add ZoomLevel and ZoomState

Author: SmartToolFactory

image/src/main/java/com/smarttoolfactory/image/zoom/ZoomLevel.kt

@@ -0,0 +1,10 @@
+package com.smarttoolfactory.image.zoom
+
+import androidx.compose.ui.Modifier
+
+/**
+ * Enum class for zoom levels to use with [Modifier.zoom]
+ */
+enum class ZoomLevel {
+    Initial, Min, Max
+}

image/src/main/java/com/smarttoolfactory/image/zoom/ZoomState.kt

@@ -0,0 +1,95 @@
+package com.smarttoolfactory.image.zoom
+
+import androidx.compose.animation.core.Animatable
+import androidx.compose.animation.core.VectorConverter
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
+import androidx.compose.ui.geometry.Offset
+import kotlinx.coroutines.coroutineScope
+
+@Composable
+fun rememberZoomState(
+    initialZoom: Float = 1f,
+    initialRotation: Float = 0f,
+    minZoom: Float = 1f,
+    maxZoom: Float = 5f
+): ZoomState {
+    return remember {
+        ZoomState(
+            initialZoom = initialZoom,
+            initialRotation = initialRotation,
+            minZoom = minZoom,
+            maxZoom = maxZoom
+        )
+    }
+}
+
+class ZoomState internal constructor(
+    initialZoom: Float = 1f,
+    initialRotation: Float = 0f,
+    minZoom: Float = 1f,
+    maxZoom: Float = 5f
+) {
+    internal var zoomLevel = ZoomLevel.Min
+
+    internal val zoomMin = minZoom.coerceAtLeast(.5f)
+    internal val zoomMax = maxZoom.coerceAtLeast(1f)
+    internal val zoomInitial = initialZoom.coerceIn(zoomMin, zoomMax)
+    internal val rotationInitial = initialRotation % 360
+
+    internal val animatablePan = Animatable(Offset.Zero, Offset.VectorConverter)
+    internal val animatableZoom = Animatable(zoomInitial)
+    internal val animatableRotation = Animatable(rotationInitial)
+
+    init {
+        require(zoomMax >= zoomMin)
+    }
+
+    val pan: Offset
+        get() = animatablePan.value
+
+    val zoom: Float
+        get() = animatableZoom.value
+
+    val rotation: Float
+        get() = animatableRotation.value
+
+    val zoomData: ZoomData
+        get() = ZoomData(
+            zoom = animatableZoom.value,
+            pan = animatablePan.value,
+            rotation = animatableRotation.value
+        )
+
+
+    fun boundPan(maxX: Float, maxY: Float) {
+        animatablePan.updateBounds(
+            Offset(-maxX, -maxY),
+            Offset(maxX, maxY)
+        )
+    }
+
+    suspend fun animatePanTo(pan: Offset) = coroutineScope {
+        animatablePan.animateTo(pan)
+    }
+
+    suspend fun animateZoomTo(zoom: Float) = coroutineScope {
+        animatableZoom.animateTo(zoom)
+    }
+
+    suspend fun animateRotationTo(rotation: Float) = coroutineScope {
+        animatableRotation.animateTo(rotation)
+    }
+
+    suspend fun snapPanTo(offset: Offset) = coroutineScope {
+        animatablePan.snapTo(offset)
+    }
+
+    suspend fun snapZoomTo(zoom: Float) = coroutineScope {
+        animatableZoom.snapTo(zoom)
+    }
+
+    suspend fun snapRotationTo(rotation: Float) = coroutineScope {
+        animatableRotation.snapTo(rotation)
+    }
+}

image/src/main/java/com/smarttoolfactory/image/zoom/ZoomUtil.kt

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+package com.smarttoolfactory.image.zoom
+
+fun calculateZoom(
+    zoomLevel: ZoomLevel,
+    initial: Float,
+    min: Float,
+    max: Float
+): Pair<ZoomLevel, Float> {
+
+    val newZoomLevel: ZoomLevel
+    val newZoom: Float
+
+    when (zoomLevel) {
+        ZoomLevel.Initial -> {
+            newZoomLevel = ZoomLevel.Max
+            newZoom = max
+        }
+        ZoomLevel.Max -> {
+            newZoomLevel = ZoomLevel.Min
+            newZoom = if(min == initial) (min +max)/2 else min
+        }
+        else -> {
+            newZoomLevel = ZoomLevel.Initial
+            newZoom = initial
+        }
+    }
+    return Pair(newZoomLevel, newZoom)
+}