opentrack: fix desktop icon & window title

Patch fixes `app_id` under Wayland for runtime desktop icon. Previously
`WAYLAND_DEBUG=client opentrack |& grep app_id` would show `""`

New `cmakeFlags` provides `OPENTRACK_COMMIT`, which is usually detected
via `git describe`.

pkgs/by-name/op/opentrack/desktop-filename.patch

@@ -0,0 +1,15 @@
+diff --git a/gui/init.cpp b/gui/init.cpp
+index 1647b050db0efe76028000939a7ca8e4047116b7..9114c31c51a69294e0803c15008a824e18da7a09 100644
+--- a/gui/init.cpp
++++ b/gui/init.cpp
+@@ -315,6 +315,10 @@ int otr_main(int argc, char** argv, std::function<std::unique_ptr<QWidget>()> co
+     add_win32_path();
+ #endif
+ 
++#ifdef Q_OS_LINUX
++    app.setDesktopFileName("opentrack");
++#endif
++
+     QDir::setCurrent(OPENTRACK_BASE_PATH);
+ 
+     set_qt_style();

pkgs/by-name/op/opentrack/package.nix

@@ -40,6 +40,11 @@ stdenv.mkDerivation (finalAttrs: {
     meta.license = lib.licenses.free;
   };
 
+  patches = [
+    # calls `app.setDesktopFileName("opentrack");` - distros that don't wrap the binary apparently don't need this.
+    ./desktop-filename.patch
+  ];
+
   strictDeps = true;
 
   nativeBuildInputs = [
@@ -64,13 +69,14 @@ stdenv.mkDerivation (finalAttrs: {
   ];
 
   cmakeFlags = [
+    (lib.cmakeFeature "OPENTRACK_COMMIT" "opentrack-${finalAttrs.version}")
     (lib.cmakeBool "SDK_WINE" withWine)
     (lib.cmakeFeature "SDK_ARUCO_LIBPATH" "${finalAttrs.aruco}/lib/libaruco.a")
     (lib.cmakeFeature "SDK_XPLANE" finalAttrs.xplaneSdk.outPath)
   ];
 
   postInstall = ''
-    install -Dt $out/share/icons/hicolor/256x256 $src/gui/images/opentrack.png
+    install -Dt $out/share/icons/hicolor/256x256/apps ../gui/images/opentrack.png
   '';
 
   # manually wrap just the main binary