ClassCastException when creating default context in JS

Question

ClassCastException when creating default context in JS

Closed this issue 3 years ago · 2 comments

I've made clean Kotlin/JS project, add dependency


kotlin {
    js(IR) {
        binaries.executable()
        browser {
            commonWebpackConfig {
                cssSupport.enabled = true
            }
        }
    }

    dependencies {
        implementation("de.fabmax.kool:kool-core-js:0.8.0")
    }
}

Build and run, got ClassCastException in console:

"ClassCastException
    at THROW_CCE (webpack-internal:///./kotlin/untitled.js:21774:11)
    at new JsContext (webpack-internal:///./kotlin/untitled.js:89775:68)
    at JsImpl.createContext_u6767_k$ (webpack-internal:///./kotlin/untitled.js:86481:20)
    at createContext (webpack-internal:///./kotlin/untitled.js:86443:33)
    at createDefaultContext (webpack-internal:///./kotlin/untitled.js:86440:12)
    at main (webpack-internal:///./kotlin/untitled.js:95226:15)
    at Object.eval (webpack-internal:///./kotlin/untitled.js:95613:3)
    at eval (webpack-internal:///./kotlin/untitled.js:5:35)
    at eval (webpack-internal:///./kotlin/untitled.js:8:2)
    at Object../kotlin/untitled.js (http://localhost:8080/untitled.js:505:1)"

my versions:
kotlin: 1.6.10
webpack: 5.57.1

Answer 1 · 2022-02-11T17:09:13.000Z

Hmm I've never seen this error and it's a bit difficult to see where this happens without the correct line numbers.

As a wild guess I could imagine that the error happens on getting the canvas element, which is casted to an HTMLCanvasElement does your html contain a canvas element with id glCanvas (like in the kool-demo index.html)?

Answer 2 · 2022-02-11T21:32:12.000Z

Yes, index.html is just with <script>, and nothing more. WIth such index.html it looks like working great:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>Kotlin + OpenGL = KOOL</title>
    <style>
        body {
            background-color: black;
            border: 0;
            padding: 0;
            margin: 0;
        }
        canvas {
            width: 100vw;
            height: 100vh;
            display: block;
        }
    </style>
</head>
<body>
    <!-- Hidden div is needed to get the physical screen resolution, i.e. how many pixels fit into 1 inch -->
    <!-- Apparently this always results in 96 dpi anyway... :/ -->
    <div id="dpiMeasure" style="height: 1in; width: 1in; position: fixed; left: 100%; top: 100%;"></div>

    <!-- tabindex is required to make canvas focusable, needed to get per-canvas key events -->
    <canvas id="glCanvas" tabindex="1">
        Your browser doesn't appear to support the
        <code>&lt;canvas&gt;</code> element.
    </canvas>

    <script src="untitled.js"></script>

</body>
</html>

But. looks like need some dumb proof error handling.