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- // Copyright 2019 The Chromium Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style license that can be
- // found in the LICENSE file.
- #ifndef CC_INPUT_SCROLLBAR_CONTROLLER_H_
- #define CC_INPUT_SCROLLBAR_CONTROLLER_H_
- #include <memory>
- #include "base/cancelable_callback.h"
- #include "base/gtest_prod_util.h"
- #include "base/memory/raw_ptr.h"
- #include "base/time/time.h"
- #include "cc/cc_export.h"
- #include "cc/input/input_handler.h"
- #include "cc/input/scrollbar.h"
- #include "cc/layers/layer_impl.h"
- #include "cc/layers/painted_scrollbar_layer_impl.h"
- #include "third_party/abseil-cpp/absl/types/optional.h"
- // High level documentation:
- // https://source.chromium.org/chromium/chromium/src/+/main:cc/input/README.md
- // Click scrolling.
- // - A click is considered as a kMouseDown and a kMouseUp in quick succession.
- // Every click on a composited non-custom arrow leads to 3 GestureEvents in
- // total.
- // - GSB and GSU on get queued in the CTEQ on mousedown and a GSE on mouseup.
- // - The delta scrolled is constant at 40px (scaled by the device_scale_factor)
- // for scrollbar arrows and a function of the viewport length in the case of
- // track autoscroll.
- // Thumb dragging.
- // - The sequence of events in the CTEQ would be something like GSB, GSU, GSU,
- // GSU..., GSE
- // - On every pointermove, the scroll delta is determined is as current pointer
- // position - the point at which we got the initial mousedown.
- // - The delta is then scaled by the scroller to scrollbar ratio so that
- // dragging the thumb moves the scroller proportionately.
- // - This ratio is calculated as:
- // (scroll_layer_length - viewport_length) /
- // (scrollbar_track_length - scrollbar_thumb_length)
- // - On pointerup, the GSE clears state as mentioned above.
- // VSync aligned autoscroll.
- // - Autoscroll is implemented as a "scroll animation" which has a linear timing
- // function (see cc::LinearTimingFunction) and a curve with a constant velocity.
- // - The main thread does autoscrolling by pumping events at 50ms interval. To
- // have a similar kind of behaviour on the compositor thread, the autoscroll
- // velocity is set to 800px per second for scrollbar arrows.
- // - For track autoscrolling however, the velocity is a function of the viewport
- // length.
- // - Based on this velocity, an autoscroll curve is created.
- // - An autoscroll animation is set up. (via
- // LayerTreeHostImpl::ScrollAnimationCreateInternal) on the the known
- // scroll_node and the scroller starts animation when the pointer is held.
- // Nuances:
- // Thumb snapping.
- // - During a thumb drag, if a pointer moves too far away from the scrollbar
- // track, the thumb is supposed to snap back to it original place (i.e to the
- // point before the thumb drag started).
- // - This is done by having an imaginary no_snap_rect around the scrollbar
- // track. This extends about 8 times the width of the track on either side. When
- // a manipulation is in progress, the mouse is expected to stay within the
- // bounds of this rect. Assuming a standard scrollbar, 17px wide, this is how
- // it'd look like.
- // https://github.com/rahul8805/CompositorThreadedScrollbarDocs/blob/master/snap.PNG?raw=true
- // - When a pointerdown is received, record the original offset of the thumb.
- // - On every pointermove, check if the pointer is within the bounds of the
- // no_snap_rect. If false, snap to the initial_scroll_offset and stop processing
- // pointermove(s) until the pointer reenters the bounds of the rect.
- // - The moment the mouse re-enters the bounds of the no_snap_rect, we snap to
- // the initial_scroll_offset + event.PositionInWidget.
- // Thumb anchoring.
- // - During a thumb drag, if the pointer runs off the track, there should be no
- // additional scrolling until the pointer reenters the track and crosses the
- // original mousedown point.
- // - This is done by sending "clamped" deltas. The amount of scrollable delta is
- // computed using LayerTreeHostImpl::ComputeScrollDelta.
