Image: play with a ZoomableBox

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/components/ZoomableBox.kt

@@ -0,0 +1,106 @@
+/*
+ * Copyright (c) 2023 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.element.android.libraries.designsystem.components
+
+import androidx.compose.foundation.gestures.detectTapGestures
+import androidx.compose.foundation.gestures.detectTransformGestures
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.BoxScope
+import androidx.compose.foundation.layout.LayoutScopeMarker
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.Immutable
+import androidx.compose.runtime.Stable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.graphics.RectangleShape
+import androidx.compose.ui.graphics.graphicsLayer
+import androidx.compose.ui.input.pointer.pointerInput
+import androidx.compose.ui.layout.onSizeChanged
+import androidx.compose.ui.unit.IntSize
+
+@Composable
+fun ZoomableBox(
+    modifier: Modifier = Modifier,
+    minScale: Float = 1f,
+    maxScale: Float = 5f,
+    content: @Composable ZoomableBoxScope.() -> Unit
+) {
+    var scale by remember { mutableStateOf(1f) }
+    var offsetX by remember { mutableStateOf(0f) }
+    var offsetY by remember { mutableStateOf(0f) }
+    var size by remember { mutableStateOf(IntSize.Zero) }
+    Box(
+        modifier = modifier
+            .clip(RectangleShape)
+            .onSizeChanged { size = it }
+            .pointerInput(Unit) {
+                detectTransformGestures { _, pan, zoom, _ ->
+                    scale = maxOf(minScale, minOf(scale * zoom, maxScale))
+                    val maxX = (size.width * (scale - 1)) / 2
+                    val minX = -maxX
+                    offsetX = maxOf(minX, minOf(maxX, offsetX + pan.x))
+                    val maxY = (size.height * (scale - 1)) / 2
+                    val minY = -maxY
+                    offsetY = maxOf(minY, minOf(maxY, offsetY + pan.y))
+                }
+            }
+            .pointerInput(Unit) {
+                detectTapGestures(
+                    onDoubleTap = {
+                        offsetX = 0f
+                        offsetY = 0f
+                        scale = if (scale > minScale) {
+                            minScale
+                        } else {
+                            maxScale / 2f
+                        }
+
+                    }
+                )
+            }
+    ) {
+        DefaultZoomableBoxScope(this, scale, offsetX, offsetY).content()
+    }
+}
+
+@LayoutScopeMarker
+@Immutable
+interface ZoomableBoxScope : BoxScope {
+    @Stable
+    fun Modifier.zoomable(): Modifier
+}
+
+private class DefaultZoomableBoxScope(
+    private val parentScope: BoxScope,
+    private val scale: Float,
+    private val offsetX: Float,
+    private val offsetY: Float
+) : ZoomableBoxScope, BoxScope by parentScope {
+
+    override fun Modifier.zoomable(): Modifier {
+        return graphicsLayer(
+            scaleX = scale,
+            scaleY = scale,
+            translationX = offsetX,
+            translationY = offsetY
+        )
+    }
+}