sprite-sampling-clamp-2.html

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<head>

<meta charset="utf-8">

<title>Bug 2068996: a repeating sprite sheet must sample the cell it is positioned on</title>

<style>

html, body { margin: 0; background: white; }

/* The strip's middle cell is green with a black square in one corner, between

   two red cells. The square is what makes a shift visible: measuring the sampled

   part against the wrong extent lands it in the middle of the cell, where the

   shader's clamp holds sampling on flat green and the square never appears.

   A positive background-position under background-repeat picks the same cell as

   a negative one a whole period away, but reaches WebRender differently: the

   item's rect starts on the first tile, one period to the left, and is trimmed

   to the fill area, so it is narrower than a single repetition. The sampled

   part of the image has to be measured against the repetition, not against

   that rect. */

div {

  width: 16px;

  height: 16px;

  background-image: url(sprite-sampling-strip.png);

  background-size: 48px 16px;

  background-position-x: 32px;

  background-repeat: repeat;

</style>

</head>

<body><div></div></body>

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