258967 2023-07-07 04:50:26 -0700 ShouldPaintUsingCompositeCopy feature is not stable with respect to layouts, resizes or similar 2023-07-07 04:52:13 -0700 1 1 1 Unclassified WebKit Compositing WebKit Local Build Unspecified Unspecified NEW InRadar P2 Normal --- 258964 1 kkinnunen webkit-unassigned simon.fraser webkit-bug-importer oldest_to_newest 1965521 0 kkinnunen 2023-07-07 04:50:26 -0700 Somehow on resizing and bringing up the print dialog, possibly just doing layout, the m_subpixelOffsetFromRenderer gets a small value such as ~0.18. This causes the optimization to be lost, because contentsBox "moves" away from the origo, even though in practice it does not. auto contents = contentsBox(); if (contents.location() != LayoutPoint(0, 0)) return false; E.g. repro case like: load page canvas gets the optimization resize canvas does not get the optimization reload canvas gets the optimization 1965522 1 webkit-bug-importer 2023-07-07 04:50:36 -0700 <rdar://problem/111902075> 1965523 2 466970 kkinnunen 2023-07-07 04:52:13 -0700 Created attachment 466970 proposal for LayoutTests/compositing/canvas/ resize/print this and add debug print to inspect whether the canvas is painted with Copy or SourceOver 466970 2023-07-07 04:52:13 -0700 2023-07-07 04:52:13 -0700 proposal for LayoutTests/compositing/canvas/ canvas-layer-transparent.html text/html 1815 kkinnunen PCFET0NUWVBFIGh0bWw+PGh0bWw+CjxoZWFkPgogICAgPHN0eWxlIHR5cGU9dGV4dC9jc3M+CiAg ICAgICAgZGl2IHsKICAgICAgICAgICAgdHJhbnNmb3JtOiB0cmFuc2xhdGVaKDFweCk7CiAgICAg ICAgfQogICAgICAgIGNhbnZhcyB7CiAgICAgICAgICAgIHRyYW5zZm9ybTp0cmFuc2xhdGVaKDFw eCk7CiAgICAgICAgfQogICAgPC9zdHlsZT4KPC9oZWFkPgo8Ym9keT4KPGRpdiBzdHlsZT0icG9z aXRpb246YWJzb2x1dGU7IHRyYW5zZm9ybS1vcmlnaW46IGNlbnRlciBjZW50ZXI7IHRyYW5zZm9y bTogc2NhbGVYKDAuODc1NTIxKSBzY2FsZVkoMC44NzU1MjEpOyBwZXJzcGVjdGl2ZS1vcmlnaW46 IGNlbnRlciBjZW50ZXI7IHRyYW5zZm9ybS1zdHlsZTogcHJlc2VydmUtM2Q7IHRvcDogLTY3LjIx ODc1cHg7IGxlZnQ6IC0xMTkuNXB4OyB3aWR0aDogMTkyMHB4OyBoZWlnaHQ6IDEwODBweDsiPgog ICAgPGRpdiBzdHlsZT0idG9wOiAwcHg7IGxlZnQ6IDBweDsgd2lkdGg6IDE5MjBweDsgaGVpZ2h0 OiAxMDgwcHg7IHBvc2l0aW9uOiBhYnNvbHV0ZTsgb3BhY2l0eTogMTsgdmlzaWJpbGl0eTogdmlz aWJsZTsgdHJhbnNmb3JtOiB0cmFuc2xhdGVaKDBweCk7IHRyYW5zZm9ybS1zdHlsZTogZmxhdDsi PgogICAgICAgIDxkaXYgaWQ9ImxheWVyODQiIHN0eWxlPSJwb2ludGVyLWV2ZW50czogbm9uZTsg dG9wOiAwcHg7IGxlZnQ6IDBweDsgd2lkdGg6IDE5MjBweDsgaGVpZ2h0OiAxMDgwcHg7IHBvc2l0 aW9uOiBhYnNvbHV0ZTsgb3BhY2l0eTogMTsgdmlzaWJpbGl0eTogdmlzaWJsZTsgdHJhbnNmb3Jt OiBtYXRyaXgoMSwgMCwgMCwgMSwgMCwgMCk7IHRyYW5zZm9ybS1zdHlsZTogZmxhdDsiPgogICAg ICAgICAgICA8ZGl2IGlkPSJsYXllcjg1IiBzdHlsZT0icG9pbnRlci1ldmVudHM6IG5vbmU7IHRv cDogMHB4OyBsZWZ0OiAwcHg7IHdpZHRoOiA0OTRweDsgaGVpZ2h0OiA0NnB4OyBwb3NpdGlvbjog YWJzb2x1dGU7IG9wYWNpdHk6IDE7IHZpc2liaWxpdHk6IHZpc2libGU7IHRyYW5zZm9ybTogbWF0 cml4KDEsIDAsIDAsIDEsIDY0Ni40ODk2NTMsIDcwLjM5NzY5OSk7IHRyYW5zZm9ybS1zdHlsZTog ZmxhdDsiPgogICAgICAgICAgICAgICAgPGRpdiBpZD0ibGF5ZXI4NiIgc3R5bGU9InBvaW50ZXIt ZXZlbnRzOiBub25lOyB0b3A6IDBweDsgbGVmdDogMHB4OyB3aWR0aDogNDk0cHg7IGhlaWdodDog NDZweDsgcG9zaXRpb246IGFic29sdXRlOyBvcGFjaXR5OiAxOyB2aXNpYmlsaXR5OiB2aXNpYmxl OyB0cmFuc2Zvcm06IG1hdHJpeCgxLCAwLCAwLCAxLCAzLjUxMDM0NywgMTQuNjAyMzAxKTsgdHJh bnNmb3JtLXN0eWxlOiBmbGF0OyI+CiAgICAgICAgICAgICAgICAgICAgPGNhbnZhcyB3aWR0aD0i NDk0IiBoZWlnaHQ9IjQ2IiBpZD0iYyIgc3R5bGU9InRvcDogMHB4OyBsZWZ0OiAwcHg7IHdpZHRo OiA0OTRweDsgaGVpZ2h0OiA0NnB4OyBwb3NpdGlvbjogYWJzb2x1dGU7IHRyYW5zZm9ybTogdHJh bnNsYXRlWigwcHgpOyI+CiAgICAgICAgICAgICAgICAgICAgPC9jYW52YXM+CiAgICAgICAgICAg ICAgICA8L2Rpdj4KICAgICAgICAgICAgPC9kaXY+CiAgICAgICAgPC9kaXY+CiAgICA8L2Rpdj4K PC9kaXY+CiAgICAKPHNjcmlwdD4KZnVuY3Rpb24gZigpIHsKICAgIHZhciBjdHggPSBjLmdldENv bnRleHQoJzJkJyk7CiAgICBjdHguZmlsbFN0eWxlID0gJ3JnYmEoMCwgMjU1LCAwLCAwLjUpJzsK ICAgIGN0eC5maWxsUmVjdCgwLCAwLCBjLndpZHRoLCBjLmhlaWdodCk7CiAgICByZXF1ZXN0QW5p bWF0aW9uRnJhbWUoZik7Cn0KZigpOwo8L3NjcmlwdD4KPC9ib2R5Pgo8L2h0bWw+