Extract mouse processor trait

Mainly for consistency with the keyboard processor trait.

This could allow to provide alternative mouse processors.

app/src/trait/mouse_processor.h

@@ -0,0 +1,39 @@
+#ifndef SC_MOUSE_PROCESSOR_H
+#define SC_MOUSE_PROCESSOR_H
+
+#include "common.h"
+
+#include <assert.h>
+#include <stdbool.h>
+
+#include <SDL2/SDL_events.h>
+
+/**
+ * Mouse processor trait.
+ *
+ * Component able to process and inject mouse events should implement this
+ * trait.
+ */
+struct sc_mouse_processor {
+    const struct sc_mouse_processor_ops *ops;
+};
+
+struct sc_mouse_processor_ops {
+    void
+    (*process_mouse_motion)(struct sc_mouse_processor *mp,
+                            const SDL_MouseMotionEvent *event);
+
+    void
+    (*process_touch)(struct sc_mouse_processor *mp,
+                     const SDL_TouchFingerEvent *event);
+
+    void
+    (*process_mouse_button)(struct sc_mouse_processor *mp,
+                            const SDL_MouseButtonEvent *event);
+
+    void
+    (*process_mouse_wheel)(struct sc_mouse_processor *mp,
+                           const SDL_MouseWheelEvent *event);
+};
+
+#endif