C++ FrameMetrics::GetParentResolution方法代码示例

void
APZCCallbackHelper::UpdateRootFrame(nsIDOMWindowUtils* aUtils,
                                    FrameMetrics& aMetrics)
{
    // Precondition checks
    MOZ_ASSERT(aUtils);
    MOZ_ASSERT(aMetrics.GetUseDisplayPortMargins());
    if (aMetrics.GetScrollId() == FrameMetrics::NULL_SCROLL_ID) {
        return;
    }

    // Set the scroll port size, which determines the scroll range. For example if
    // a 500-pixel document is shown in a 100-pixel frame, the scroll port length would
    // be 100, and gecko would limit the maximum scroll offset to 400 (so as to prevent
    // overscroll). Note that if the content here was zoomed to 2x, the document would
    // be 1000 pixels long but the frame would still be 100 pixels, and so the maximum
    // scroll range would be 900. Therefore this calculation depends on the zoom applied
    // to the content relative to the container.
    CSSSize scrollPort = aMetrics.CalculateCompositedSizeInCssPixels();
    aUtils->SetScrollPositionClampingScrollPortSize(scrollPort.width, scrollPort.height);

    // Scroll the window to the desired spot
    nsIScrollableFrame* sf = nsLayoutUtils::FindScrollableFrameFor(aMetrics.GetScrollId());
    bool scrollUpdated = false;
    CSSPoint actualScrollOffset = ScrollFrameTo(sf, aMetrics.GetScrollOffset(), scrollUpdated);

    if (scrollUpdated) {
        // Correct the display port due to the difference between mScrollOffset and the
        // actual scroll offset.
        AdjustDisplayPortForScrollDelta(aMetrics, actualScrollOffset);
    } else {
        // For whatever reason we couldn't update the scroll offset on the scroll frame,
        // which means the data APZ used for its displayport calculation is stale. Fall
        // back to a sane default behaviour. Note that we don't tile-align the recentered
        // displayport because tile-alignment depends on the scroll position, and the
        // scroll position here is out of our control. See bug 966507 comment 21 for a
        // more detailed explanation.
        RecenterDisplayPort(aMetrics);
    }

    aMetrics.SetScrollOffset(actualScrollOffset);

    // The mZoom variable on the frame metrics stores the CSS-to-screen scale for this
    // frame. This scale includes all of the (cumulative) resolutions set on the presShells
    // from the root down to this frame. However, when setting the resolution, we only
    // want the piece of the resolution that corresponds to this presShell, rather than
    // all of the cumulative stuff, so we need to divide out the parent resolutions.
    // Finally, we multiply by a ScreenToLayerScale of 1.0f because the goal here is to
    // take the async zoom calculated by the APZC and tell gecko about it (turning it into
    // a "sync" zoom) which will update the resolution at which the layer is painted.
    ParentLayerToLayerScale presShellResolution =
        aMetrics.GetZoom()
        / aMetrics.mDevPixelsPerCSSPixel
        / aMetrics.GetParentResolution()
        * ScreenToLayerScale(1.0f);
    aUtils->SetResolution(presShellResolution.scale, presShellResolution.scale);

    // Finally, we set the displayport.
    nsCOMPtr<nsIContent> content = nsLayoutUtils::FindContentFor(aMetrics.GetScrollId());
    if (!content) {
        return;
    }
    nsCOMPtr<nsIDOMElement> element = do_QueryInterface(content);
    if (!element) {
        return;
    }

    gfx::IntSize alignment = gfxPrefs::LayersTilesEnabled()
        ? gfx::IntSize(gfxPrefs::LayersTileWidth(), gfxPrefs::LayersTileHeight()) :
          gfx::IntSize(0, 0);
    LayerMargin margins = aMetrics.GetDisplayPortMargins();
    aUtils->SetDisplayPortMarginsForElement(margins.left,
                                            margins.top,
                                            margins.right,
                                            margins.bottom,
                                            alignment.width,
                                            alignment.height,
                                            element, 0);
    CSSRect baseCSS = aMetrics.CalculateCompositedRectInCssPixels();
    nsRect base(baseCSS.x * nsPresContext::AppUnitsPerCSSPixel(),
                baseCSS.y * nsPresContext::AppUnitsPerCSSPixel(),
                baseCSS.width * nsPresContext::AppUnitsPerCSSPixel(),
                baseCSS.height * nsPresContext::AppUnitsPerCSSPixel());
    nsLayoutUtils::SetDisplayPortBaseIfNotSet(content, base);
}