Support scrolling with mouse wheel in reader

app/src/main/kotlin/com/hippo/ehviewer/ui/reader/GalleryPager.kt

@@ -5,13 +5,20 @@ import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.lazy.LazyListState
 import androidx.compose.foundation.pager.PagerState
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberUpdatedState
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.input.pointer.AwaitPointerEventScope
+import androidx.compose.ui.input.pointer.PointerEvent
+import androidx.compose.ui.input.pointer.PointerEventType
+import androidx.compose.ui.input.pointer.pointerInput
+import androidx.compose.ui.unit.Density
 import androidx.compose.ui.unit.dp
+import androidx.compose.ui.util.fastFold
 import com.hippo.ehviewer.Settings
 import com.hippo.ehviewer.collectAsState
 import com.hippo.ehviewer.gallery.PageLoader2
@@ -22,6 +29,9 @@ import eu.kanade.tachiyomi.ui.reader.setting.ReadingModeType.RIGHT_TO_LEFT
 import eu.kanade.tachiyomi.ui.reader.setting.ReadingModeType.VERTICAL
 import eu.kanade.tachiyomi.ui.reader.setting.TappingInvertMode
 import eu.kanade.tachiyomi.ui.reader.viewer.ViewerNavigation
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.flow.collectLatest
+import kotlinx.coroutines.flow.receiveAsFlow
 
 @Composable
 fun GalleryPager(
@@ -58,6 +68,14 @@ fun GalleryPager(
     }
     val navigator by rememberUpdatedState(regions)
     if (isPagerType) {
+        val channel = remember { Channel<Float>(Channel.CONFLATED) }
+        LaunchedEffect(channel) {
+            channel.receiveAsFlow().collectLatest { delta ->
+                if (delta != 0f) {
+                    if (delta < 0) pagerState.moveToNext() else pagerState.moveToPrevious()
+                }
+            }
+        }
         PagerViewer(
             pagerState = pagerState,
             isRtl = type == RIGHT_TO_LEFT,
@@ -67,7 +85,15 @@ fun GalleryPager(
             onSelectPage = onSelectPage,
             onMenuRegionClick = onMenuRegionClick,
             contentPadding = contentPadding,
-            modifier = modifier,
+            modifier = modifier.pointerInput(channel) {
+                awaitPointerEventScope {
+                    while (true) {
+                        val event = awaitScrollEvent()
+                        val delta = calculateMouseWheelScroll(event)
+                        channel.trySend(delta)
+                    }
+                }
+            },
         )
     } else {
         WebtoonViewer(
@@ -83,3 +109,16 @@ fun GalleryPager(
     }
     NavigationOverlay(showNavigationOverlay, regions, modifier = Modifier.fillMaxSize())
 }
+
+private suspend fun AwaitPointerEventScope.awaitScrollEvent(): PointerEvent {
+    var event: PointerEvent
+    do {
+        event = awaitPointerEvent()
+    } while (event.type != PointerEventType.Scroll)
+    return event
+}
+
+private fun Density.calculateMouseWheelScroll(event: PointerEvent): Float {
+    // 64 dp value is taken from ViewConfiguration.java, replace with better solution
+    return event.changes.fastFold(0f) { acc, c -> acc + c.scrollDelta.y } * -64.dp.toPx()
+}