[Webkit-unassigned] [Bug 189397] New: Improvements to zooming helper functions

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=189397

            Bug ID: 189397
           Summary: Improvements to zooming helper functions
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: fred.wang at free.fr
                CC: simon.fraser at apple.com

We currently have at least three functions, with similar logic but different types of parameter. Maybe it would be possible to merge them into a single helper function. Some of them increment/decrement the value to workaround truncation and in bug 182230 Simon suggested to just floor/ceil after the division by zoomFactor. Not sure how that would impact accuracy.

RenderStyle.h:
inline int adjustForAbsoluteZoom(int value, const RenderStyle& style)
{
    double zoomFactor = style.effectiveZoom();
    if (zoomFactor == 1)
        return value;
    // Needed because computeLengthInt truncates (rather than rounds) when scaling up.
    if (zoomFactor > 1) {
        if (value < 0)
            value--;
        else 
            value++;
    }

    return roundForImpreciseConversion<int>(value / zoomFactor);
}

Element.cpp:
static double adjustForLocalZoom(LayoutUnit value, const RenderElement& renderer, double& zoomFactor)
{
    zoomFactor = localZoomForRenderer(renderer);
    if (zoomFactor == 1)
        return value.toDouble();
    return value.toDouble() / zoomFactor;
}

HTMLBodyElement.cpp
static int adjustForZoom(int value, const Frame& frame)
{
    double zoomFactor = frame.pageZoomFactor() * frame.frameScaleFactor();
    if (zoomFactor == 1)
        return value;
    // Needed because of truncation (rather than rounding) when scaling up.
    if (zoomFactor > 1)
        value++;
    return static_cast<int>(value / zoomFactor);
}

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