SDLPP: add texture flipping/rotation

sdlpp/sdlpp_renderobject.hpp

@@ -8,6 +8,7 @@
 #include "sdlpp_vector.hpp"
 #include "sdlpp_visitor.hpp"
 
+#include <SDL2/SDL_render.h>
 #include <memory>
 #include <vector>
 
@@ -111,6 +112,11 @@ public:
     void animate( int ticks );
     void visit( Visitor &visitor );
     void setAlignment( ObjectAlignment horizontal, ObjectAlignment vertical );
+    void flipHorizontally();
+    void flipVertically();
+    void setRotationCenter( const Vec2D< double > &center );
+    void rotateClockwise( int angle );
+    void rotateCounterClockwise( int angle );
 
 protected:
     virtual void copyTo( std::shared_ptr< RenderObject > other );
@@ -140,6 +146,10 @@ protected:
     int animation_next_frame_base = 0;
     std::vector< SDL_Rect > animation{};
     bool animating = true;
+    SDL_RendererFlip flip = SDL_FLIP_NONE;
+    Vec2D< double > rotation_center = { -1, -1 };
+    SDL_Point rotation_center_point;
+    int rotation_angle = 0;
 
 private:
     friend Scene;