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<!DOCTYPE html>
<html class="reftest-wait">
<meta charset="utf-8">
<title>Test for Bug 1972885</title>
<style>
body {
margin: 0;
}
canvas {
/* Height would round up to 101px, but subpixel snaps to 100. */
margin-top: 1.6px;
width: 100px;
height: 100.5px;
}
</style>
<canvas id="canvas"></canvas>
<script>
function draw(canvas, width, height) {
const ctx = canvas.getContext('2d');
canvas.width = width;
canvas.height = height;
const imgData = ctx.createImageData(width, height);
const u32View = new Uint32Array(imgData.data.buffer);
u32View.fill(0xFFFFFFFF);
for (let y = 0; y < height; y += 2) {
for (let x = 0; x < width; x++) {
u32View[y * width + x] = 0xFF000000;
}
}
ctx.putImageData(imgData, 0, 0);
}
const ro = new ResizeObserver((entries) => {
for (const entry of entries) {
if (entry.target !== canvas) {
continue;
}
draw(
canvas,
entry.devicePixelContentBoxSize[0].inlineSize,
entry.devicePixelContentBoxSize[0].blockSize);
}
document.documentElement.removeAttribute("class");
});
// Get the properly subpixel snapped size through ResizeObserver.
ro.observe(canvas);
</script>
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