Share video zoom geometry between Android viewers

tools/chatgui-android/app/src/main/java/com/utun/chat/ui/screens/VideoPlayerScreen.kt

@@ -36,7 +36,7 @@ import androidx.compose.material3.Text
 import androidx.compose.runtime.*
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.geometry.Size
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.graphics.graphicsLayer
 import androidx.compose.ui.input.pointer.pointerInput
@@ -67,12 +67,6 @@ private tailrec fun Context.findActivity(): Activity? = when (this) {
     else -> null
 }
 
-private fun clampOffset(scale: Float, o: Offset, vW: Float, vH: Float, sW: Float, sH: Float): Offset {
-    val mx = ((vW * scale - sW) / 2f).coerceAtLeast(0f)
-    val my = ((vH * scale - sH) / 2f).coerceAtLeast(0f)
-    return Offset(o.x.coerceIn(-mx, mx), o.y.coerceIn(-my, my))
-}
-
 @Composable
 fun VideoPlayerScreen(filePath: String, onClose: () -> Unit) {
     val player = remember(filePath) { MediaPlayer() }
@@ -88,8 +82,7 @@ fun VideoPlayerScreen(filePath: String, onClose: () -> Unit) {
     var dragPosition by remember { mutableStateOf(0) }
     var wasPlayingBeforeDrag by remember { mutableStateOf(false) }
     var videoInfo by remember { mutableStateOf<VideoInfo?>(null) }
-    var zoomScale by remember(filePath) { mutableStateOf(1f) }
-    var zoomOffset by remember(filePath) { mutableStateOf(Offset.Zero) }
+    val zoom = remember(filePath) { VideoZoomState() }
     var hideTick by remember { mutableStateOf(0) }
 
     val context = LocalContext.current
@@ -290,8 +283,8 @@ fun VideoPlayerScreen(filePath: String, onClose: () -> Unit) {
         val videoH = with(density) { h.toPx() }
 
         /* re-clamp zoom offset when screen size changes (e.g. flip 180) */
-        LaunchedEffect(screenW, screenH) {
-            zoomOffset = clampOffset(zoomScale, zoomOffset, videoW, videoH, screenW, screenH)
+        LaunchedEffect(screenW, screenH, videoW, videoH) {
+            zoom.constrain(Size(videoW, videoH), Size(screenW, screenH))
         }
 
         AndroidView(
@@ -317,10 +310,10 @@ fun VideoPlayerScreen(filePath: String, onClose: () -> Unit) {
                 }
             },
             modifier = videoModifier.graphicsLayer {
-                scaleX = zoomScale
-                scaleY = zoomScale
-                translationX = zoomOffset.x
-                translationY = zoomOffset.y
+                scaleX = zoom.scale
+                scaleY = zoom.scale
+                translationX = zoom.offset.x
+                translationY = zoom.offset.y
             }
         )
 
@@ -344,18 +337,9 @@ fun VideoPlayerScreen(filePath: String, onClose: () -> Unit) {
                         }
                     }
                     .pointerInput(screenW, screenH, videoW, videoH) {
-                        detectTransformGestures { centroid, pan, zoom, _ ->
+                        detectTransformGestures { centroid, pan, factor, _ ->
                             onInteraction()
-                            val old = zoomScale
-                            val new = (zoomScale * zoom).coerceIn(1f, 4f)
-                            val z = new / old
-                            val rel = centroid - Offset(screenW / 2f, screenH / 2f)
-                            val raw = Offset(
-                                zoomOffset.x * z + rel.x * (1f - z) + pan.x,
-                                zoomOffset.y * z + rel.y * (1f - z) + pan.y
-                            )
-                            zoomScale = new
-                            zoomOffset = clampOffset(new, raw, videoW, videoH, screenW, screenH)
+                            zoom.transform(centroid, pan, factor, Size(videoW, videoH), Size(screenW, screenH))
                         }
                     }
             )

tools/chatgui-android/app/src/main/java/com/utun/chat/ui/screens/VideoZoomState.kt

@@ -0,0 +1,30 @@
+package com.utun.chat.ui.screens
+
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.geometry.Size
+
+/** Общая геометрия увеличения для файла и live: точка под пальцами сохраняется, края ограничивают сдвиг. */
+internal class VideoZoomState {
+    var scale by mutableStateOf(1f)
+        private set
+    var offset by mutableStateOf(Offset.Zero)
+        private set
+
+    fun transform(centroid: Offset, pan: Offset, factor: Float, video: Size, viewport: Size) {
+        val next = (scale * factor).coerceIn(1f, 4f)
+        val ratio = next / scale
+        val relative = centroid - Offset(viewport.width / 2f, viewport.height / 2f)
+        offset = offset * ratio + relative * (1f - ratio) + pan
+        scale = next
+        constrain(video, viewport)
+    }
+
+    fun constrain(video: Size, viewport: Size) {
+        val x = ((video.width * scale - viewport.width) / 2f).coerceAtLeast(0f)
+        val y = ((video.height * scale - viewport.height) / 2f).coerceAtLeast(0f)
+        offset = Offset(offset.x.coerceIn(-x, x), offset.y.coerceIn(-y, y))
+    }
+}

tools/chatgui-android/app/src/test/java/com/utun/chat/ui/screens/VideoZoomStateTest.kt

@@ -0,0 +1,51 @@
+package com.utun.chat.ui.screens
+
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.geometry.Size
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class VideoZoomStateTest {
+    private val video = Size(1920f, 1080f)
+    private val viewport = Size(2400f, 1080f)
+    private val center = Offset(1200f, 540f)
+
+    @Test fun pinchKeepsPointUnderFingers() {
+        val zoom = VideoZoomState()
+        zoom.transform(center + Offset(100f, 50f), Offset.Zero, 2f, video, viewport)
+        assertEquals(2f, zoom.scale)
+        assertEquals(Offset(-100f, -50f), zoom.offset)
+    }
+
+    @Test fun panCannotExposeSpaceBeyondVideoEdges() {
+        val zoom = VideoZoomState()
+        zoom.transform(center, Offset(10000f, -10000f), 2f, video, viewport)
+        assertEquals(Offset(720f, -540f), zoom.offset)
+    }
+
+    @Test fun returningToOneCentersVideoAndPreventsDragging() {
+        val zoom = VideoZoomState()
+        zoom.transform(center, Offset(300f, 300f), 3f, video, viewport)
+        zoom.transform(center, Offset(100f, 100f), 0.1f, video, viewport)
+        assertEquals(1f, zoom.scale)
+        assertEquals(Offset.Zero, zoom.offset)
+    }
+
+    @Test fun zoomLimitUsesActualScaleForAnchoring() {
+        val zoom = VideoZoomState()
+        zoom.transform(center, Offset.Zero, 3f, video, viewport)
+        zoom.transform(center + Offset(300f, 0f), Offset.Zero, 2f, video, viewport)
+        assertEquals(4f, zoom.scale)
+        assertEquals(-100f, zoom.offset.x, 0.001f)
+    }
+
+    @Test fun changingVideoOrWindowSizeClampsExistingOffset() {
+        val zoom = VideoZoomState()
+        zoom.transform(center, Offset(700f, 500f), 2f, video, viewport)
+        zoom.constrain(Size(600f, 1080f), viewport)
+        assertEquals(Offset(0f, 500f), zoom.offset)
+        zoom.constrain(Size(1080f, 607.5f), Size(1080f, 2400f))
+        assertEquals(Offset.Zero, zoom.offset)
+        assertEquals(2f, zoom.scale)
+    }
+}