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<!DOCTYPE html>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="author" title="Manuel Rego Casasnovas" href="mailto:rego@igalia.com">
<link rel="help" href="https://drafts.csswg.org/cssom-view/#extension-to-the-element-interface">
<meta name="assert" content="This test checks that the scroll offsets behave as expected on fractional zoom situations.">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
.scrollable-area {
width: 100px;
height: 100px;
overflow: scroll;
}
.content {
width: 500px;
height: 500px;
background: lightgrey;
}
</style>
<div id="target" class="scrollable-area">
<div class="content"></div>
</div>
<script>
function runTest(zoom, x, y) {
// Scroll offsets might be snapped to device pixels for performance or
// rendering quality. Since scroll{Top,Left} round, we need to allow up to
// 1px of difference with the expected value.
const EPSILON = 1;
target.scrollTo(x, y);
test(() => {
assert_approx_equals(target.scrollLeft, x, EPSILON, `scrollLeft should be ${x}`);
}, `scrollLeft after scrollTo(${x}, ${y}) with 'zoom: ${zoom}'`);
test(() => {
assert_approx_equals(target.scrollTop, y, EPSILON, `scrollTop should be ${y}`);
}, `scrollTop after scrollTo(${x}, ${y}) with 'zoom: ${zoom}'`);
}
function runTests(zoom) {
target.style.zoom = zoom;
runTest(zoom, 0, 0);
runTest(zoom, 1, 2);
runTest(zoom, 13, 61);
runTest(zoom, 75, 100);
}
runTests(0.75);
runTests(0.9);
runTests(1);
runTests(1.13);
runTests(1.25);
runTests(1.5);
runTests(1.9);
runTests(2);
runTests(3.33);
</script>
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