test_img_picture_preload.html

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<!DOCTYPE HTML>

<html>

<!--

https://bugzilla.mozilla.org/show_bug.cgi?id=1067345

-->

<head>

  <title>Test for Bug 1067345</title>

  <script src="/tests/SimpleTest/SimpleTest.js"></script>

  <link rel="stylesheet" href="/tests/SimpleTest/test.css">

</head>

<body>

  <script>

    // Ensure srcset/picture are enabled, re-run the test at different DPI

    // levels to ensure preload step does the right responsive image selection

    SimpleTest.waitForExplicitFinish();

    var testDPIs = ["1.0", "0.5", "2.0", "1.5"];

    var iframe = document.createElement("iframe");

    // These accessed by child frame

    var currentDPI;

    document.body.appendChild(iframe);

    // Reset the sjs helper so repeat runs work

    resetRequests();

    setTimeout(nextTest, 0);

    function resetRequests() {

      // Ask the SJS to reset requests

      var request = new XMLHttpRequest();

      request.open("GET", "./file_img_picture_preload.sjs?reset", false);

      request.send(null);

      is(request.status, 200, "Sending reset to helper should succeed");

      // Script responds with pre-reset request count

      var previousRequests = +request.responseText;

      return previousRequests;

    // Called when iframe is finished

    function childTestFinished(requestsMade) {

      setTimeout(function() {

        // Reset sjs, ensure no new requests appeared after test finished

        var requestsCleared = resetRequests();

        is(requestsCleared, requestsMade,

           "Should not have recorded new requests after test iteration completed");

        setTimeout(nextTest, 0);

      }, 0);

    function nextTest() {

      // Re-run test for each DPI level

      if (!testDPIs.length) {

        SimpleTest.finish();

        return;

      currentDPI = testDPIs.pop();

      info("Starting test for DPI: " + currentDPI);

      // To avoid spurious image loads being reported when the resolution changes,

      // load an intermediate iframe.

      iframe.src = "about:blank";

      iframe.addEventListener("load", async function() {

        await SpecialPowers.pushPrefEnv({"set": [ [ "layout.css.devPixelsPerPx", currentDPI ]] });

        // Make sure we trigger a layout flush so that the frame is sized

        // appropriately after the DPI changes.

        iframe.getBoundingClientRect();

        // Clear image cache for next run (we don't try to validate cached items

        // in preload).

        SpecialPowers.Cc["@mozilla.org/image/tools;1"]

                     .getService(SpecialPowers.Ci.imgITools)

                     .getImgCacheForDocument(iframe.contentDocument)

                     .clearCache(false);

        iframe.src = "./file_img_picture_preload.html?" + currentDPI;

      }, {once: true});

  </script>

</body>

</html>