[feat] add vertical pointer edge panning on mobile

apps/android/README.md

@@ -7,7 +7,7 @@
 - 官方或自托管 WSS 信令服务器；授权后进入前台即自动注册或登录本机身份，首页实时显示连接、重连及失败状态。发起桌面连接时复用该身份；切换服务器会重新登录，撤回授权会关闭连接。已有远程会话优先通过系统画中画保持连接，画中画不可用时由带连接通知的前台服务兜底；首页空闲信令在后台关闭。
 - 优先使用 MediaCodec 硬件解码 H.264 / AV1，硬件缓冲区直接提交 Surface；设备无对应硬件、分辨率超限或运行失败时，按原编码格式回退到 OpenH264 / dav1d。软件输出由独立显示线程将 NV12 转 RGBA；只保留最新待显示帧。MiniRTC 原有的通用压缩帧解码队列保持不变。
 - 48 kHz 单声道 PCM 播放，支持静音，音频队列有容量限制。
-- 相对鼠标（触控板）和绝对位置模式；单指点击、绝对模式按住拖动、长按右键，以及外接键盘、鼠标。画面手势与 iOS 一致：双指捏合以触点为中心缩放（1–10 倍），放大后双指拖动画面，原始比例下双指上下滑动控制滚轮。
+- 相对鼠标（触控板）和绝对位置模式；单指点击、绝对模式按住拖动、长按右键，以及外接键盘、鼠标。画面手势与 iOS 一致：双指捏合以触点为中心缩放（1–10 倍），放大后双指拖动画面，原始比例下双指上下滑动控制滚轮。相对鼠标移到可见画面的上、下边缘后继续向外移动，会反向上下平移画面，不触发左右平移；未放大时和按住虚拟鼠标键拖动时同样生效，停止移动即停止平移，抬手保留位置。移动到极限时，画面可见部分至少占当前显示区域高度的 20%，与缩放倍数无关；整幅画面高度不足该比例时完整保留，范围计入上下黑边；缩放结束及缩回 1 倍时保留平移位置，仅在超过可见边界时限制位置；切换显示器恢复居中。
 - 横竖屏等比例显示、远端多显示器切换。与 iOS 一致的画面质量（低/中/高）、采集帧率（30/60 fps）、画面偏好；支持能力检测、电脑端确认、失败/5 秒超时回退及连续操作的应答排序。
 - 根据常见移动设备解码能力和屏幕尺寸设置起始参数：显示长边不超过 1280 像素时默认低画质（最高 720p）/30 fps，其余默认中画质（最高 1080p）/30 fps。用户保存的画面偏好不变，仍可手动选择高画质或 60 fps。
 - 网络状态按视频、音频、数据、合计展示收发速率和丢包率，并显示实际提交帧率、分辨率、画面延时、平滑 RTT、P2P/TURN 和实际 SRTP 状态。每秒刷新，过期或无效测量显示“—”。

apps/android/app/src/main/java/cn/crossdesk/mobile/RemoteMouseInput.java

@@ -3,6 +3,8 @@ package cn.crossdesk.mobile;
 /** Shared button ownership and cursor position for the video surface and mouse bar. */
 final class RemoteMouseInput {
     interface Sender { void send(float x, float y, int flag, int wheel); }
+    interface RelativeMotion { void move(float dx, float dy); }
+    RelativeMotion relativeMotion;
     private final Sender sender;
     private float x = .5f, y = .5f;
     private boolean gestureLeft, virtualLeft, virtualRight;
@@ -19,7 +21,8 @@ final class RemoteMouseInput {
     }
     void drag(float dx, float dy) {
         if (!hasVirtualButton() || viewportWidth <= 0 || viewportHeight <= 0) return;
-        move(x + dx / viewportWidth, y + dy / viewportHeight);
+        if (relativeMotion != null) relativeMotion.move(dx, dy);
+        else move(x + dx / viewportWidth, y + dy / viewportHeight);
     }
     void gestureLeft(boolean down) {
         if (down && hasVirtualButton()) return;

