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Bug 1219296 - Factor out the algorithm that computes a scroll snap destination into a reusable form. r=kats

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MozReview-Commit-ID: KyU67pXEJus

--HG--
extra : rebase_source : c1dfbe948dd8d98e549612287ca48e507adf5aee
This commit is contained in:
Botond Ballo 2016-03-21 21:32:28 -04:00
parent e33fc6e896
commit c2325214db
4 changed files with 358 additions and 292 deletions
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311
layout/generic/ScrollSnap.cpp Normal file
View File

@ -0,0 +1,311 @@
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "FrameMetrics.h"
#include "ScrollSnap.h"
#include "mozilla/Maybe.h"
#include "mozilla/Preferences.h"
#include "nsLineLayout.h"
namespace mozilla {
using layers::ScrollSnapInfo;
/**
* Stores candidate snapping edges.
*/
class SnappingEdgeCallback {
public:
virtual void AddHorizontalEdge(nscoord aEdge) = 0;
virtual void AddVerticalEdge(nscoord aEdge) = 0;
virtual void AddHorizontalEdgeInterval(const nsRect &aScrollRange,
nscoord aInterval,
nscoord aOffset) = 0;
virtual void AddVerticalEdgeInterval(const nsRect &aScrollRange,
nscoord aInterval,
nscoord aOffset) = 0;
};
/**
* Keeps track of the current best edge to snap to. The criteria for
* adding an edge depends on the scrolling unit.
*/
class CalcSnapPoints : public SnappingEdgeCallback {
public:
CalcSnapPoints(nsIScrollableFrame::ScrollUnit aUnit,
const nsPoint& aDestination,
const nsPoint& aStartPos);
virtual void AddHorizontalEdge(nscoord aEdge) override;
virtual void AddVerticalEdge(nscoord aEdge) override;
virtual void AddHorizontalEdgeInterval(const nsRect &aScrollRange,
nscoord aInterval, nscoord aOffset)
override;
virtual void AddVerticalEdgeInterval(const nsRect &aScrollRange,
nscoord aInterval, nscoord aOffset)
override;
void AddEdge(nscoord aEdge,
nscoord aDestination,
nscoord aStartPos,
nscoord aScrollingDirection,
nscoord* aBestEdge,
bool* aEdgeFound);
void AddEdgeInterval(nscoord aInterval,
nscoord aMinPos,
nscoord aMaxPos,
nscoord aOffset,
nscoord aDestination,
nscoord aStartPos,
nscoord aScrollingDirection,
nscoord* aBestEdge,
bool* aEdgeFound);
nsPoint GetBestEdge() const;
protected:
nsIScrollableFrame::ScrollUnit mUnit;
nsPoint mDestination; // gives the position after scrolling but before snapping
nsPoint mStartPos; // gives the position before scrolling
nsIntPoint mScrollingDirection; // always -1, 0, or 1
nsPoint mBestEdge; // keeps track of the position of the current best edge
bool mHorizontalEdgeFound; // true if mBestEdge.x is storing a valid horizontal edge
bool mVerticalEdgeFound; // true if mBestEdge.y is storing a valid vertical edge
};
CalcSnapPoints::CalcSnapPoints(nsIScrollableFrame::ScrollUnit aUnit,
const nsPoint& aDestination,
const nsPoint& aStartPos)
{
mUnit = aUnit;
mDestination = aDestination;
mStartPos = aStartPos;
nsPoint direction = aDestination - aStartPos;
mScrollingDirection = nsIntPoint(0,0);
if (direction.x < 0) {
mScrollingDirection.x = -1;
}
if (direction.x > 0) {
mScrollingDirection.x = 1;
}
if (direction.y < 0) {
mScrollingDirection.y = -1;
}
if (direction.y > 0) {
mScrollingDirection.y = 1;
}
mBestEdge = aDestination;
mHorizontalEdgeFound = false;
mVerticalEdgeFound = false;
}
nsPoint
CalcSnapPoints::GetBestEdge() const
{
return nsPoint(mVerticalEdgeFound ? mBestEdge.x : mStartPos.x,
mHorizontalEdgeFound ? mBestEdge.y : mStartPos.y);
}
void
CalcSnapPoints::AddHorizontalEdge(nscoord aEdge)
{
AddEdge(aEdge, mDestination.y, mStartPos.y, mScrollingDirection.y, &mBestEdge.y,
&mHorizontalEdgeFound);
}
void
CalcSnapPoints::AddVerticalEdge(nscoord aEdge)
{