- // - Since the deltas are clamped, overscroll doesn't occur if it can't be
- // consumed by the CurrentlyScrollingNode.
- // Autoscroll play/pause.
- // - When the pointer moves in and out of bounds of a scrollbar part that can
- // initiate autoscrolls (like arrows or track), the autoscroll animation is
- // expected to play or pause accordingly.
- // - On every ScrollbarController::WillBeginMainFrame, the pointer location is
- // constantly checked and if it is outside the bounds of the scrollbar part that
- // initiated the autoscroll, the autoscroll is stopped.
- // - Similarly, when the pointer reenters the bounds, autoscroll is restarted
- // again. All the vital information during autoscrolling such the velocity,
- // direction, scroll layer length etc is held in
- // cc::ScrollbarController::AutoscrollState.
- // Shift + click.
- // - Doing a shift click on any part of a scrollbar track is supposed to do an
- // instant scroll to that location (such that the thumb is still centered on the
- // pointer).
- // - When the MouseEvent reaches the
- // InputHandlerProxy::RouteToTypeSpecificHandler, if the event is found to have
- // a "Shift" modifier, the ScrollbarController calculates the offset based on
- // the pointers current location on the track.
- // - Once the offset is determined, the InputHandlerProxy creates a GSU with
- // state that tells the LayerTreeHostImpl to perform a non-animated scroll to
- // the offset.
- // Continuous autoscrolling.
- // - This builds on top of the autoscolling implementation. "Continuous"
- // autoscrolling is when an autoscroll is in progress and the size of the
- // content keeps increasing. For eg: When you keep the down arrow pressed on
- // websites like Facebook, the autoscrolling is expected to keep on going until
- // the mouse is released.
- // - This is implemented by monitoring the length of the scroller layer at every
- // frame and if the length increases (and if autoscroll in the forward direction
- // is already in progress), the old animation is aborted and a new autoscroll
- // animation with the new scroller length is kicked off.
- namespace cc {
- class LayerTreeHostImpl;
- // This class is responsible for hit testing composited scrollbars, event
- // handling and creating gesture scroll deltas.
- class CC_EXPORT ScrollbarController {
- public:
- explicit ScrollbarController(LayerTreeHostImpl*);
- virtual ~ScrollbarController();
- // On Mac, the "jump to the spot that's clicked" setting can be dynamically
- // set via System Preferences. When enabled, the expectation is that regular
- // clicks on the scrollbar should make the scroller "jump" to the clicked
- // location rather than animated scrolling. Additionally, when this is enabled
- // and the user does an Option + click on the scrollbar, the scroller should
- // *not* jump to that spot (i.e it should be treated as a regular track
- // click). When this setting is disabled on the Mac, Option + click should
- // make the scroller jump and a regular click should animate the scroll
- // offset. On all other platforms, the "jump on click" option is available
- // (via Shift + click) but is not configurable.
- InputHandlerPointerResult HandlePointerDown(
- const gfx::PointF position_in_widget,
- const bool jump_key_modifier);
- InputHandlerPointerResult HandlePointerMove(
- const gfx::PointF position_in_widget);
- InputHandlerPointerResult HandlePointerUp(
- const gfx::PointF position_in_widget);
- bool AutoscrollTaskIsScheduled() const {
- return cancelable_autoscroll_task_ != nullptr;
- }
- bool ScrollbarScrollIsActive() const { return scrollbar_scroll_is_active_; }
- void DidRegisterScrollbar(ElementId element_id,
- ScrollbarOrientation orientation);
- void DidUnregisterScrollbar(ElementId element_id,
- ScrollbarOrientation orientation);
- ScrollbarLayerImplBase* ScrollbarLayer() const;
- void WillBeginImplFrame();
- void ResetState();
- PointerResultType HitTest(const gfx::PointF position_in_widget) const;
- private:
- FRIEND_TEST_ALL_PREFIXES(ScrollUnifiedLayerTreeHostImplTest,
- ThumbDragAfterJumpClick);
- FRIEND_TEST_ALL_PREFIXES(ScrollUnifiedLayerTreeHostImplTest,
- AbortAnimatedScrollBeforeStartingAutoscroll);
- FRIEND_TEST_ALL_PREFIXES(ScrollUnifiedLayerTreeHostImplTest,
- AutoscrollOnDeletedScrollbar);
- FRIEND_TEST_ALL_PREFIXES(ScrollUnifiedLayerTreeHostImplTest,
- ScrollOnLargeThumb);
- // "Autoscroll" here means the continuous scrolling that occurs when the
- // pointer is held down on a hit-testable area of the scrollbar such as an
- // arrows of the track itself.
