app/src/main/java/de/jeanlucmakiola/calendula/ui/common/CalendarTransitions.kt

@@ -1,6 +1,7 @@
 package de.jeanlucmakiola.calendula.ui.common
 
 import androidx.compose.animation.ContentTransform
+import androidx.compose.animation.SizeTransform
 import androidx.compose.animation.core.FiniteAnimationSpec
 import androidx.compose.animation.fadeIn
 import androidx.compose.animation.fadeOut
@@ -23,9 +24,13 @@ import androidx.compose.ui.unit.IntOffset
  */
 
 /**
- * The M3 Expressive spatial spring used for the month/week slide: the *fast*
- * spring-physics spec from the active motion scheme — snappy with a subtle
- * springy settle, rather than a fixed easing curve.
+ * The M3 Expressive spatial spring used for the month/week/day slide: the
+ * *default* spring-physics spec from the active motion scheme, rather than a
+ * fixed easing curve.
+ *
+ * Default rather than fast: `fastSpatialSpec` is tuned for small, incidental
+ * movement, and driving a whole calendar page with it made the settle read as a
+ * twitch instead of a glide.
  *
  * Read it in a composable scope (this helper) so it can be captured by the
  * non-composable `AnimatedContent` transitionSpec lambda.
@@ -33,27 +38,34 @@ import androidx.compose.ui.unit.IntOffset
 @OptIn(ExperimentalMaterial3ExpressiveApi::class)
 @Composable
 fun rememberCalendarSlideSpec(): FiniteAnimationSpec<IntOffset> =
-    MaterialTheme.motionScheme.fastSpatialSpec()
+    MaterialTheme.motionScheme.defaultSpatialSpec()
 
 /**
- * The fast effects spec from the active motion scheme, for opacity (fade)
- * transitions. Captured in composable scope alongside [rememberCalendarSlideSpec]
- * for use in non-composable transition lambdas and as the reduced-motion fallback.
+ * The effects spec from the active motion scheme, for the opacity half of the
+ * transition. Captured in composable scope alongside [rememberCalendarSlideSpec]
+ * for use in non-composable transition lambdas, and reused on its own as the
+ * reduced-motion fallback.
+ *
+ * Opacity gets its own spec on purpose: M3 Expressive springs *position* and
+ * eases *opacity*, and a fade that bounced with the slide would shimmer.
  */
 @OptIn(ExperimentalMaterial3ExpressiveApi::class)
 @Composable
 fun rememberCalendarFadeSpec(): FiniteAnimationSpec<Float> =
-    MaterialTheme.motionScheme.fastEffectsSpec()
+    MaterialTheme.motionScheme.defaultEffectsSpec()
 
 /**
- * Horizontal slide for navigating between adjacent months/weeks/days.
+ * Navigating between adjacent months/weeks/days, as M3's shared-axis X: the
+ * outgoing page slides and fades one way while the incoming one arrives from the
+ * other, position on a spring and opacity on an easing curve.
  *
  * @param slideDir     +1 = forward (incoming from the right), -1 = back, 0 = jump
  *                     (e.g. "today"); a jump reuses the forward direction.
  * @param spec         spatial animation spec, typically [rememberCalendarSlideSpec].
- * @param fadeSpec     effects spec for the reduced-motion fade, typically
+ * @param fadeSpec     effects spec for the opacity half, and for the whole
+ *                     transition under reduced motion; typically
  *                     [rememberCalendarFadeSpec].
- * @param reduceMotion when true, swap the directional slide for a plain cross-fade.
+ * @param reduceMotion when true, drop the movement and cross-fade alone.
  */
 fun calendarSlideTransition(
     slideDir: Int,
@@ -65,6 +77,26 @@ fun calendarSlideTransition(
         return fadeIn(fadeSpec).togetherWith(fadeOut(fadeSpec))
     }
     val dir = if (slideDir == 0) 1 else slideDir
-    return slideInHorizontally(spec) { w -> dir * w }
-        .togetherWith(slideOutHorizontally(spec) { w -> -dir * w })
+    return ContentTransform(
+        targetContentEnter =
+            slideInHorizontally(spec) { w -> dir * w / SLIDE_TRAVEL_DIVISOR } + fadeIn(fadeSpec),
+        initialContentExit =
+            slideOutHorizontally(spec) { w -> -dir * w / SLIDE_TRAVEL_DIVISOR } + fadeOut(fadeSpec),
+        // AnimatedContent clips to the animating container by default, which
+        // shears the pages against the viewport edge as they pass. There is no
+        // size change here to contain — both pages are the same grid.
+        sizeTransform = SizeTransform(clip = false),
+    )
 }
+
+/**
+ * How far a page travels, as a fraction of the container width.
+ *
+ * A full width was the obvious reading of "paging", but the two pages are
+ * stacked and both opaque, so a full-width slide showed one grid racing across
+ * another — the movement carried the whole transition and had a long way to go.
+ * Under M3's shared-axis pattern the offset only has to *hint* the direction
+ * while the cross-fade does the swapping, so a fifth of the width is plenty and
+ * leaves nothing skating past.
+ */
+private const val SLIDE_TRAVEL_DIVISOR = 5

app/src/main/java/de/jeanlucmakiola/calendula/ui/month/MonthScreen.kt

@@ -777,15 +777,20 @@ internal fun DenseMonthGrid(
 
 /**
  * The month-changing horizontal swipe, shared by the paged and split styles.
- * Accumulates the drag and commits past a small threshold on release — the grid
+ * Accumulates the drag and commits past a threshold on release — the grid
  * doesn't follow the finger, so there is no distance to rubber-band against.
+ *
+ * The threshold matches the week and day views'. It used to be 6dp, which is
+ * inside the distance a tap wanders: brushing the grid changed the month, and a
+ * page that turns on an unintended gesture reads as the animation misfiring
+ * rather than as the gesture being over-eager.
  */
 @Composable
 private fun rememberMonthSwipeModifier(
     onSwipeNext: () -> Unit,
     onSwipePrev: () -> Unit,
 ): Modifier {
-    val threshold = with(LocalDensity.current) { 6.dp.toPx() }
+    val threshold = with(LocalDensity.current) { MONTH_SWIPE_THRESHOLD.toPx() }
     var dragAccum by remember { mutableFloatStateOf(0f) }
     return Modifier.pointerInput(Unit) {
         detectHorizontalDragGestures(
@@ -803,6 +808,9 @@ private fun rememberMonthSwipeModifier(
     }
 }
 
+/** Drag distance that commits a month change, matching the week and day views. */
+private val MONTH_SWIPE_THRESHOLD = 24.dp
+
 /**
  * Split style content: the compact grid keeps the month swipe, the pane below it
  * lists whatever day is selected.