AddEdge(aEdge, mDestination.x, mStartPos.x, mScrollingDirection.x, &mBestEdge.x,
&mVerticalEdgeFound);
}
void
CalcSnapPoints::AddHorizontalEdgeInterval(const nsRect &aScrollRange,
nscoord aInterval, nscoord aOffset)
{
AddEdgeInterval(aInterval, aScrollRange.y, aScrollRange.YMost(), aOffset,
mDestination.y, mStartPos.y, mScrollingDirection.y,
&mBestEdge.y, &mHorizontalEdgeFound);
}
void
CalcSnapPoints::AddVerticalEdgeInterval(const nsRect &aScrollRange,
nscoord aInterval, nscoord aOffset)
{
AddEdgeInterval(aInterval, aScrollRange.x, aScrollRange.XMost(), aOffset,
mDestination.x, mStartPos.x, mScrollingDirection.x,
&mBestEdge.x, &mVerticalEdgeFound);
}
void
CalcSnapPoints::AddEdge(nscoord aEdge, nscoord aDestination, nscoord aStartPos,
nscoord aScrollingDirection, nscoord* aBestEdge,
bool *aEdgeFound)
{
// nsIScrollableFrame::DEVICE_PIXELS indicates that we are releasing a drag
// gesture or any other user input event that sets an absolute scroll
// position. In this case, scroll snapping is expected to travel in any
// direction. Otherwise, we will restrict the direction of the scroll
// snapping movement based on aScrollingDirection.
if (mUnit != nsIScrollableFrame::DEVICE_PIXELS) {
// Unless DEVICE_PIXELS, we only want to snap to points ahead of the
// direction we are scrolling
if (aScrollingDirection == 0) {
// The scroll direction is neutral - will not hit a snap point.
return;
}
// nsIScrollableFrame::WHOLE indicates that we are navigating to "home" or
// "end". In this case, we will always select the first or last snap point
// regardless of the direction of the scroll. Otherwise, we will select
// scroll snapping points only in the direction specified by
// aScrollingDirection.
if (mUnit != nsIScrollableFrame::WHOLE) {
// Direction of the edge from the current position (before scrolling) in
// the direction of scrolling
nscoord direction = (aEdge - aStartPos) * aScrollingDirection;
if (direction <= 0) {
// The edge is not in the direction we are scrolling, skip it.
return;
}
}
}
if (!*aEdgeFound) {
*aBestEdge = aEdge;
*aEdgeFound = true;
return;
}
if (mUnit == nsIScrollableFrame::DEVICE_PIXELS ||
mUnit == nsIScrollableFrame::LINES) {
if (std::abs(aEdge - aDestination) < std::abs(*aBestEdge - aDestination)) {
*aBestEdge = aEdge;
}
} else if (mUnit == nsIScrollableFrame::PAGES) {
// distance to the edge from the scrolling destination in the direction of scrolling
nscoord overshoot = (aEdge - aDestination) * aScrollingDirection;
// distance to the current best edge from the scrolling destination in the direction of scrolling
nscoord curOvershoot = (*aBestEdge - aDestination) * aScrollingDirection;
// edges between the current position and the scrolling destination are favoured
// to preserve context
if (overshoot < 0 && (overshoot > curOvershoot || curOvershoot >= 0)) {
*aBestEdge = aEdge;
}
// if there are no edges between the current position and the scrolling destination
// the closest edge beyond the destination is used
if (overshoot > 0 && overshoot < curOvershoot) {
*aBestEdge = aEdge;
}
} else if (mUnit == nsIScrollableFrame::WHOLE) {
// the edge closest to the top/bottom/left/right is used, depending on scrolling direction
if (aScrollingDirection > 0 && aEdge > *aBestEdge) {
*aBestEdge = aEdge;
} else if (aScrollingDirection < 0 && aEdge < *aBestEdge) {
*aBestEdge = aEdge;
}
} else {
NS_ERROR("Invalid scroll mode");
return;
}
}
void
CalcSnapPoints::AddEdgeInterval(nscoord aInterval, nscoord aMinPos,
nscoord aMaxPos, nscoord aOffset,
nscoord aDestination, nscoord aStartPos,
nscoord aScrollingDirection,
nscoord* aBestEdge, bool *aEdgeFound)
{
if (aInterval == 0) {
// When interval is 0, there are no scroll snap points.
