Platform: implement AndroidApplication::MouseMoveEvent::relativePosition().

doc/changelog.dox

@@ -518,11 +518,12 @@ See also:
     [mosra/magnum#332](https://github.com/mosra/magnum/pull/332))
 -   @ref Platform::Sdl2Application::mainLoopIteration() now returns a
     @cpp bool @ce to indicate if the application should exit
--   @ref Platform::GlfwApplication and @ref Platform::EmscriptenApplication now
+-   @ref Platform::GlfwApplication, @ref Platform::EmscriptenApplication and
-    implement @ref Platform::GlfwApplication::MouseMoveEvent::relativePosition()
+    @ref Platform::AndroidApplication now implement
-    as well for better compatibility with @ref Platform::Sdl2Application. The
+    @ref Platform::GlfwApplication::MouseMoveEvent::relativePosition() as well
-    relative position is not supplied by the underlying toolkits, so it's
+    for better compatibility with @ref Platform::Sdl2Application. The relative
-    emulated on the application side.
+    position is not supplied by the underlying toolkits, so it's emulated on
+    the application side.
 -   Extended @ref Platform::BasicScreen with
     @ref Platform::BasicScreen::mouseScrollEvent() "mouseScrollEvent()",
     @ref Platform::BasicScreen::textInputEvent() "textInputEvent()" and

src/Magnum/Platform/AndroidApplication.cpp

@@ -250,13 +250,21 @@ std::int32_t AndroidApplication::inputEvent(android_app* state, AInputEvent* eve
         switch(action) {
             case AMOTION_EVENT_ACTION_DOWN:
             case AMOTION_EVENT_ACTION_UP: {
+                /* On a touch screen move events aren't reported when the
+                   finger is moving above (of course), so remember the position
+                   always */
+                app._previousMouseMovePosition = {Int(AMotionEvent_getX(event, 0)), Int(AMotionEvent_getY(event, 0))};
                 MouseEvent e(event);
                 action == AMOTION_EVENT_ACTION_DOWN ? app.mousePressEvent(e) : app.mouseReleaseEvent(e);
                 return e.isAccepted() ? 1 : 0;
             }
 
             case AMOTION_EVENT_ACTION_MOVE: {
-                MouseMoveEvent e(event);
+                Vector2i position{Int(AMotionEvent_getX(event, 0)), Int(AMotionEvent_getY(event, 0))};
+                MouseMoveEvent e{event,
+                    app._previousMouseMovePosition == Vector2i{-1} ? Vector2i{} :
+                    position - app._previousMouseMovePosition};
+                app._previousMouseMovePosition = position;
                 app.mouseMoveEvent(e);
                 return e.isAccepted() ? 1 : 0;
             }

src/Magnum/Platform/AndroidApplication.h

@@ -418,6 +418,7 @@ class AndroidApplication {
         EGLDisplay _display;
         EGLSurface _surface;
         EGLContext _glContext;
+        Vector2i _previousMouseMovePosition{-1};
 
         Containers::Pointer<Platform::GLContext> _context;
         Containers::Pointer<LogOutput> _logOutput;
@@ -765,6 +766,16 @@ class AndroidApplication::MouseMoveEvent: public InputEvent {
                     Int(AMotionEvent_getY(_event, 0))};
         }
 
+        /**
+         * @brief Relative position
+         *
+         * Position relative to previous move event. Unlike
+         * @ref Sdl2Application, Android APIs don't provide relative position
+         * directly, so this is calculated explicitly as a delta from previous
+         * move event position.
+         */
+        Vector2i relativePosition() const { return _relativePosition; }
+
         /** @brief Mouse buttons */
         Buttons buttons() const {
             #if __ANDROID_API__ >= 14
@@ -775,7 +786,9 @@ class AndroidApplication::MouseMoveEvent: public InputEvent {
         }
 
     private:
-        explicit MouseMoveEvent(AInputEvent* event): InputEvent(event) {}
+        explicit MouseMoveEvent(AInputEvent* event, Vector2i relativePosition): InputEvent{event}, _relativePosition{relativePosition} {}
+
+        const Vector2i _relativePosition;
 };
 
 CORRADE_ENUMSET_OPERATORS(AndroidApplication::MouseMoveEvent::Buttons)