зеркало из https://github.com/mozilla/gecko-dev.git
Bug 1518584 - Update out-of-date comments in FrameMetrics.h. r=kats
Differential Revision: https://phabricator.services.mozilla.com/D15970 --HG-- extra : moz-landing-system : lando
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@ -45,10 +45,21 @@ struct ScrollUpdateInfo {
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};
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/**
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* The viewport and displayport metrics for the painted frame at the
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* time of a layer-tree transaction. These metrics are especially
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* useful for shadow layers, because the metrics values are updated
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* atomically with new pixels.
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* Metrics about a scroll frame that are sent to the compositor and used
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* by APZ.
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*
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* This is used for two main purposes:
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*
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* (1) Sending information about a scroll frame to the compositor and APZ
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* as part of a layers or WebRender transaction.
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* (2) Storing information about a scroll frame in APZ that persists
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* between transactions.
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*
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* TODO: Separate these two uses into two distinct structures.
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*
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* A related class, RepaintRequest, is used for sending information about a
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* scroll frame back from the compositor to the main thread when requesting
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* a repaint of the scroll frame's contents.
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*/
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struct FrameMetrics {
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friend struct IPC::ParamTraits<mozilla::layers::FrameMetrics>;
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@ -492,46 +503,41 @@ struct FrameMetrics {
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const CSSRect& aVisualViewport, CSSRect& aLayoutViewport);
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private:
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// A unique ID assigned to each scrollable frame.
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// A ID assigned to each scrollable frame, unique within each LayersId..
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ViewID mScrollId;
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// The pres-shell resolution that has been induced on the document containing
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// this scroll frame as a result of zooming this scroll frame (whether via
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// user action, or choosing an initial zoom level on page load). This can
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// only be different from 1.0 for frames that are zoomable, which currently
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// is just the root content document's root scroll frame (mIsRoot = true).
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// is just the root content document's root scroll frame
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// (mIsRootContent = true).
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// This is a plain float rather than a ScaleFactor because in and of itself
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// it does not convert between any coordinate spaces for which we have names.
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float mPresShellResolution;
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// This is the area within the widget that we're compositing to. It is in the
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// same coordinate space as the reference frame for the scrolled frame.
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// layer coordinates of the scrollable content's parent layer.
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//
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// This is useful because, on mobile, the viewport and composition dimensions
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// are not always the same. In this case, we calculate the displayport using
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// an area bigger than the region we're compositing to. If we used the
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// viewport dimensions to calculate the displayport, we'd run into situations
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// where we're prerendering the wrong regions and the content may be clipped,
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// or too much of it prerendered. If the composition dimensions are the same
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// as the viewport dimensions, there is no need for this and we can just use
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// the viewport instead.
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// The size of the composition bounds corresponds to the size of the scroll
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// frame's scroll port (but in a coordinate system where the size does not
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// change during zooming).
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//
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// This value is valid for nested scrollable layers as well, and is still
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// relative to the layer tree origin. This value is provided by Gecko at
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// layout/paint time.
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// The origin of the composition bounds is relative to the layer tree origin.
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// Unlike the scroll port's origin, it does not change during scrolling.
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//
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// This value is provided by Gecko at layout/paint time.
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ParentLayerRect mCompositionBounds;
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// The area of a frame's contents that has been painted, relative to
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// mCompositionBounds.
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// The area of a scroll frame's contents that has been painted, relative to
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// mScrollOffset.
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//
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// Note that this is structured in such a way that it doesn't depend on the
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// method layout uses to scroll content.
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// Should not be larger than GetExpandedScrollableRect().
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//
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// May be larger or smaller than |mScrollableRect|.
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//
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// To pre-render a margin of 100 CSS pixels around the window,
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// To pre-render a margin of 100 CSS pixels around the scroll port,
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// { x = -100, y = - 100,
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// width = window.innerWidth + 200, height = window.innerHeight + 200 }
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// width = scrollPort.width + 200, height = scrollPort.height + 200 }
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// where scrollPort = CalculateCompositedSizeInCssPixels().
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CSSRect mDisplayPort;
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// If non-empty, the area of a frame's contents that is considered critical
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@ -553,10 +559,8 @@ struct FrameMetrics {
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// the scrollable range to 0.
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//
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// This is in the same coordinate space as |mScrollOffset|, but a different
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// coordinate space than |mViewport| and |mDisplayPort|. Note also that this
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// coordinate system is understood by window.scrollTo().
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//
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// This is valid on any layer unless it has no content.
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// coordinate space than |mDisplayPort|. Note also that this coordinate
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// system is understood by window.scrollTo().
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CSSRect mScrollableRect;
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// The cumulative resolution that the current frame has been painted at.
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@ -564,41 +568,33 @@ struct FrameMetrics {
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// containing this scroll frame and its ancestors, and any css-driven
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// resolution. This information is provided by Gecko at layout/paint time.
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// Note that this is allowed to have different x- and y-scales, but only
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// for subframes (mIsRoot = false). (The same applies to other scales that
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// "inherit" the 2D-ness of this one, such as mZoom.)
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// for subframes (mIsRootContent = false). (The same applies to other scales
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// that "inherit" the 2D-ness of this one, such as mZoom.)
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LayoutDeviceToLayerScale2D mCumulativeResolution;
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// New fields from now on should be made private and old fields should
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// be refactored to be private.
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// The conversion factor between CSS pixels and device pixels for this frame.
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// This can vary based on a variety of things, such as reflowing-zoom. The
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// conversion factor for device pixels to layers pixels is just the
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// resolution.
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// This can vary based on a variety of things, such as reflowing-zoom.