// Avoid division by zero and bail.
return;
}
// The only possible candidate interval snap points are the edges immediately
// surrounding aDestination.
// aDestination must be clamped to the scroll
// range in order to handle cases where the best matching snap point would
// result in scrolling out of bounds. This clamping must be prior to
// selecting the two interval edges.
nscoord clamped = std::max(std::min(aDestination, aMaxPos), aMinPos);
// Add each edge in the interval immediately before aTarget and after aTarget
// Do not add edges that are out of range.
nscoord r = (clamped + aOffset) % aInterval;
if (r < aMinPos) {
r += aInterval;
}
nscoord edge = clamped - r;
if (edge >= aMinPos && edge <= aMaxPos) {
AddEdge(edge, aDestination, aStartPos, aScrollingDirection, aBestEdge,
aEdgeFound);
}
edge += aInterval;
if (edge >= aMinPos && edge <= aMaxPos) {
AddEdge(edge, aDestination, aStartPos, aScrollingDirection, aBestEdge,
aEdgeFound);
}
}
static void
ProcessScrollSnapCoordinates(SnappingEdgeCallback& aCallback,
const nsTArray<nsPoint>& aScrollSnapCoordinates,
const nsPoint& aScrollSnapDestination) {
for (nsPoint snapCoords : aScrollSnapCoordinates) {
// Make them relative to the scroll snap destination.
snapCoords -= aScrollSnapDestination;
aCallback.AddVerticalEdge(snapCoords.x);
aCallback.AddHorizontalEdge(snapCoords.y);
}
}
Maybe<nsPoint> ScrollSnapUtils::GetSnapPointForDestination(
const ScrollSnapInfo& aSnapInfo,
nsIScrollableFrame::ScrollUnit aUnit,
const nsSize& aScrollPortSize,
const nsRect& aScrollRange,
const nsPoint& aStartPos,
const nsPoint& aDestination)
{
if (aSnapInfo.mScrollSnapTypeY == NS_STYLE_SCROLL_SNAP_TYPE_NONE &&
aSnapInfo.mScrollSnapTypeX == NS_STYLE_SCROLL_SNAP_TYPE_NONE) {
return Nothing();
}
nsPoint destPos = aSnapInfo.mScrollSnapDestination;
CalcSnapPoints calcSnapPoints(aUnit, aDestination, aStartPos);
if (aSnapInfo.mScrollSnapIntervalX.isSome()) {
nscoord interval = aSnapInfo.mScrollSnapIntervalX.value();
calcSnapPoints.AddVerticalEdgeInterval(aScrollRange, interval, destPos.x);
}
if (aSnapInfo.mScrollSnapIntervalY.isSome()) {
nscoord interval = aSnapInfo.mScrollSnapIntervalY.value();
calcSnapPoints.AddHorizontalEdgeInterval(aScrollRange, interval, destPos.y);
}
ProcessScrollSnapCoordinates(calcSnapPoints, aSnapInfo.mScrollSnapCoordinates, destPos);
bool snapped = false;
nsPoint finalPos = calcSnapPoints.GetBestEdge();
nscoord proximityThreshold =
Preferences::GetInt("layout.css.scroll-snap.proximity-threshold", 0);
proximityThreshold = nsPresContext::CSSPixelsToAppUnits(proximityThreshold);
if (aSnapInfo.mScrollSnapTypeY == NS_STYLE_SCROLL_SNAP_TYPE_PROXIMITY &&
std::abs(aDestination.y - finalPos.y) > proximityThreshold) {
