Bug 189397 - Improvements to zooming helper functions
Summary: Improvements to zooming helper functions
Status: NEW
Alias: None
Product: WebKit
Classification: Unclassified
Component: WebCore Misc. (show other bugs)
Version: WebKit Nightly Build
Hardware: Unspecified Unspecified
: P2 Normal
Assignee: Nobody
Depends on:
Reported: 2018-09-06 23:30 PDT by Frédéric Wang (:fredw)
Modified: 2018-09-06 23:30 PDT (History)
1 user (show)

See Also:


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Description Frédéric Wang (:fredw) 2018-09-06 23:30:05 PDT
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.

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)

    return roundForImpreciseConversion<int>(value / zoomFactor);

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

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)
    return static_cast<int>(value / zoomFactor);