Bug 258967 – ShouldPaintUsingCompositeCopy feature is not stable with respect to layouts, resizes or similar

• Status: NEW
• Component: Compositing

[Kimmo Kinnunen]

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

[Radar WebKit Bug Importer]

<rdar://problem/111902075>

[Kimmo Kinnunen]

Created attachment 466970 [details]
proposal for LayoutTests/compositing/canvas/

resize/print this and add debug print to inspect whether the canvas is painted with Copy or SourceOver