Persist zoom, pan state across config changes

Author: jayasuryat

minesweeper-ui/build.gradle.kts

@@ -1,6 +1,7 @@
 plugins {
     id("com.android.library")
     kotlin("android")
+    id("kotlin-parcelize")
 }
 
 android {

minesweeper-ui/src/main/java/com/jayasuryat/minesweeperui/component/ZoomableContent.kt

@@ -22,19 +22,20 @@ import androidx.compose.runtime.Stable
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.graphics.graphicsLayer
 import androidx.compose.ui.input.pointer.pointerInput
+import com.jayasuryat.minesweeperui.grid.ZoomPanState
 import kotlin.math.absoluteValue
 
 @Composable
 internal fun ZoomableContent(
     modifier: Modifier = Modifier,
-    content: @Composable (zoomModifier: Modifier) -> Unit,
+    defaultState: ZoomPanState,
+    content: @Composable (zoomPanState: ZoomPanState) -> Unit,
 ) {
 
-    val scale = remember { mutableStateOf(1f) }
-    val translateX = remember { mutableStateOf(0f) }
-    val translateY = remember { mutableStateOf(0f) }
+    val scale = remember { mutableStateOf(defaultState.scale) }
+    val translateX = remember { mutableStateOf(defaultState.translationX) }
+    val translateY = remember { mutableStateOf(defaultState.translationY) }
 
     Box(
         modifier = modifier
@@ -68,13 +69,11 @@ internal fun ZoomableContent(
     ) {
 
         content(
-            zoomModifier = Modifier
-                .graphicsLayer(
-                    scaleX = scale.value,
-                    scaleY = scale.value,
-                    translationX = translateX.value,
-                    translationY = translateY.value,
-                )
+            ZoomPanState(
+                scale = scale.value,
+                translationX = translateX.value,
+                translationY = translateY.value,
+            )
         )
     }
 }

minesweeper-ui/src/main/java/com/jayasuryat/minesweeperui/grid/Minefield.kt

@@ -16,7 +16,11 @@
 package com.jayasuryat.minesweeperui.grid
 
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.saveable.rememberSaveable
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.graphicsLayer
 import com.jayasuryat.minesweeperui.action.CellInteractionListener
 import com.jayasuryat.minesweeperui.component.ZoomableContent
 import com.jayasuryat.util.LogCompositions
@@ -30,10 +34,30 @@ public fun Minefield(
 
     LogCompositions(name = "Minefield")
 
-    ZoomableContent { zoomModifier: Modifier ->
+    val savableState = rememberSaveable {
+        mutableStateOf(
+            ZoomPanState(
+                scale = 1f,
+                translationX = 0f,
+                translationY = 0f,
+            )
+        )
+    }
+    val zoomPanState = remember { savableState.value }
+
+    ZoomableContent(
+        defaultState = zoomPanState,
+    ) { zoomState: ZoomPanState ->
+
+        savableState.value = zoomState
 
         MineGrid(
-            modifier = modifier.then(zoomModifier),
+            modifier = modifier.then(Modifier.graphicsLayer {
+                scaleX = zoomState.scale
+                scaleY = zoomState.scale
+                translationX = zoomState.translationX
+                translationY = zoomState.translationY
+            }),
             gridInfo = gridInfo,
             actionListener = actionListener,
         )

minesweeper-ui/src/main/java/com/jayasuryat/minesweeperui/grid/ZoomPanState.kt

@@ -0,0 +1,13 @@
+package com.jayasuryat.minesweeperui.grid
+
+import android.os.Parcelable
+import androidx.compose.runtime.Immutable
+import kotlinx.parcelize.Parcelize
+
+@Parcelize
+@Immutable
+internal data class ZoomPanState(
+    val scale: Float,
+    val translationX: Float,
+    val translationY: Float,
+) : Parcelable