The picture cache code selects an appropriate tile size to use by considering the size of the content rectangle [1]. We only ever want to create small sized tiles for real scrollbars. When we decide to create a picture for a scrollbar, it's based on the presence of a tag in the primitive cluster flags [2]. Instead of basing this decision on size, we could propagate those cluster flags when creating the `TileCacheInstance`. Then, we could only select a scrollbar tile size if this picture has been tagged as a scrollbar. [1] https://searchfox.org/mozilla-central/rev/0678172d5b5c681061b904c776b668489e3355b0/gfx/wr/webrender/src/picture.rs#1678 [2] https://searchfox.org/mozilla-central/rev/0678172d5b5c681061b904c776b668489e3355b0/gfx/wr/webrender/src/picture.rs#1678
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The picture cache code selects an appropriate tile size to use by considering the size of the content rectangle [1]. We only ever want to create small sized tiles for real scrollbars. When we decide to create a picture for a scrollbar, it's based on the presence of a tag in the primitive cluster flags [2]. Instead of basing this decision on size, we could propagate those cluster flags when creating the `TileCacheInstance`. Then, we could only select a scrollbar tile size if this picture has been tagged as a scrollbar. [1] https://searchfox.org/mozilla-central/rev/0678172d5b5c681061b904c776b668489e3355b0/gfx/wr/webrender/src/picture.rs#1678 [2] https://searchfox.org/mozilla-central/rev/0678172d5b5c681061b904c776b668489e3355b0/gfx/wr/webrender_api/src/display_item.rs#43