How to ensure that webgl is loaded and can call SendMessage

Hello Thaina.

This task is not specific to WebGL, but rather it is a common situation when you wait for completion of multiple asynchronous operations in JavaScript. For example, it can be resolved like this:

Code (JavaScript):

1.   var dependencies = {
2.     'facebook_login' : true,
3.     'webgl_ready' : true,
4.   };
5.   function removeDependency(dependency) {
6.     if (dependencies[dependency])
7.       delete dependencies[dependency];
8.     if (!Object.keys(dependencies).length)
9.       SendMessage('Game','Ready');
10.   }

Your facebook login callback should therefore call removeDependency('facebook_login'), and your WebGL application should call removeDependency('webgl_ready') through jslib plugin from, let's say, Game.Start() (note that SendMessage will only work if the referenced game object exists and is active, therefore initialization of WebGL module itself is not sufficient, while execution of Game.Start guarantees that the Game object already exists). When both dependencies get removed, the Game.Ready() method will be executed. Also, if you want to ensure that initialization of all the game objects has been completed at the moment when Game.Ready() method is called, you might consider using setTimeout(function(){SendMessage('Game','Ready')},0) instead, so that it will be called the next frame after initialization.

 

As mentioned above, you have to ensure that the game object referenced in SendMessage has been already created. Game objects can be created dynamically and there is no way for Unity to know which object exactly you are waiting for, unless you are waiting for creation of all the static objects in the scene, but that is rather a specific usecase.

 

You might consider using a JavaScript plugin instead of the Application.ExternalCall. Not only because it will automatically solve you problem (you can get a return value from the executed JavaScript code), but also because ExternalCall is internally using JavaScript eval, which is a subject of security restrictions in specific environments (i.e. Chrome packaged app). Check out the StringReturnValueFunction function at the following link https://docs.unity3d.com/Manual/webgl-interactingwithbrowserscripting.html

Moreover, you are also able to synchronously return a value from a C# function to JavaScript. This is not as convenient as another direction of course, but still possible. The trick is that, unlike some other platforms, in WebGL the SendMessage is executed synchronously, so you can use a helper function and a JavaScript context variable to synchronously return a value back to JavaScript. Check out the following reply for a working example https://forum.unity3d.com/threads/super-fast-javascript-interaction-on-webgl.382734/#post-2573686