- enum class AutoScrollDirection { AUTOSCROLL_FORWARD, AUTOSCROLL_BACKWARD };
- enum class AutoScrollStatus {
- // For when the 250ms delay before an autoscroll starts animating has not
- // yet elapsed
- AUTOSCROLL_WAITING,
- // For when the delay has elapsed, but the autoscroll cannot animate for
- // some reason (the scrollbar being unregistered)
- AUTOSCROLL_READY,
- // For when the autoscroll is animating
- AUTOSCROLL_SCROLLING
- };
- struct CC_EXPORT AutoScrollState {
- // Can only be either AUTOSCROLL_FORWARD or AUTOSCROLL_BACKWARD.
- AutoScrollDirection direction = AutoScrollDirection::AUTOSCROLL_FORWARD;
- AutoScrollStatus status = AutoScrollStatus::AUTOSCROLL_WAITING;
- // Stores the autoscroll velocity. The sign is used to set the "direction".
- float velocity = 0.f;
- // Used to track the scroller length while autoscrolling. Helpful for
- // setting up infinite scrolling.
- float scroll_layer_length = 0.f;
- // Used to lookup the rect corresponding to the ScrollbarPart so that
- // autoscroll animations can be played/paused depending on the current
- // pointer location.
- ScrollbarPart pressed_scrollbar_part;
- };
- struct CC_EXPORT DragState {
- // This marks the point at which the drag initiated (relative to the
- // scrollbar layer).
- gfx::PointF drag_origin;
- // This is needed for thumb snapping when the pointer moves too far away
- // from the track while scrolling.
- float scroll_position_at_start_;
- // The |scroller_displacement| indicates the scroll offset compensation that
- // needs to be applied when the scroller's length changes dynamically mid
- // thumb drag. This is needed done to ensure that the scroller does not jump
- // while a thumb drag is in progress.
- float scroller_displacement;
- float scroller_length_at_previous_move;
- };
- struct CC_EXPORT CapturedScrollbarMetadata {
- // Needed to retrieve the ScrollbarSet for a particular ElementId.
- ElementId scroll_element_id;
- // Needed to identify the correct scrollbar from the ScrollbarSet.
- ScrollbarOrientation orientation;
- };
- // Posts an autoscroll task based on the autoscroll state, with the given
- // delay
- void PostAutoscrollTask(const base::TimeDelta delay);
- // Initiates an autoscroll, setting the necessary status and starting the
- // animation, if possible
- void StartAutoScroll();
- // Starts/restarts an autoscroll animation based off of the information in
- // autoscroll_state_
- void StartAutoScrollAnimation();
- // Returns the DSF based on whether use-zoom-for-dsf is enabled.
- float ScreenSpaceScaleFactor() const;
- // Helper to convert scroll offset to autoscroll velocity.
- float InitialDeltaToAutoscrollVelocity(gfx::Vector2dF scroll_delta) const;
- // Returns the hit tested ScrollbarPart based on the position_in_widget.
- ScrollbarPart GetScrollbarPartFromPointerDown(
- const gfx::PointF position_in_widget) const;
- // Clamps |scroll_delta| based on the available scrollable amount of
- // |target_node|. The returned delta includes the page scale factor and is
- // appropriate for use directly as a delta for GSU.
- gfx::Vector2dF ComputeClampedDelta(const ScrollNode& target_node,
- const gfx::Vector2dF& scroll_delta) const;
- // Returns the rect for the ScrollbarPart.
