Bug 118495 – Page zoom/scale causes javascript auto scroll not work

• Status: UNCONFIRMED
• Component: Layout and Rendering

[Chen Zhixiang]

When set page zoom/scale factor to a value < 1,
then the JS code `element.content.scrollTop++` will be affected by this
And the page auto scroll will not work.

This problem exists in both newest Chrome 27 and Firefox 22.

Reason for this:
(1)In fact, zoom/scale operator should NOT apply to the point/position type, but only to the length type;
(2)Or maybe we can change the internal DOM layput impl's type from int to double?
(3)I had to say, the testcase expects a "continuous" style changing behavor, while discretized int-type values should always give a gap;


void Element::setScrollTop(int newTop)
{
    document()->updateLayoutIgnorePendingStylesheets();
    if (RenderBox* rend = renderBox())
        rend->setScrollTop(static_cast<int>(newTop * rend->style()->effectiveZoom())); //<---
}

[Chen Zhixiang]

Created attachment 206298 [details]
Testcase for this bug report

Load this page, and change the page zoom to <1 value, then the auto scroll will stop working