finalPos.y = aDestination.y;
} else {
snapped = true;
}
if (aSnapInfo.mScrollSnapTypeX == NS_STYLE_SCROLL_SNAP_TYPE_PROXIMITY &&
std::abs(aDestination.x - finalPos.x) > proximityThreshold) {
finalPos.x = aDestination.x;
} else {
snapped = true;
}
return snapped ? Some(finalPos) : Nothing();
}
} // namespace mozilla

37
layout/generic/ScrollSnap.h Normal file
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@ -0,0 +1,37 @@
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef mozilla_layout_ScrollSnap_h_
#define mozilla_layout_ScrollSnap_h_
namespace mozilla {
namespace layers {
struct ScrollSnapInfo;
}
struct ScrollSnapUtils {
/**
* GetSnapPointForDestination determines which point to snap to after
* scrolling. |aStartPos| gives the position before scrolling and
* |aDestination| gives the position after scrolling, with no snapping.
* Behaviour is dependent on the value of |aUnit|.
* |aSnapInfo|, |aScrollPortSize|, and |aScrollRange| are characteristics
* of the scroll frame for which snapping is being performed.
* If a suitable snap point could be found, it is returned. Otherwise, an
* empty Maybe is returned.
*/
static Maybe<nsPoint> GetSnapPointForDestination(
const layers::ScrollSnapInfo& aSnapInfo,
nsIScrollableFrame::ScrollUnit aUnit,
const nsSize& aScrollPortSize,
const nsRect& aScrollRange,
const nsPoint& aStartPos,
const nsPoint& aDestination);
};
} // namespace mozilla
#endif // mozilla_layout_ScrollSnap_h_

2
layout/generic/moz.build
View File

@ -96,6 +96,7 @@ EXPORTS += [
'nsTextRunTransformations.h',
'RubyUtils.h',
'ScrollbarActivity.h',
'ScrollSnap.h',
'Visibility.h',
]
@ -166,6 +167,7 @@ UNIFIED_SOURCES += [
'nsViewportFrame.cpp',
'RubyUtils.cpp',
'ScrollbarActivity.cpp',
'ScrollSnap.cpp',
'ScrollVelocityQueue.cpp',
'StickyScrollContainer.cpp',
'SummaryFrame.cpp',

300
layout/generic/nsGfxScrollFrame.cpp
View File

@ -59,6 +59,7 @@
#include "gfxPlatform.h"
#include "gfxPrefs.h"
#include "AsyncScrollBase.h"
#include "ScrollSnap.h"
#include "UnitTransforms.h"
#include "nsPluginFrame.h"
#include <mozilla/layers/AxisPhysicsModel.h>
@ -5774,254 +5775,6 @@ nsIScrollableFrame::GetPerceivedScrollingDirections() const
return directions;
}
/**
* Stores candidate snapping edges.
*/
class SnappingEdgeCallback {
public:
virtual void AddHorizontalEdge(nscoord aEdge) = 0;
virtual void AddVerticalEdge(nscoord aEdge) = 0;
virtual void AddHorizontalEdgeInterval(const nsRect &aScrollRange,
nscoord aInterval,
nscoord aOffset) = 0;
virtual void AddVerticalEdgeInterval(const nsRect &aScrollRange,
nscoord aInterval,
nscoord aOffset) = 0;
};
/**
* Keeps track of the current best edge to snap to. The criteria for
* adding an edge depends on the scrolling unit.
