Enable backend switching for Windows Viewer

tools/viewer/sk_app/win/Window_win.cpp

 /*
 * Copyright 2016 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #include "Window_win.h"
 
 #include <tchar.h>
@@ skipping 15 matching lines @@
     if (!window->init(hInstance)) {
         delete window;
         return nullptr;
     }
 
     return window;
 }
 
 LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);
 
+
 bool Window_win::init(HINSTANCE hInstance) {
     fHInstance = hInstance ? hInstance : GetModuleHandle(nullptr);
 
-    WNDCLASSEX wcex;
     // The main window class name
     static const TCHAR gSZWindowClass[] = _T("SkiaApp");
 
-    wcex.cbSize = sizeof(WNDCLASSEX);
+    static WNDCLASSEX wcex;
+    static bool wcexInit = false;
+    if (!wcexInit) {
+        wcex.cbSize = sizeof(WNDCLASSEX);
 
-    wcex.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
-    wcex.lpfnWndProc = WndProc;
-    wcex.cbClsExtra = 0;
-    wcex.cbWndExtra = 0;
-    wcex.hInstance = fHInstance;
-    wcex.hIcon = LoadIcon(fHInstance, (LPCTSTR)IDI_WINLOGO);
-    wcex.hCursor = LoadCursor(nullptr, IDC_ARROW);;
-    wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
-    wcex.lpszMenuName = nullptr;
-    wcex.lpszClassName = gSZWindowClass;
-    wcex.hIconSm = LoadIcon(fHInstance, (LPCTSTR)IDI_WINLOGO);;
+        wcex.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
+        wcex.lpfnWndProc = WndProc;
+        wcex.cbClsExtra = 0;
+        wcex.cbWndExtra = 0;
+        wcex.hInstance = fHInstance;
+        wcex.hIcon = LoadIcon(fHInstance, (LPCTSTR)IDI_WINLOGO);
+        wcex.hCursor = LoadCursor(nullptr, IDC_ARROW);;
+        wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
+        wcex.lpszMenuName = nullptr;
+        wcex.lpszClassName = gSZWindowClass;
+        wcex.hIconSm = LoadIcon(fHInstance, (LPCTSTR)IDI_WINLOGO);;
 
-    if (!RegisterClassEx(&wcex)) {
-        return false;
+        if (!RegisterClassEx(&wcex)) {
+            return false;
+        }
+        wcexInit = true;
     }
 
    /*
     if (fullscreen)
     {
         DEVMODE dmScreenSettings;
         // If full screen set the screen to maximum size of the users desktop and 32bit.
         memset(&dmScreenSettings, 0, sizeof(dmScreenSettings));
         dmScreenSettings.dmSize = sizeof(dmScreenSettings);
         dmScreenSettings.dmPelsWidth = (unsigned long)width;
@@ skipping 99 matching lines @@
 
     switch (message) {
         case WM_PAINT:
             hdc = BeginPaint(hWnd, &ps);
             window->onPaint();
             EndPaint(hWnd, &ps);
             eventHandled = true;
             break;
 
         case WM_CLOSE:
-        case WM_DESTROY:
             PostQuitMessage(0);
             eventHandled = true;
             break;
 
         case WM_ACTIVATE:
             // disable/enable rendering here, depending on wParam != WA_INACTIVE
             break;
 
         case WM_SIZE:
             window->onResize(LOWORD(lParam), HIWORD(lParam));
@@ skipping 92 matching lines @@
     }
 
     return (SkToBool(fWindowContext));
 }
 
 void Window_win::onInval() {
     InvalidateRect(fHWnd, nullptr, false);
 }
 
 }   // namespace sk_app