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Test Info: Warnings

<meta charset="utf-8">
<title>Test for Bug 1231622: Draw partial frames of downloading css background images</title>
<script src="/tests/SimpleTest/SimpleTest.js"></script>
<script src="/tests/SimpleTest/WindowSnapshot.js"></script>
<link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
<body onload="SimpleTest.waitForFocus(runTest)">
div {
width: 200px;
height: 200px;
background-size: 200px 200px; background-image: url(sendimagenevercomplete.sjs)
/* sendimagenevercomplete.sjs sends us a partial png file and keeps the
* connection open but sends no more data. This is enough data to draw at last
* a partial frame. We do this so that we can distinguish from drawing a
* partial frame after we've been told all data has arrived (what we do even
* without the pref layout.display_partial_background_images turned on), from
* drawing a partial frame while data is still arriving (what we want to do).
const gUtils = SpecialPowers.getDOMWindowUtils(window);
function checkPixel(r, x, y, red, green, blue, alpha) {
let canvas = snapshotRect(window, r);
let context = canvas.getContext('2d');
let image = context.getImageData(x, y, 1, 1);
if ([0] == red &&[1] == green &&[2] == blue &&[3] == alpha) {
return true;
return false;
async function runTest() {
await SpecialPowers.pushPrefEnv({'set': [['layout.display_partial_background_images', true]]});
let theDiv = document.createElement("div");
let r = theDiv.getBoundingClientRect();
// Give that some time to partially load.
for (let i = 0; i < 10; i++) {
await new Promise(resolve => requestAnimationFrame(resolve));
let correct = false;
while (!correct) {
// Check the middle pixel part way down the partial frame.
correct = checkPixel(r, 100, 25, 0, 0, 255, 255);
await new Promise(resolve => requestAnimationFrame(resolve));
ok(correct, "correct pixel value");