/*
* Copyright 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.compose.foundation
import androidx.compose.runtime.Composable
import androidx.compose.runtime.Stable
import androidx.compose.ui.Modifier
import androidx.compose.ui.geometry.Offset
import androidx.compose.ui.input.nestedscroll.NestedScrollSource
import androidx.compose.ui.unit.Velocity
/**
* Controller to control the overscroll logic for a particular scrollable container.
*
* This entity defines the "how" of the overscroll effect. If the default platform effect is needed,
* consider using [ScrollableDefaults.overscrollEffect]. In order for overscroll to work,
* the controller is supposed to be passed to [scrollable] modifier to receive the data of
* overscroll, and then applied where appropriate using [overscroll] modifier.
*
* @sample androidx.compose.foundation.samples.OverscrollSample
*/
@ExperimentalFoundationApi
@Stable
interface OverscrollEffect {
/**
* Consume any overscroll before the scroll happens if needed.
*
* This is usually relevant when the overscroll expresses the effect that is needed to be
* negated first before actually scrolling. The example might be a spring-based overscroll,
* where you want to release the tension of a spring before starting to scroll to provide a
* good user-experience.
*
* @param scrollDelta the original delta to scroll
* @param pointerPosition position of the pointer causing the scroll, if known
* @param source source of the scroll event
*
* @return the amount of scroll consumed that won't be available for scrollable container
* anymore
*/
fun consumePreScroll(
scrollDelta: Offset,
pointerPosition: Offset?,
source: NestedScrollSource
): Offset
/**
* Process scroll delta that is available after the scroll iteration is over.
*
* This is the main method to show an overscroll, as [overscrollDelta] will be a
* non-[zero][Offset.Zero] only if the scroll is happening at the bound of a scrollable
* container.
*
* @param initialDragDelta initial drag delta before any consumption was made
* @param overscrollDelta the amount of overscroll left after the scroll process
* @param pointerPosition the pointer location in the bounds of the container
* @param source source of the scroll event
*/
fun consumePostScroll(
initialDragDelta: Offset,
overscrollDelta: Offset,
pointerPosition: Offset?,
source: NestedScrollSource
)
/**
* Consume any velocity for the over scroll effect before the fling happens.
*
* relevant when the overscroll expresses the effect that is needed to be
* negated (or increased) first before actually scrolling. The example might be a spring-based
* overscroll, where you want to release the tension of a spring before starting to scroll to
* provide a good user-experience.
*
* @param velocity velocity available to a scrolling container before flinging
*
* @return the amount of velocity that overscroll effect consumed that won't be available for
* fling operation
*/
suspend fun consumePreFling(velocity: Velocity): Velocity
/**
* Feed and process velocity overscroll to show an effect.
*
* @param velocity the amount of velocity that is left for overscroll after the fling happened.
*/
suspend fun consumePostFling(velocity: Velocity)
/**
* Whether the overscroll effect is enabled or not. If it is not enabled, [scrollable] won't
* send the events to this effect.
*/
var isEnabled: Boolean
/**
* Whether over scroll within this controller is currently on progress or not, e.g. if the
* overscroll effect is playing animation or shown/interactable in any other way.
*
* @return true if there is over scroll happening at the time of the call, false otherwise
*/
val isInProgress: Boolean
/**
* A modifier that will apply the overscroll effect as desired
*/
val effectModifier: Modifier
}
@OptIn(ExperimentalFoundationApi::class)
@Composable
internal expect fun rememberOverscrollEffect(): OverscrollEffect
/**
* Modifier to apply the overscroll as specified by [OverscrollEffect]
*
* This modifier is a convenience method to call [OverscrollEffect.effectModifier], which
* performs the actual overscroll logic. Note that this modifier is the representation of the
* overscroll on the UI, to make overscroll events to be propagated to the [OverscrollEffect],
* you have to pass it to [scrollable].
*
* @sample androidx.compose.foundation.samples.OverscrollSample
*
* @param overscrollEffect controller that defines the behavior and the overscroll state.
*/
@ExperimentalFoundationApi
fun Modifier.overscroll(overscrollEffect: OverscrollEffect): Modifier =
this.then(overscrollEffect.effectModifier)