implement heightmap grid

engine/node_panel_grid.h

@@ -5,6 +5,10 @@
 #include "brush.h"
 #include "node_checkbox.h"
 #include "node_combobox.h"
+#include "node_image_texture.h"
+#include "node_button.h"
+#include "shape.h"
+#include "image.h"
 
 class NodePanelGrid : public Node
 {
@@ -17,7 +21,13 @@ public:
     NodeSliderH* m_box_width;
     NodeSliderH* m_box_height;
     NodeSliderH* m_box_depth;
-    
+    NodeImageTexture* m_hm_preview;
+    NodeButton* m_hm_load;
+    NodeSliderH* m_hm_offset;
+    NodeSliderH* m_hm_height;
+    ui::HeightmapPlane m_hm_plane;
+    ui::Image m_hm_image;
+
     virtual Node* clone_instantiate() const override;
     virtual void clone_finalize(Node* dest) const override;
     virtual void init() override;