app: harden mirroring lifecycle and state

1 files changed, 34 insertions, 0 deletions

diff --git a/app/src/main/java/invalid/lena/scrcpy/TouchMap.java b/app/src/main/java/invalid/lena/scrcpy/TouchMap.java
new file mode 100644
index 0000000..d1289e0
--- /dev/null
+++ b/app/src/main/java/invalid/lena/scrcpy/TouchMap.java
@@ -0,0 +1,34 @@
+package invalid.lena.scrcpy;
+
+// Maps a coordinate in the activity window onto the target's pixels.
+//
+// Android-free for the same reason Wire and ControlMessages are: this is
+// the arithmetic that decides where a tap lands, and it is worth testing
+// without an emulator. Controller cannot be tested directly because it
+// takes MotionEvent.
+//
+// The video does not fill the window. It is letterboxed to the target's
+// aspect ratio and centred, so a coordinate has to have the bar
+// subtracted before it is scaled.
+public final class TouchMap {
+
+    private TouchMap() {}
+
+    // coord      - along one axis, in window coordinates
+    // viewOrigin - where the video rectangle starts on that axis
+    // viewSpan   - how long the video rectangle is on that axis
+    // targetSpan - the target's size on that axis
+    //
+    // Clamped into the rectangle rather than rejected: a drag that wanders
+    // onto a letterbox bar and is released there must still deliver its
+    // UP, or the target keeps the pointer down for the rest of the
+    // session. Returns 0..targetSpan-1.
+    public static int map(int coord, int viewOrigin, int viewSpan, int targetSpan) {
+        if (viewSpan <= 0 || targetSpan <= 0) return 0;
+        long v = (long) coord - viewOrigin;
+        if (v < 0) v = 0;
+        else if (v > viewSpan - 1) v = viewSpan - 1;
+        // 64-bit intermediate: a 4K target times a 4K span overflows int.
+        return (int) (v * targetSpan / viewSpan);
+    }
+}