apps/android/app/src/main/java/cn/crossdesk/mobile/RemoteVideoView.java

@@ -51,6 +51,7 @@ final class RemoteVideoView extends FrameLayout implements SurfaceHolder.Callbac
     RemoteVideoView(Context context, NativeSession session) {
         super(context); this.session = session;
         mouseInput = new RemoteMouseInput(this::sendMouse);
+        mouseInput.relativeMotion = this::moveRelative;
         setBackgroundColor(Color.BLACK);
         video = new SurfaceView(context); video.getHolder().addCallback(this);
         addView(video, new LayoutParams(1, 1, android.view.Gravity.CENTER));
@@ -147,14 +148,21 @@ final class RemoteVideoView extends FrameLayout implements SurfaceHolder.Callbac
         cursor.invalidate();
     }
     @Override protected void onSizeChanged(int w,int h,int oldw,int oldh) { post(this::fit); }
+    private void moveRelative(float dx, float dy) {
+        if (pictureInPicture || viewport.width() <= 0 || viewport.height() <= 0) return;
+        viewport.panForPointer(y, dy);
+        applyViewport();
+        mouseInput.move(x + dx / viewport.width(), y + dy / viewport.height());
+    }
     private boolean point(MotionEvent e) {
         boolean touchpad = relative && e.getToolType(0) != MotionEvent.TOOL_TYPE_MOUSE;
         float px=e.getX(),py=e.getY();
         if (!touchpad && !viewport.contains(px,py)) return false;
         if(touchpad){
             if(e.getActionMasked()==MotionEvent.ACTION_MOVE){
-                x=Math.max(0,Math.min(1,x+(px-lastX)/Math.max(1,viewport.width())));
-                y=Math.max(0,Math.min(1,y+(py-lastY)/Math.max(1,viewport.height())));
+                moveRelative(px-lastX,py-lastY);
+                lastX=px;lastY=py;
+                return true;
             }
         }else{
             x=viewport.normalizedX(px);

apps/android/app/src/main/java/cn/crossdesk/mobile/RemoteViewport.java

@@ -3,11 +3,14 @@ package cn.crossdesk.mobile;
 /** Geometry shared by the video Surface, cursor and remote pointer input. */
 final class RemoteViewport {
     private static final float MAXIMUM_SCALE = 10;
-    private int baseWidth, baseHeight, baseLeft, baseTop;
+    private static final float MINIMUM_VISIBLE_HEIGHT_FRACTION = .2f;
+    private int baseWidth, baseHeight, baseLeft, baseTop, containerHeight;
+    private boolean edgePanned;
     private float scale = 1, offsetX, offsetY;
 
     void fit(int width, int height, int videoWidth, int videoHeight) {
         if (width <= 0 || height <= 0 || videoWidth <= 0 || videoHeight <= 0) return;
+        containerHeight = height;
         double fitScale = Math.min((double) width / videoWidth, (double) height / videoHeight);
         baseWidth = Math.max(1, (int) (videoWidth * fitScale));
         baseHeight = Math.max(1, (int) (videoHeight * fitScale));
@@ -54,18 +57,46 @@ final class RemoteViewport {
         constrainOffset();
     }
 
-    void finishGesture() {
-        if (!isZoomed()) reset();
+    void panForPointer(float y, float dy) {
+        if (baseHeight == 0 || !Float.isFinite(dy)) return;
+        float overflowY = pointerOverflow(top() + y * height(), dy,
+            Math.max(0, top()), Math.min(containerHeight, top() + height()));
+        if (overflowY == 0) return;
+        edgePanned = true;
+        panBy(0, -overflowY);
     }
 
-    void reset() { scale = 1; offsetX = offsetY = 0; }
+    // Only the outward portion of this movement pans; an offscreen cursor must
+    // not make a tiny movement jump the viewport by its entire hidden distance.
+    private static float pointerOverflow(float position, float delta, float low, float high) {
+        if (delta > 0) return Math.min(delta, Math.max(0, position + delta - high));
+        if (delta < 0) return Math.max(delta, Math.min(0, position + delta - low));
+        return 0;
+    }
+
+    void finishGesture() {
+        if (!isZoomed()) {
+            scale = 1;
+            constrainOffset();
+        }
+    }
+
+    void reset() { scale = 1; offsetX = offsetY = 0; edgePanned = false; }
 
     private void constrainOffset() {
-        // Keep the original fitted area covered, as on iOS, even with letterboxing.
         float maximumX = baseWidth * (scale - 1) / 2;
-        float maximumY = baseHeight * (scale - 1) / 2;
+        float minimumY = -baseHeight * (scale - 1) / 2;
+        float maximumY = -minimumY;
+        if (edgePanned) {
+            // Reserve 20% of the viewport height regardless of zoom. If the
+            // whole image is shorter than that, keep its full height visible.
+            float visibleHeight = Math.min(height(), containerHeight * MINIMUM_VISIBLE_HEIGHT_FRACTION);
+            float centerY = baseTop + baseHeight / 2f;
+            minimumY = visibleHeight - centerY - height() / 2;
+            maximumY = containerHeight - visibleHeight - centerY + height() / 2;
+        }
         offsetX = clamp(offsetX, -maximumX, maximumX);
-        offsetY = clamp(offsetY, -maximumY, maximumY);
+        offsetY = clamp(offsetY, minimumY, maximumY);
     }
 
     private static float clamp(float value, float minimum, float maximum) {