From 2411416eb70ec73f93d679c80790aff88f2a4908 Mon Sep 17 00:00:00 2001
From: xfy <i@rua.plus>
Date: Fri, 15 May 2026 17:47:23 +0800
Subject: [PATCH] Add page fade-in/fade-out transition to CalendarPager and
 WeekPager

Use pagerState.currentPageOffsetFraction to compute alpha for page content:
alpha drops from 1 to 0 as offset goes from 0% to 30%, preventing
mid-point brightness dip (combined alpha of adjacent pages always >= 1f).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
---
 .../commonMain/kotlin/plus/rua/project/ui/CalendarPager.kt | 7 ++++++-
 .../src/commonMain/kotlin/plus/rua/project/ui/WeekPager.kt | 5 +++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/shared/src/commonMain/kotlin/plus/rua/project/ui/CalendarPager.kt b/shared/src/commonMain/kotlin/plus/rua/project/ui/CalendarPager.kt
index d8bc489..c7f2eab 100644
--- a/shared/src/commonMain/kotlin/plus/rua/project/ui/CalendarPager.kt
+++ b/shared/src/commonMain/kotlin/plus/rua/project/ui/CalendarPager.kt
@@ -9,10 +9,12 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.runtime.snapshotFlow
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.alpha
 import kotlinx.coroutines.flow.drop
 import kotlinx.coroutines.launch
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.number
+import kotlin.math.abs
 
 /**
  * 月度日历分页器，HorizontalPager 实现无限左右滑动切换月份。
@@ -63,6 +65,8 @@ fun CalendarPager(
         flingBehavior = PagerDefaults.flingBehavior(state = pagerState),
         modifier = modifier
     ) { page ->
+        val pageOffset = abs(pagerState.currentPageOffsetFraction)
+        val alpha = 1f - pageOffset.coerceIn(0f, 0.3f) / 0.3f
         val (year, month) = pageToYearMonth(page, initialYear, initialMonth)
         CalendarMonthPage(
             year = year,
@@ -87,7 +91,8 @@ fun CalendarPager(
             collapseProgress = collapseProgress,
             rowHeightPx = rowHeightPx,
             effectiveWeeks = effectiveWeeks,
-            onRowHeightMeasured = onRowHeightMeasured
+            onRowHeightMeasured = onRowHeightMeasured,
+            modifier = Modifier.alpha(alpha)
         )
     }
 }
\ No newline at end of file
diff --git a/shared/src/commonMain/kotlin/plus/rua/project/ui/WeekPager.kt b/shared/src/commonMain/kotlin/plus/rua/project/ui/WeekPager.kt
index e424b75..010a968 100644
--- a/shared/src/commonMain/kotlin/plus/rua/project/ui/WeekPager.kt
+++ b/shared/src/commonMain/kotlin/plus/rua/project/ui/WeekPager.kt
@@ -11,7 +11,9 @@ import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.snapshotFlow
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.alpha
 import androidx.compose.ui.unit.dp
+import kotlin.math.abs
 import kotlinx.coroutines.flow.drop
 import kotlinx.datetime.DatePeriod
 import kotlinx.datetime.LocalDate
@@ -53,9 +55,12 @@ fun WeekPager(
         flingBehavior = PagerDefaults.flingBehavior(state = pagerState),
         modifier = modifier
     ) { page ->
+        val pageOffset = abs(pagerState.currentPageOffsetFraction)
+        val alpha = 1f - pageOffset.coerceIn(0f, 0.3f) / 0.3f
         val weekMonday = pageToWeekMonday(page, initialWeekMonday)
         Row(
             modifier = Modifier
+                .alpha(alpha)
                 .fillMaxWidth()
                 .padding(vertical = ROW_PADDING_DP.dp)
         ) {