Enable backend switching for Windows Viewer

tools/viewer/Viewer.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 "Viewer.h"
 
 #include "GMSlide.h"
@@ skipping 42 matching lines @@
                "[~][^]substring[$] [...] of bench name to run.\n"
                "Multiple matches may be separated by spaces.\n"
                "~ causes a matching bench to always be skipped\n"
                "^ requires the start of the bench to match\n"
                "$ requires the end of the bench to match\n"
                "^ and $ requires an exact match\n"
                "If a bench does not match any list entry,\n"
                "it is skipped unless some list entry starts with ~");
 
 #ifdef SK_VULKAN
-#    define BACKENDS_STR "\"sw\", \"gl\", and \"vulkan\""
+#    define BACKENDS_STR "\"sw\", \"gl\", and \"vk\""
 #else
 #    define BACKENDS_STR "\"sw\" and \"gl\""
 #endif
 
 #ifdef SK_BUILD_FOR_ANDROID
 DEFINE_string(skps, "/data/local/tmp/skia", "Directory to read skps from.");
 DEFINE_string(jpgs, "/data/local/tmp/skia", "Directory to read jpgs from.");
 #else
 DEFINE_string(skps, "skps", "Directory to read skps from.");
 DEFINE_string(jpgs, "jpgs", "Directory to read jpgs from.");
@@ skipping 99 matching lines @@
         this->setupCurrentSlide(previousSlide);
     });
     fCommands.addCommand(Window::Key::kUp, "Up", "Transform", "Zoom in", [this]() {
         this->changeZoomLevel(1.f / 32.f);
         fWindow->inval();
     });
     fCommands.addCommand(Window::Key::kDown, "Down", "Transform", "Zoom out", [this]() {
         this->changeZoomLevel(-1.f / 32.f);
         fWindow->inval();
     });
-#if 0  // this doesn't seem to work on any platform right now
-#ifndef SK_BUILD_FOR_ANDROID
+#ifdef SK_BUILD_FOR_WIN
     fCommands.addCommand('d', "Modes", "Change rendering backend", [this]() {
+        if (sk_app::Window::kRaster_BackendType == fBackendType) {
+            fBackendType = sk_app::Window::kNativeGL_BackendType;
+#ifdef SK_VULKAN
+        } else if (sk_app::Window::kNativeGL_BackendType == fBackendType) {
+            fBackendType = sk_app::Window::kVulkan_BackendType;
+#endif
+        } else {
+            fBackendType = sk_app::Window::kRaster_BackendType;
+        }
+
         fWindow->detach();
 
+#ifdef SK_VULKAN
+        // Switching from OpenGL to Vulkan in the same window is problematic at this point,
+        // so we just delete the window and recreate it.
+        // On Windows, only tearing down the window when going from OpenGL to Vulkan works fine.
+        // On Linux, we may need to tear down the window for the Vulkan to OpenGL case as well.
         if (sk_app::Window::kVulkan_BackendType == fBackendType) {
-            fBackendType = sk_app::Window::kNativeGL_BackendType;
-        } 
-        // TODO: get Vulkan -> OpenGL working on Windows without swapchain creation failure
-        //else if (sk_app::Window::kNativeGL_BackendType == fBackendType) {
-        //    fBackendType = sk_app::Window::kVulkan_BackendType;
-        //}
+            delete fWindow;
+            fWindow = Window::CreateNativeWindow(nullptr);
 
+            // re-register callbacks
+            fCommands.attach(fWindow);
+            fWindow->registerPaintFunc(on_paint_handler, this);
+            fWindow->registerTouchFunc(on_touch_handler, this);
+            fWindow->registerUIStateChangedFunc(on_ui_state_changed_handler, this);
+        }
+#endif
         fWindow->attach(fBackendType, DisplayParams());
+
         this->updateTitle();
         fWindow->inval();
+        fWindow->show();
     });
 #endif
-#endif
 
     // set up slides
     this->initSlides();
 
     fAnimTimer.run();
 
     // set up first frame
     fCurrentSlide = 0;
     setupCurrentSlide(-1);
 
@@ skipping 416 matching lines @@
             updateUIState();
         }
     } else if (stateName.equals(kRefreshStateName)) {
         // This state is actually NOT in the UI state.
         // We use this to allow Android to quickly set bool fRefresh.
         fRefresh = stateValue.equals(kON);
     } else {
         SkDebugf("Unknown stateName: %s", stateName.c_str());
     }
 }