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Question Changing javascript bindings - possible?

Discussion in 'Web' started by Marks4, Oct 5, 2020.

  1. Marks4

    Marks4

    Joined:
    Feb 25, 2018
    Posts:
    502
    So a quick example: When you call webcamdevice.name in Unity, the javascript function
    Code (javascript):
    1. _JS_WebCamVideo_GetDeviceName
    is called in webgl.framework.js, in the webgl build folder.

    Is there a way to somehow change the function that is called? I am well aware that I can simply overwrite the function _JS_WebCamVideo_GetDeviceName. But what if I don't want that? What if I want to bind the C# property to my own function? Because maybe there isn't a javascript binding for a certain property and I want to create one?

    I am aware that this is all possible with my own methods. But I'm talking about the built-in Unity methods/properties. Not something that I coded.

    How was the _JS_WebCamVideo_GetDeviceName added to the webgl.framework.js file? How does it connect to the webcamdevice.name property? The way we as users do it with our own methods/properties, is using .jslib files. But it seems Unity is doing something different here, because I can't find a .jslib that is doing this.

    @alexsuvorov @jukka_j @Marco-Trivellato @Schubkraft @MartinTilo @brendanduncan_u3d
     
    Last edited: Oct 5, 2020
    Marks4, Oct 5, 2020
    #1

  2. jukka_j

    jukka_j

    Unity Technologies

    Joined:
    May 4, 2018
    Posts:
    951
    The way that Unity does binding of C# property names to getter and setter functions in JavaScript is by supplying intermediate C++ code to do the wrapping, and the identical .jslib mechanism that user code is using. There is no direct "language" mechanism that would route C# properties to JS function.

    Just for build system reasons, the Unity-provided .jslib files are not named with a .jslib suffix, but have a regular .js suffix. So the file WebCam.js with that function is like a "WebCam.jslib" in user project.

    Basically the machinery that is in play here is twofold:
    - "Standard" C#-to-C/C++ "P/Invoke" marshalling is used to call back and forth between C# and C/C++.
    - The .jslib files are an Emscripten compiler provided mechanism to enable implementing JavaScript functions that take place in C/C++ linkage. In Unity C# context, this means C# can "P/Invoke out" to a JS function in a .jslib file.

    https://answers.unity.com/questions/1742028/use-c-script-to-call-javascript-functionmethod.html contains a good thread with example code.
     
    jukka_j, Oct 5, 2020
    #2

  3. Marks4

    Marks4

    Joined:
    Feb 25, 2018
    Posts:
    502
    Hi @jukka_j , thanks for the reply. Yes, I know how to do it with my own methods and properties. But what about native Unity methods and properties? Can I do it with those, somehow? So I call webcamdevice.name on C#. And I want to trigger my own javascript function when I do that, instead of _JS_WebCamVideo_GetDeviceName. Let's call it _JS_WebCamVideo_GetDeviceName_Custom.

    To reiterate, I don't want the _JS_WebCamVideo_GetDeviceName javascript method to be called. I want my own js method to be called.

    Is it possible, for me, as a user to do that?
     
    Marks4, Oct 5, 2020
    #3

  4. jukka_j

    jukka_j

    Unity Technologies

    Joined:
    May 4, 2018
    Posts:
    951
    Unfortunately it is not possible to override built-in Unity C# API provided properties in user code that I know of.

    If you have custom C# code with properties, you can implement getter and setter functions for them that P/Invoke over out to JavaScript. That can make it look transparent for the user like they would be accessing only a C# surface.
     
    jukka_j, Oct 5, 2020
    #4
    Marks4 likes this.

  5. Marks4

    Marks4

    Joined:
    Feb 25, 2018
    Posts:
    502
    I see, oh well. That's unfortunate. Thanks jukka!
     
    Marks4, Oct 5, 2020
    #5