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Diffstat (limited to 'layout/style/test/test_viewport_scrollbar_causing_reflow.html')
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diff --git a/layout/style/test/test_viewport_scrollbar_causing_reflow.html b/layout/style/test/test_viewport_scrollbar_causing_reflow.html new file mode 100644 index 0000000000..ced14f352a --- /dev/null +++ b/layout/style/test/test_viewport_scrollbar_causing_reflow.html @@ -0,0 +1,130 @@ +<!DOCTYPE HTML> +<html> +<!-- +https://bugzilla.mozilla.org/show_bug.cgi?id=1367568 +--> +<head> + <meta charset="utf-8"> + <title>Test for Bug 1367568</title> + <script src="/tests/SimpleTest/SimpleTest.js"></script> + <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/> +</head> +<body> +<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=">Mozilla Bug 1367568</a> +<div id="content"> + <!-- Some fixed-width divs that we shouldn't have to reflow when the viewport + changes. More than 5 so that our leeway for scrollbar parts doesn't + accidentally cause the test to pass --> + <div style="width: 100px">fixed-width <div>(child)</div></div> + <div style="width: 100px">fixed-width <div>(child)</div></div> + <div style="width: 100px">fixed-width <div>(child)</div></div> + <div style="width: 100px">fixed-width <div>(child)</div></div> + <div style="width: 100px">fixed-width <div>(child)</div></div> + <div style="width: 100px">fixed-width <div>(child)</div></div> + <div style="position: absolute; width: 150px"> + abs-fixed-width + <div>(child)</div> + </div> +</div> +<pre id="test"> +<script> +"use strict"; + +/** Test for Bug 1367568 **/ + +/** + * This test verifies that "overflow" changes on the <body> don't cause + * an unnecessarily large amount of reflow. + */ + +// Vars used in setStyleAndMeasure that we really only have to look up once: +const gUtils = SpecialPowers.getDOMWindowUtils(window); + +function setStyleAndMeasure(initialStyle, finalStyle) { + is(document.body.style.length, 0, + "Bug in test - body should start with empty style"); + let unusedVal = document.body.offsetHeight; // flush layout + let constructCount = gUtils.framesConstructed; + + document.body.style = initialStyle; + unusedVal = document.body.offsetHeight; // flush layout + let reflowCountBeforeTweak = gUtils.framesReflowed; + + document.body.style = finalStyle; + unusedVal = document.body.offsetHeight; // flush layout + let reflowCountAfterTweak = gUtils.framesReflowed; + + // Clean up: + document.body.style = ""; + + is(gUtils.framesConstructed, constructCount, + "Style tweak shouldn't have triggered frame construction"); + + // ...and return the delta: + return reflowCountAfterTweak - reflowCountBeforeTweak; +} + +function main() { + // First, we sanity-check that our measurement make sense -- if we leave + // styles unchanged, we should measure no frames being reflowed: + let count = setStyleAndMeasure("width: 50px; height: 80px", + "width: 50px; height: 80px"); + is(count, 0, + "Shouldn't reflow anything when we leave 'width' & 'height' unchanged"); + + // Now: see how many frames are reflowed when the "width" & "height" change. + // We'll use this as the reference when measuring reflow counts for various + // changes to "overflow" below. + count = setStyleAndMeasure("width: 50px; height: 80px", + "width: 90px; height: 60px"); + ok(count > 0, + "Should reflow some frames when 'width' & 'height' change"); + + const scrollbarsHaveButtons = navigator.platform.includes("Win"); + // This is to allow for reflowing scrollbar parts themselves. + const scrollbarReflows = scrollbarsHaveButtons ? 5 : 2; + // Expected maximum number of frames reflowed for "overflow" changes + const expectedMax = count + scrollbarReflows; + + // Shared ending for messages in all ok() checks below: + const messageSuffix = + " shouldn't be greater than count for tweaking width/height on body (" + + expectedMax + ")"; + + // OK, here is where the relevant tests actually begin!! + // See how many frames we reflow for various tweaks to "overflow" on + // the body -- we expect the count to be no larger than |expectedMax|. + count = setStyleAndMeasure("", "overflow: scroll"); + ok(count <= expectedMax, + "Reflow count when setting 'overflow: scroll' on body (" + count + ")" + + messageSuffix); + + count = setStyleAndMeasure("", "overflow: hidden"); + ok(count <= expectedMax, + "Reflow count when setting 'overflow: hidden' on body (" + count + ")" + + messageSuffix); + + // Test removal of "overflow: scroll": + count = setStyleAndMeasure("overflow: scroll", ""); + ok(count <= expectedMax, + "Reflow count when removing 'overflow: scroll' from body (" + count + ")" + + messageSuffix); + + count = setStyleAndMeasure("overflow: hidden", ""); + ok(count <= expectedMax, + "Reflow count when removing 'overflow: hidden' from body (" + count + ")" + + messageSuffix); + + // Test change between two non-'visible' overflow values: + count = setStyleAndMeasure("overflow: scroll", "overflow: hidden"); + ok(count <= expectedMax, + "Reflow count when changing 'overflow' on body (" + count + ")" + + messageSuffix); +} + +main(); + +</script> +</pre> +</body> +</html> |