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CSSToLayoutDeviceScale mDevPixelsPerCSSPixel;
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// The position of the top-left of the CSS viewport, relative to the document
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// (or the document relative to the viewport, if that helps understand it).
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// The position of the top-left of the scroll frame's scroll port, relative
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// to the scrollable content's origin.
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//
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// Thus it is relative to the document. It is in the same coordinate space as
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// |mScrollableRect|, but a different coordinate space than |mViewport| and
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// |mDisplayPort|.
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// This is in the same coordinate space as |mScrollableRect|, but a different
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// coordinate space than |mDisplayPort|.
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//
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// It is required that the rect:
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// { x = mScrollOffset.x, y = mScrollOffset.y,
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// width = mCompositionBounds.x / mResolution.scale,
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// height = mCompositionBounds.y / mResolution.scale }
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// Be within |mScrollableRect|.
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//
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// This is valid for any layer, but is always relative to this frame and
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// not any parents, regardless of parent transforms.
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// width = scrollPort.width,
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// height = scrollPort.height }
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// (where scrollPort = CalculateCompositedSizeInCssPixels())
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// be within |mScrollableRect|.
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CSSPoint mScrollOffset;
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// The base scroll offset to use for calculating a relative update to a
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// scroll offset.
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CSSPoint mBaseScrollOffset;
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// The "user zoom". Content is painted by gecko at mResolution *
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// The "user zoom". Content is painted by gecko at mCumulativeResolution *
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// mDevPixelsPerCSSPixel, but will be drawn to the screen at mZoom. In the
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// steady state, the two will be the same, but during an async zoom action the
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// two may diverge. This information is initialized in Gecko but updated in
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@ -622,22 +618,28 @@ struct FrameMetrics {
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uint32_t mPresShellId;
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// The CSS viewport, which is the dimensions we're using to constrain the
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// <html> element of this frame, relative to the top-left of the layer. Note
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// that its offset is structured in such a way that it doesn't depend on the
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// method layout uses to scroll content.
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// For a root scroll frame (RSF), the document's layout viewport
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// (sometimes called "CSS viewport" in older code).
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//
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// This is mainly useful on the root layer, however nested iframes can have
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// their own viewport, which will just be the size of the window of the
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// iframe. For layers that don't correspond to a document, this metric is
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// meaningless and invalid.
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// Its size is the dimensions we're using to constrain the <html> element
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// of the document (i.e. the initial containing block (ICB) size).
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//
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// Its origin is the RSF's layout scroll position, i.e. the scroll position
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// exposed to web content via window.scrollX/Y.
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//
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// Note that only the root content document's RSF has a layout viewport
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// that's distinct from the visual viewport. For an iframe RSF, the two
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// are the same.
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//
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// For a scroll frame that is not an RSF, this metric is meaningless and
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// invalid.
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CSSRect mViewport;
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// The extra resolution at which content in this scroll frame is drawn beyond
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// that necessary to draw one Layer pixel per Screen pixel.
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ScreenToLayerScale2D mExtraResolution;
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// The time at which the APZC last requested a repaint for this scrollframe.
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// The time at which the APZC last requested a repaint for this scroll frame.
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TimeStamp mPaintRequestTime;
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// Whether mScrollOffset was updated by something other than the APZ code, and
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@ -659,7 +661,10 @@ struct FrameMetrics {
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// otherwise use the display port rect.
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bool mUseDisplayPortMargins : 1;
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// Whether or not this frame has a "scroll info layer" to capture events.
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// True if this scroll frame is a scroll info layer. A scroll info layer is
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// not layerized and its content cannot be truly async-scrolled, but its
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// metrics are still sent to and updated by the compositor, with the updates
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// being reflected on the next paint rather than the next composite.
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bool mIsScrollInfoLayer : 1;
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// WARNING!!!!
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@ -673,7 +678,7 @@ struct FrameMetrics {
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// (as needed):
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// FrameMetrics::operator ==
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// AsyncPanZoomController::NotifyLayersUpdated
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// The ParamTraits specialization in GfxMessageUtils.h
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// The ParamTraits specialization in LayersMessageUtils.h
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//
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// Please add new fields above this comment.
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@ -782,11 +787,12 @@ struct LayerClip {
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typedef Maybe<LayerClip> MaybeLayerClip; // for passing over IPDL
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/**
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* Metadata about a scroll frame that's stored in the layer tree for use by
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* the compositor (including APZ). This includes the scroll frame's
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* FrameMetrics, as well as other metadata. We don't put the other metadata into
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* FrameMetrics to avoid FrameMetrics becoming too bloated (as a FrameMetrics is
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* e.g. sent over IPC for every repaint request for every active scroll frame).
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* Metadata about a scroll frame that's sent to the compositor during a layers
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* or WebRender transaction, and also stored by APZ between transactions.
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* This includes the scroll frame's FrameMetrics, as well as other metadata.
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* We don't put the other metadata into FrameMetrics to avoid FrameMetrics
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* becoming too bloated (as a FrameMetrics is e.g. stored in memory shared
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* with the content process).
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*/
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struct ScrollMetadata {
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friend struct IPC::ParamTraits<mozilla::layers::ScrollMetadata>;
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@ -1007,8 +1013,7 @@ struct ScrollMetadata {
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// updated to include them (as needed):
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// 1. ScrollMetadata::operator ==
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// 2. AsyncPanZoomController::NotifyLayersUpdated
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// 3. The ParamTraits specialization in GfxMessageUtils.h and/or
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// LayersMessageUtils.h
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// 3. The ParamTraits specialization in LayersMessageUtils.h
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//
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// Please add new fields above this comment.
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};
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