transferFromImageBitmap-null-offscreen.html

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This WPT test may be referenced by the following Test IDs:
- /imagebitmap-renderingcontext/transferFromImageBitmap-null-offscreen.html - WPT Dashboard Interop Dashboard

<!DOCTYPE html>

<meta charset="utf-8">

<title>Canvas's ImageBitmapRenderingContext test</title>

<script src="/resources/testharness.js"></script>

<script src="/resources/testharnessreport.js"></script>

<link rel="help" href="https://html.spec.whatwg.org/multipage/scripting.html#the-imagebitmap-rendering-context">

<script>

var width = 10;

var height = 10;

function testCanvas(bitmapCanvas, r, g, b, a)

    var myCanvas = document.createElement('canvas');

    myCanvas.width = width;

    myCanvas.height = height;

    var myCtx = myCanvas.getContext('2d');

    myCtx.drawImage(bitmapCanvas, 0, 0);

    var color = myCtx.getImageData(5, 5, 1, 1).data;

    assert_array_equals(color, [r, g, b, a]);

promise_test(function() {

    function testTransferFromImageBitmapNullability(greenImage, redImage) {

        var bitmapCanvas = new OffscreenCanvas(width,height);

        var bitmapCtx = bitmapCanvas.getContext('bitmaprenderer');

        bitmapCtx.transferFromImageBitmap(greenImage);

        // Make sure the bitmap renderer canvas is filled correctly.

        testCanvas(bitmapCanvas, 0, 255, 0, 255);

        // Test if passing null resets the bitmap renderer canvas.

        // Drawing the resetted canvas cannot change the destination canvas.

        bitmapCtx.transferFromImageBitmap(null);

        testCanvas(bitmapCanvas, 0, 0, 0, 0);

        // Test if we can redraw the bitmap canvas correctly after reset.

        bitmapCtx.transferFromImageBitmap(redImage);

        testCanvas(bitmapCanvas, 255, 0, 0, 255);

    var greenCanvas = document.createElement('canvas');

    greenCanvas.width = width;

    greenCanvas.height = height;

    var greenCtx = greenCanvas.getContext('2d');

    greenCtx.fillStyle = '#0f0';

    greenCtx.fillRect(0, 0, width, height);

    var redCanvas = document.createElement('canvas');

    redCanvas.width = width;

    redCanvas.height = height;

    var redCtx = redCanvas.getContext('2d');

    redCtx.fillStyle = '#f00';

    redCtx.fillRect(0, 0, width, height);

    return Promise.all([

        createImageBitmap(greenCanvas),

        createImageBitmap(redCanvas),

    ]).then(([greenImage, redImage]) => {

        testTransferFromImageBitmapNullability(greenImage, redImage);

});

},'Test that transferFromImageBitmap(null) discards the previously transferred image');

</script>