WIN)
diff --git a/src/gx/Device.hpp b/src/gx/Device.hpp
index db2e9ab..1a041e4 100644
--- a/src/gx/Device.hpp
+++ b/src/gx/Device.hpp
@@ -9,7 +9,7 @@ class CGxFormat;
 
 extern CGxDevice* g_theGxDevicePtr;
 
-CGxDevice* GxDevCreate(EGxApi, long (*)(void*, uint32_t, uint32_t, long), const CGxFormat&);
+CGxDevice* GxDevCreate(EGxApi api, int32_t (*windowProc)(void* window, uint32_t message, uint32_t wparam, int32_t lparam), const CGxFormat& format);
 
 EGxApi GxDevApi(void);
 
diff --git a/src/gx/d3d/CGxDeviceD3d.cpp b/src/gx/d3d/CGxDeviceD3d.cpp
index d14f202..c264206 100644
--- a/src/gx/d3d/CGxDeviceD3d.cpp
+++ b/src/gx/d3d/CGxDeviceD3d.cpp
@@ -357,7 +357,9 @@ LRESULT CGxDeviceD3d::WindowProcD3d(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM
         break;
     }
 
-    // TODO
+    if (device && device->m_windowProc) {
+        return device->m_windowProc(hWnd, uMsg, wParam, lParam);
+    }
 
     return DefWindowProc(hWnd, uMsg, wParam, lParam);
 }
@@ -428,7 +430,7 @@ int32_t CGxDeviceD3d::CreatePoolAPI(CGxPool* pool) {
     return 1;
 }
 
-int32_t CGxDeviceD3d::DeviceCreate(long (*windowProc)(void*, uint32_t, uint32_t, long), const CGxFormat& format) {
+int32_t CGxDeviceD3d::DeviceCreate(int32_t (*windowProc)(void* window, uint32_t message, uint32_t wparam, int32_t lparam), const CGxFormat& format) {
     this->m_ownhwnd = 1;
 
     // TODO gamma ramp
diff --git a/src/gx/d3d/CGxDeviceD3d.hpp b/src/gx/d3d/CGxDeviceD3d.hpp
index 9ea7608..43771f7 100644
--- a/src/gx/d3d/CGxDeviceD3d.hpp
+++ b/src/gx/d3d/CGxDeviceD3d.hpp
@@ -241,7 +241,7 @@ class CGxDeviceD3d : public CGxDevice {
     // Virtual member functions
     virtual void ITexMarkAsUpdated(CGxTex* texId);
     virtual void IRsSendToHw(EGxRenderState which);
-    virtual int32_t DeviceCreate(long (*windowProc)(void*, uint32_t, uint32_t, long), const CGxFormat& format);
+    virtual int32_t DeviceCreate(int32_t (*windowProc)(void* window, uint32_t message, uint32_t wparam, int32_t lparam), const CGxFormat& format);
     virtual int32_t DeviceSetFormat(const CGxFormat& format);
     virtual void DeviceWM(EGxWM wm, uintptr_t param1, uintptr_t param2);
     virtual void CapsWindowSize(CRect& dst);
diff --git a/src/gx/gll/CGxDeviceGLL.cpp b/src/gx/gll/CGxDeviceGLL.cpp
index 951e305..19f97f1 100644
--- a/src/gx/gll/CGxDeviceGLL.cpp
+++ b/src/gx/gll/CGxDeviceGLL.cpp
@@ -140,7 +140,7 @@ void CGxDeviceGLL::CapsWindowSizeInScreenCoords(CRect& dst) {
     }
 }
 
-int32_t CGxDeviceGLL::DeviceCreate(long (*windowProc)(void*, uint32_t, uint32_t, long), const CGxFormat& format) {
+int32_t CGxDeviceGLL::DeviceCreate(int32_t (*windowProc)(void* window, uint32_t message, uint32_t wparam, int32_t lparam), const CGxFormat& format) {
     CGRect rect;
     Rect* bounds;
     Rect* zoomedBounds = GetSavedZoomedWindowBounds();
diff --git a/src/gx/gll/CGxDeviceGLL.hpp b/src/gx/gll/CGxDeviceGLL.hpp
index 73b2b41..d9de398 100644
--- a/src/gx/gll/CGxDeviceGLL.hpp
+++ b/src/gx/gll/CGxDeviceGLL.hpp
@@ -29,7 +29,7 @@ class CGxDeviceGLL : public CGxDevice {
         // Virtual member functions
         virtual void ITexMarkAsUpdated(CGxTex*);
         virtual void IRsSendToHw(EGxRenderState);
-        virtual int32_t DeviceCreate(long (*)(void*, uint32_t, uint32_t, long), const CGxFormat&);
+        virtual int32_t DeviceCreate(int32_t (*windowProc)(void* window, uint32_t message, uint32_t wparam, int32_t lparam), const CGxFormat&);
         virtual int32_t DeviceSetFormat(const CGxFormat&);
         virtual void DeviceWM(EGxWM wm, uintptr_t param1, uintptr_t param2) {};
         virtual void CapsWindowSize(CRect&);