WindowInfo.kt

/*
 * 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.ui.platform

import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.Stable
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.rememberUpdatedState
import androidx.compose.runtime.snapshotFlow
import androidx.compose.ui.ExperimentalComposeUiApi
import androidx.compose.ui.input.pointer.EmptyPointerKeyboardModifiers
import androidx.compose.ui.input.pointer.PointerKeyboardModifiers
import kotlinx.coroutines.flow.collect

/**
 * Provides information about the Window that is hosting this compose hierarchy.
 */
@Stable
interface WindowInfo {
    /**
     * Indicates whether the window hosting this compose hierarchy is in focus.
     *
     * When there are multiple windows visible, either in a multi-window environment or if a
     * popup or dialog is visible, this property can be used to determine if the current window
     * is in focus.
     */
    val isWindowFocused: Boolean

    /**
     * Indicates the state of keyboard modifiers (pressed or not).
     */
    @Suppress("OPT_IN_MARKER_ON_WRONG_TARGET")
    @get:ExperimentalComposeUiApi
    val keyboardModifiers: PointerKeyboardModifiers
        get() = WindowInfoImpl.GlobalKeyboardModifiers.value
}

@Composable
internal fun WindowFocusObserver(onWindowFocusChanged: (isWindowFocused: Boolean) -> Unit) {
    val windowInfo = LocalWindowInfo.current
    val callback = rememberUpdatedState(onWindowFocusChanged)
    LaunchedEffect(windowInfo) {
        snapshotFlow { windowInfo.isWindowFocused }.collect { callback.value(it) }
    }
}

internal class WindowInfoImpl : WindowInfo {
    private val _isWindowFocused = mutableStateOf(false)

    override var isWindowFocused: Boolean
        set(value) { _isWindowFocused.value = value }
        get() = _isWindowFocused.value

    @Suppress("OPT_IN_MARKER_ON_WRONG_TARGET")
    @get:ExperimentalComposeUiApi
    override var keyboardModifiers: PointerKeyboardModifiers
        get() = GlobalKeyboardModifiers.value
        set(value) { GlobalKeyboardModifiers.value = value }

    companion object {
        // One instance across all windows makes sense, since the state of KeyboardModifiers is
        // common for all windows.
        internal val GlobalKeyboardModifiers = mutableStateOf(EmptyPointerKeyboardModifiers())
    }
}