Blank screen is displayed when launching app on Evas GL

[bbrto21]

Originally posted at : flutter-tizen/plugins#266 by @swift-kim

Even without splash screen, when launching app newly on wearable, a blank screen is displayed once for a while.
If you set elm_win_alpha_set as a true, it may seem to be solved, but it is not right to always treat it as transparent(This may affect performance badly).

Related discussions

• [flutter_splash_tizen] Initial implementation plugins#266 (This PR wants this issue to be resolved.)
• Remove background and set alpha as true on Evas gl #216 (Transparent window is not a perfect solution.)
• Remove background and set alpha as true on Evas gl #216 (comment) (TizenVsyncWaiter use a unmanaged API.)

[bbrto21]

I guess that Flutter view of other platforms provide a method to notify first frame rendered

• Android
  public void addFirstFrameListener(FirstFrameListener listener)
• iOS
• (void)setFlutterViewDidRenderCallback:(void (^)(void))callback;

[JSUYA]

HI @bbrto21
I saw this problem and made a sample based on my ideas.
flutter-tizen/plugins#266 This PR was a way to register splash image in dart code.

In the evas_gl scenario, we can put a splash image in advance before setting the gl surface in evas_image.
After that, when the first frame of the flutter is drawn, we can set the gl surface to evas_image.

I made a sample based on this idea.
But I couldn't figure out when the first frame of the flutter was drawn.
So, when TizenRenderEventLoop's callback is called, I skipped the first call and set the gl surface when the second callback was called. (Of course, this is a just trick.)

I want to know when the first frame of the flutter is rendered. can you tell me about this?

[seungsoo47]

@JSUYA It's an good approach. I have a question for the splash image. If the splash image is always set before the first frame, can application developers change it later? I just wonder if it's possible because they might think that they want to set up a splash image for their company.

[swift-kim]

@seungsoo47 Am I understanding you correctly? A splash screen is configured by an app developer (in tizen-manifest.xml) when building their app.

[seungsoo47]

@JSUYA @swift-kim Oh~ I am sorry. It was my misunderstanding. Please ignore my question.

[JSUYA]

@swift-kim I do not know yet how to get the information of tizen-manifest.xml set in application from flutter-tizen.
um.. I think, we can add splash image path to FlutterDesktopEngineProperties. (maybe?)
anyway the basic idea of my opinion is to pre-set the image to evas_image before drawn flutter's first frame.

[swift-kim]

@JSUYA Oh, then you're not going to use Tizen's built-in splash screen feature? Hmm. That could be a good option. We might provide an API (such as FlutterApp.SetSplashImage()) in our embedding so that users can set splash image paths in their C++/C# code. A fun fact is that Android Flutter apps used to support a similar functionality through the provideSplashScreen interface but the Flutter team is now deprecating the API.

[bbrto21]

Recently, a patch that seem useful to solve this on the upstream side have been merged.

[swift-kim]

@bbrto21 I made an attempt by cherry-picking the patch but failed (the app window didn't show up after launch).

https://github.com/swift-kim/embedder/commits/next-frame-callback

The code defers calling TizenWindow::Show() until the engine is ready to draw a frame and explicitly schedules a frame after the engine is started. I'm not sure why this doesn't work. Am I doing right or did you mean something different?

[bbrto21]

@swift-kim Thanks for attempting. I took a look at what you tried but this only works properly when the FlutterRendererType is EGL. otherwise, the NextFrameCallback wasn't even called. I think we missed something. 😢