*/
class CalcSnapPoints : public SnappingEdgeCallback {
public:
CalcSnapPoints(nsIScrollableFrame::ScrollUnit aUnit,
const nsPoint& aDestination,
const nsPoint& aStartPos);
virtual void AddHorizontalEdge(nscoord aEdge) override;
virtual void AddVerticalEdge(nscoord aEdge) override;
virtual void AddHorizontalEdgeInterval(const nsRect &aScrollRange,
nscoord aInterval, nscoord aOffset)
override;
virtual void AddVerticalEdgeInterval(const nsRect &aScrollRange,
nscoord aInterval, nscoord aOffset)
override;
void AddEdge(nscoord aEdge,
nscoord aDestination,
nscoord aStartPos,
nscoord aScrollingDirection,
nscoord* aBestEdge,
bool* aEdgeFound);
void AddEdgeInterval(nscoord aInterval,
nscoord aMinPos,
nscoord aMaxPos,
nscoord aOffset,
nscoord aDestination,
nscoord aStartPos,
nscoord aScrollingDirection,
nscoord* aBestEdge,
bool* aEdgeFound);
nsPoint GetBestEdge() const;
protected:
nsIScrollableFrame::ScrollUnit mUnit;
nsPoint mDestination; // gives the position after scrolling but before snapping
nsPoint mStartPos; // gives the position before scrolling
nsIntPoint mScrollingDirection; // always -1, 0, or 1
nsPoint mBestEdge; // keeps track of the position of the current best edge
bool mHorizontalEdgeFound; // true if mBestEdge.x is storing a valid horizontal edge
bool mVerticalEdgeFound; // true if mBestEdge.y is storing a valid vertical edge
};
CalcSnapPoints::CalcSnapPoints(nsIScrollableFrame::ScrollUnit aUnit,
const nsPoint& aDestination,
const nsPoint& aStartPos)
{
mUnit = aUnit;
mDestination = aDestination;
mStartPos = aStartPos;
nsPoint direction = aDestination - aStartPos;
mScrollingDirection = nsIntPoint(0,0);
if (direction.x < 0) {
mScrollingDirection.x = -1;
}
if (direction.x > 0) {
mScrollingDirection.x = 1;
}
if (direction.y < 0) {
mScrollingDirection.y = -1;
}
if (direction.y > 0) {
mScrollingDirection.y = 1;
}
mBestEdge = aDestination;
mHorizontalEdgeFound = false;
mVerticalEdgeFound = false;
}
nsPoint
CalcSnapPoints::GetBestEdge() const
{
return nsPoint(mVerticalEdgeFound ? mBestEdge.x : mStartPos.x,
mHorizontalEdgeFound ? mBestEdge.y : mStartPos.y);
}
void
CalcSnapPoints::AddHorizontalEdge(nscoord aEdge)
{
AddEdge(aEdge, mDestination.y, mStartPos.y, mScrollingDirection.y, &mBestEdge.y,
&mHorizontalEdgeFound);
}
void
CalcSnapPoints::AddVerticalEdge(nscoord aEdge)
{
AddEdge(aEdge, mDestination.x, mStartPos.x, mScrollingDirection.x, &mBestEdge.x,
&mVerticalEdgeFound);
}
void
CalcSnapPoints::AddHorizontalEdgeInterval(const nsRect &aScrollRange,
nscoord aInterval, nscoord aOffset)
{
AddEdgeInterval(aInterval, aScrollRange.y, aScrollRange.YMost(), aOffset,
mDestination.y, mStartPos.y, mScrollingDirection.y,
&mBestEdge.y, &mHorizontalEdgeFound);
}
void
CalcSnapPoints::AddVerticalEdgeInterval(const nsRect &aScrollRange,
nscoord aInterval, nscoord aOffset)
{
AddEdgeInterval(aInterval, aScrollRange.x, aScrollRange.XMost(), aOffset,
mDestination.x, mStartPos.x, mScrollingDirection.x,
&mBestEdge.x, &mVerticalEdgeFound);
}
void
CalcSnapPoints::AddEdge(nscoord aEdge, nscoord aDestination, nscoord aStartPos,
nscoord aScrollingDirection, nscoord* aBestEdge,
bool *aEdgeFound)
{
// nsIScrollableFrame::DEVICE_PIXELS indicates that we are releasing a drag
// gesture or any other user input event that sets an absolute scroll
// position. In this case, scroll snapping is expected to travel in any
// direction. Otherwise, we will restrict the direction of the scroll
// snapping movement based on aScrollingDirection.
