Add observable progress

demo/src/main/kotlin/eu/wewox/pagecurl/MainActivity.kt

@@ -13,6 +13,7 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
@@ -29,8 +30,10 @@ import androidx.compose.ui.unit.sp
 import androidx.compose.ui.unit.toOffset
 import eu.wewox.pagecurl.components.SettingsAction
 import eu.wewox.pagecurl.components.SettingsPopup
+import eu.wewox.pagecurl.config.CurlConfig
 import eu.wewox.pagecurl.config.InteractionConfig
 import eu.wewox.pagecurl.config.PageCurlConfig
+import eu.wewox.pagecurl.config.ShadowConfig
 import eu.wewox.pagecurl.config.copy
 import eu.wewox.pagecurl.page.PageCurl
 import eu.wewox.pagecurl.page.PageCurlState
@@ -63,9 +66,23 @@ class MainActivity : ComponentActivity() {
                         )
                     }
 
+                    val curlConfig by derivedStateOf {
+                        val offset = if (state.progress > 0f) 0f else 1f
+                        val shadowAlpha = (offset + state.progress) * 0.5f
+
+                        CurlConfig(
+                            shadow = ShadowConfig(
+                                alpha = shadowAlpha
+                            )
+                        )
+                    }
+
                     PageCurl(
                         state = state,
-                        config = PageCurlConfig(interaction = interaction)
+                        config = PageCurlConfig(
+                            curl = curlConfig,
+                            interaction = interaction
+                        )
                     ) { index ->
                         Box(
                             modifier = Modifier

pagecurl/src/main/kotlin/eu/wewox/pagecurl/page/PageCurlState.kt

@@ -6,6 +6,7 @@ import androidx.compose.animation.core.TwoWayConverter
 import androidx.compose.animation.core.VisibilityThreshold
 import androidx.compose.animation.core.keyframes
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.saveable.Saver
@@ -53,6 +54,8 @@ public class PageCurlState(
     public var current: Int by mutableStateOf(initialCurrent)
         internal set
 
+    public val progress: Float get() = internalState?.progress ?: 0f
+
     internal var internalState: InternalState? by mutableStateOf(null)
 
     internal fun setup(constraints: Constraints) {
@@ -101,6 +104,16 @@ public class PageCurlState(
 
         var animateJob: Job? = null
 
+        val progress: Float by derivedStateOf {
+            if (forward.value != rightEdge) {
+                1f - forward.value.centerX / constraints.maxWidth
+            } else if (backward.value != leftEdge) {
+                -backward.value.centerX / constraints.maxWidth
+            } else {
+                0f
+            }
+        }
+
         suspend fun reset() {
             forward.snapTo(rightEdge)
             backward.snapTo(leftEdge)
@@ -134,6 +147,9 @@ public class PageCurlState(
 }
 
 public data class Edge(val top: Offset, val bottom: Offset) {
+
+    internal val centerX: Float = (top.x + bottom.x) * 0.5f
+
     internal companion object {
         val VectorConverter: TwoWayConverter<Edge, AnimationVector4D> =
             TwoWayConverter(