add support for high res brush textures, implement mipmaps on brush

engine/node_panel_brush.h

@@ -8,6 +8,8 @@ class NodeButtonBrush : public NodeButtonCustom
 public:
     int m_brushID;
     bool m_selected = false;
+    std::string high_path;
+    uint16_t high_id;
     NodeImage* img;
     virtual Node* clone_instantiate() const override;
     virtual void init() override;
@@ -27,5 +29,6 @@ public:
     void handle_click(Node* target);
     std::vector<std::string> FindAllBrushes(const std::string& folder);
     uint16_t get_texture_id(int index) const;
-    void set_texture_id(int texid);
+    int get_brush_id(int index) const;
+    void select_brush(int brush_id);
 };