if (mUnit != nsIScrollableFrame::DEVICE_PIXELS) {
// Unless DEVICE_PIXELS, we only want to snap to points ahead of the
// direction we are scrolling
if (aScrollingDirection == 0) {
// The scroll direction is neutral - will not hit a snap point.
return;
}
// nsIScrollableFrame::WHOLE indicates that we are navigating to "home" or
// "end". In this case, we will always select the first or last snap point
// regardless of the direction of the scroll. Otherwise, we will select
// scroll snapping points only in the direction specified by
// aScrollingDirection.
if (mUnit != nsIScrollableFrame::WHOLE) {
// Direction of the edge from the current position (before scrolling) in
// the direction of scrolling
nscoord direction = (aEdge - aStartPos) * aScrollingDirection;
if (direction <= 0) {
// The edge is not in the direction we are scrolling, skip it.
return;
}
}
}
if (!*aEdgeFound) {
*aBestEdge = aEdge;
*aEdgeFound = true;
return;
}
if (mUnit == nsIScrollableFrame::DEVICE_PIXELS ||
mUnit == nsIScrollableFrame::LINES) {
if (std::abs(aEdge - aDestination) < std::abs(*aBestEdge - aDestination)) {
*aBestEdge = aEdge;
}
} else if (mUnit == nsIScrollableFrame::PAGES) {
// distance to the edge from the scrolling destination in the direction of scrolling
nscoord overshoot = (aEdge - aDestination) * aScrollingDirection;
// distance to the current best edge from the scrolling destination in the direction of scrolling
nscoord curOvershoot = (*aBestEdge - aDestination) * aScrollingDirection;
// edges between the current position and the scrolling destination are favoured
// to preserve context
if (overshoot < 0 && (overshoot > curOvershoot || curOvershoot >= 0)) {
*aBestEdge = aEdge;
}
// if there are no edges between the current position and the scrolling destination
// the closest edge beyond the destination is used
if (overshoot > 0 && overshoot < curOvershoot) {
*aBestEdge = aEdge;
}
} else if (mUnit == nsIScrollableFrame::WHOLE) {
// the edge closest to the top/bottom/left/right is used, depending on scrolling direction
if (aScrollingDirection > 0 && aEdge > *aBestEdge) {
*aBestEdge = aEdge;
} else if (aScrollingDirection < 0 && aEdge < *aBestEdge) {
*aBestEdge = aEdge;
}
} else {
NS_ERROR("Invalid scroll mode");
return;
}
}
void
CalcSnapPoints::AddEdgeInterval(nscoord aInterval, nscoord aMinPos,
nscoord aMaxPos, nscoord aOffset,
nscoord aDestination, nscoord aStartPos,
nscoord aScrollingDirection,
nscoord* aBestEdge, bool *aEdgeFound)
{
if (aInterval == 0) {
// When interval is 0, there are no scroll snap points.
// Avoid division by zero and bail.
return;
}
// The only possible candidate interval snap points are the edges immediately
// surrounding aDestination.