- gfx::Rect GetRectForScrollbarPart(const ScrollbarPart scrollbar_part) const;
- LayerImpl* GetLayerHitByPoint(const gfx::PointF position_in_widget) const;
- // Returns scroll delta as Vector2dF based on which ScrollbarPart was hit
- // tested.
- gfx::Vector2dF GetScrollDeltaForScrollbarPart(
- const ScrollbarPart scrollbar_part,
- const bool jump_key_modifier) const;
- // Returns scroll delta in the direction of the scrollbar's orientation.
- float GetScrollDistanceForScrollbarPart(const ScrollbarPart scrollbar_part,
- const bool jump_key_modifier) const;
- // Makes position_in_widget relative to the scrollbar.
- gfx::PointF GetScrollbarRelativePosition(const gfx::PointF position_in_widget,
- bool* clipped) const;
- // Computes an aritificial drag origin for jump clicks, to give the scrollbar
- // a proper place to snap back to on a jump click then drag
- gfx::PointF DragOriginForJumpClick(
- const ScrollbarLayerImplBase* scrollbar) const;
- // Decides if the scroller should snap to the offset that it was
- // originally at (i.e the offset before the thumb drag).
- bool SnapToDragOrigin(const gfx::PointF pointer_position_in_widget) const;
- // Decides whether a track autoscroll should be aborted (or restarted) due to
- // the thumb reaching the pointer or the pointer leaving (or re-entering) the
- // bounds.
- void RecomputeAutoscrollStateIfNeeded();
- // Shift (or "Option" in case of Mac) + click is expected to do a non-animated
- // jump to a certain offset.
- float GetScrollDistanceForAbsoluteJump() const;
- // Determines if the delta needs to be animated.
- ui::ScrollGranularity Granularity(const ScrollbarPart scrollbar_part,
- bool jump_key_modifier) const;
- // Calculates the distance based on position_in_widget and drag_origin.
- float GetScrollDistanceForDragPosition(
- const gfx::PointF pointer_position_in_widget) const;
- // Returns the ratio of the scroller length to the scrollbar length. This is
- // needed to scale the scroll delta for thumb drag.
- float GetScrollerToScrollbarRatio() const;
- float GetViewportLength() const;
- // Returns the pixel distance for a percent-based scroll of the scrollbar
- float GetScrollDistanceForPercentBasedScroll() const;
- // Returns the page scale factor (i.e. pinch zoom factor). This is relevant
- // for root viewport scrollbar scrolling.
- float GetPageScaleFactorForScroll() const;
- raw_ptr<LayerTreeHostImpl> layer_tree_host_impl_;
- // Used to safeguard against firing GSE without firing GSB and GSU. For
- // example, if mouse is pressed outside the scrollbar but released after
- // moving inside the scrollbar, a GSE will get queued up without this flag.
- bool scrollbar_scroll_is_active_;
- // This is relative to the RenderWidget's origin.
- gfx::PointF last_known_pointer_position_;
- // Set only while interacting with the scrollbar (eg: drag, click etc).
- absl::optional<CapturedScrollbarMetadata> captured_scrollbar_metadata_;
- // Holds information pertaining to autoscrolling. This member is empty if and
- // only if an autoscroll is *not* in progress or scheduled
- absl::optional<AutoScrollState> autoscroll_state_;
- // Holds information pertaining to thumb drags. Useful while making decisions
- // about thumb anchoring/snapping.
- absl::optional<DragState> drag_state_;
- // Used to track if a GSU was processed for the current frame or not. Without
- // this, thumb drag will appear jittery. The reason this happens is because
- // when the first GSU is processed, it gets queued in the compositor thread
- // event queue. So a second request within the same frame will end up
- // calculating an incorrect delta (as ComputeThumbQuadRect would not have
- // accounted for the delta in the first GSU that was not yet dispatched and
- // pointermoves are not VSync aligned).
- bool drag_processed_for_current_frame_;
- std::unique_ptr<base::CancelableOnceClosure> cancelable_autoscroll_task_;
- };
- } // namespace cc
- #endif // CC_INPUT_SCROLLBAR_CONTROLLER_H_
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