Fix flicker when changing backend on iOS viewer

This is the same fix from: https://skia-review.googlesource.com/c/skia/+/107941

Change-Id: I1367b1fc466cecbc2733b4e337376ce9f48cb6d8
Reviewed-on: https://skia-review.googlesource.com/107980
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

tools/sk_app/ios/GLWindowContext_ios.cpp

@@ -27,7 +27,7 @@ public:
     void onSwapBuffers() override;
 
     sk_sp<const GrGLInterface> onInitializeContext() override;
-    void onDestroyContext() override;
+    void onDestroyContext() override {}
 
 private:
     SDL_Window*   fWindow;
@@ -39,7 +39,7 @@ private:
 GLWindowContext_ios::GLWindowContext_ios(const IOSWindowInfo& info, const DisplayParams& params)
     : INHERITED(params)
     , fWindow(info.fWindow)
-    , fGLContext(nullptr) {
+    , fGLContext(info.fGLContext) {
 
     // any config code here (particularly for msaa)?
 
@@ -52,12 +52,7 @@ GLWindowContext_ios::~GLWindowContext_ios() {
 
 sk_sp<const GrGLInterface> GLWindowContext_ios::onInitializeContext() {
     SkASSERT(fWindow);
-
-    fGLContext = SDL_GL_CreateContext(fWindow);
-    if (!fGLContext) {
-        SkDebugf("%s\n", SDL_GetError());
-        return nullptr;
-    }
+    SkASSERT(fGLContext);
 
     if (0 == SDL_GL_MakeCurrent(fWindow, fGLContext)) {
         glClearStencil(0);
@@ -77,15 +72,6 @@ sk_sp<const GrGLInterface> GLWindowContext_ios::onInitializeContext() {
     return GrGLMakeNativeInterface();
 }
 
-void GLWindowContext_ios::onDestroyContext() {
-    if (!fWindow || !fGLContext) {
-        return;
-    }
-    SDL_GL_DeleteContext(fGLContext);
-    fGLContext = nullptr;
-}
-
-
 void GLWindowContext_ios::onSwapBuffers() {
     if (fWindow && fGLContext) {
         SDL_GL_SwapWindow(fWindow);

tools/sk_app/ios/RasterWindowContext_ios.cpp

@@ -64,12 +64,7 @@ RasterWindowContext_ios::~RasterWindowContext_ios() {
 
 sk_sp<const GrGLInterface> RasterWindowContext_ios::onInitializeContext() {
     SkASSERT(fWindow);
-
-    fGLContext = SDL_GL_CreateContext(fWindow);
-    if (!fGLContext) {
-        SkDebugf("%s\n", SDL_GetError());
-        return nullptr;
-    }
+    SkASSERT(fGLContext);
 
     if (0 == SDL_GL_MakeCurrent(fWindow, fGLContext)) {
         glClearStencil(0);
@@ -95,12 +90,7 @@ sk_sp<const GrGLInterface> RasterWindowContext_ios::onInitializeContext() {
 }
 
 void RasterWindowContext_ios::onDestroyContext() {
-    if (!fWindow || !fGLContext) {
-        return;
-    }
     fBackbufferSurface.reset(nullptr);
-    SDL_GL_DeleteContext(fGLContext);
-    fGLContext = nullptr;
 }
 
 sk_sp<SkSurface> RasterWindowContext_ios::getBackbufferSurface() { return fBackbufferSurface; }

tools/sk_app/ios/WindowContextFactory_ios.h

@@ -20,6 +20,7 @@ namespace window_context_factory {
 
 struct IOSWindowInfo {
     SDL_Window*   fWindow;
+    SDL_GLContext fGLContext;
 };
 
 inline WindowContext* NewVulkanForIOS(const IOSWindowInfo&, const DisplayParams&) {

tools/sk_app/ios/Window_ios.cpp

@@ -71,10 +71,22 @@ bool Window_ios::initWindow() {
     fWindowID = SDL_GetWindowID(fWindow);
     gWindowMap.add(this);
 
+    fGLContext = SDL_GL_CreateContext(fWindow);
+    if (!fGLContext) {
+        SkDebugf("%s\n", SDL_GetError());
+        this->closeWindow();
+        return false;
+    }
+
     return true;
 }
 
 void Window_ios::closeWindow() {
+    if (fGLContext) {
+        SDL_GL_DeleteContext(fGLContext);
+        fGLContext = nullptr;
+    }
+
     if (fWindow) {
         gWindowMap.remove(fWindowID);
         SDL_DestroyWindow(fWindow);
@@ -251,6 +263,7 @@ bool Window_ios::attach(BackendType attachType) {
 
     window_context_factory::IOSWindowInfo info;
     info.fWindow = fWindow;
+    info.fGLContext = fGLContext;
     switch (attachType) {
         case kRaster_BackendType:
             fWindowContext = NewRasterForIOS(info, fRequestedDisplayParams);

tools/sk_app/ios/Window_ios.h

@@ -18,7 +18,12 @@ namespace sk_app {
 
 class Window_ios : public Window {
 public:
-    Window_ios() : INHERITED(), fWindow(nullptr), fWindowID(0), fMSAASampleCount(1) {}
+    Window_ios()
+            : INHERITED()
+            , fWindow(nullptr)
+            , fWindowID(0)
+            , fGLContext(nullptr)
+            , fMSAASampleCount(1) {}
     ~Window_ios() override { this->closeWindow(); }
 
     bool initWindow();
@@ -49,6 +54,7 @@ private:
 
     SDL_Window*   fWindow;
     Uint32        fWindowID;
+    SDL_GLContext fGLContext;
 
     int          fMSAASampleCount;