// aDestination must be clamped to the scroll
// range in order to handle cases where the best matching snap point would
// result in scrolling out of bounds. This clamping must be prior to
// selecting the two interval edges.
nscoord clamped = std::max(std::min(aDestination, aMaxPos), aMinPos);
// Add each edge in the interval immediately before aTarget and after aTarget
// Do not add edges that are out of range.
nscoord r = (clamped + aOffset) % aInterval;
if (r < aMinPos) {
r += aInterval;
}
nscoord edge = clamped - r;
if (edge >= aMinPos && edge <= aMaxPos) {
AddEdge(edge, aDestination, aStartPos, aScrollingDirection, aBestEdge,
aEdgeFound);
}
edge += aInterval;
if (edge >= aMinPos && edge <= aMaxPos) {
AddEdge(edge, aDestination, aStartPos, aScrollingDirection, aBestEdge,
aEdgeFound);
}
}
static void
ProcessScrollSnapCoordinates(SnappingEdgeCallback& aCallback,
const nsTArray<nsPoint>& aScrollSnapCoordinates,
const nsPoint& aScrollSnapDestination) {
for (nsPoint snapCoords : aScrollSnapCoordinates) {
// Make them relative to the scroll snap destination.
snapCoords -= aScrollSnapDestination;
aCallback.AddVerticalEdge(snapCoords.x);
aCallback.AddHorizontalEdge(snapCoords.y);
}
}
/**
* Collect the scroll-snap-coordinates of frames in the subtree rooted at
* |aFrame|, relative to |aScrolledFrame|, into |aOutCoords|.
@ -6126,51 +5879,14 @@ ScrollFrameHelper::GetSnapPointForDestination(nsIScrollableFrame::ScrollUnit aUn
nsPoint aStartPos,
nsPoint &aDestination)
{
ScrollSnapInfo snapInfo = GetScrollSnapInfo();
if (snapInfo.mScrollSnapTypeY == NS_STYLE_SCROLL_SNAP_TYPE_NONE &&
snapInfo.mScrollSnapTypeX == NS_STYLE_SCROLL_SNAP_TYPE_NONE) {
Maybe<nsPoint> snapPoint = ScrollSnapUtils::GetSnapPointForDestination(
GetScrollSnapInfo(), aUnit, mScrollPort.Size(),
GetScrollRangeForClamping(), aStartPos, aDestination);
if (snapPoint) {
aDestination = snapPoint.ref();
return true;
}
return false;
}
nsSize scrollPortSize = mScrollPort.Size();
nsRect scrollRange = GetScrollRangeForClamping();
nsPoint destPos = snapInfo.mScrollSnapDestination;
CalcSnapPoints calcSnapPoints(aUnit, aDestination, aStartPos);
if (snapInfo.mScrollSnapIntervalX.isSome()) {
nscoord interval = snapInfo.mScrollSnapIntervalX.value();
calcSnapPoints.AddVerticalEdgeInterval(scrollRange, interval, destPos.x);
}
if (snapInfo.mScrollSnapIntervalY.isSome()) {
nscoord interval = snapInfo.mScrollSnapIntervalY.value();
calcSnapPoints.AddHorizontalEdgeInterval(scrollRange, interval, destPos.y);
}
ProcessScrollSnapCoordinates(calcSnapPoints, snapInfo.mScrollSnapCoordinates, destPos);
bool snapped = false;
nsPoint finalPos = calcSnapPoints.GetBestEdge();
nscoord proximityThreshold =
Preferences::GetInt("layout.css.scroll-snap.proximity-threshold", 0);
proximityThreshold = nsPresContext::CSSPixelsToAppUnits(proximityThreshold);
if (snapInfo.mScrollSnapTypeY == NS_STYLE_SCROLL_SNAP_TYPE_PROXIMITY &&
std::abs(aDestination.y - finalPos.y) > proximityThreshold) {
finalPos.y = aDestination.y;
} else {
snapped = true;
}
if (snapInfo.mScrollSnapTypeX == NS_STYLE_SCROLL_SNAP_TYPE_PROXIMITY &&
std::abs(aDestination.x - finalPos.x) > proximityThreshold) {
finalPos.x = aDestination.x;
} else {
snapped = true;
}
if (snapped) {
aDestination = finalPos;
}
return snapped;
}
bool