remove direct use of rtt and dirty area from the layer

src/canvas.h

@@ -127,13 +127,13 @@ public:
     Texture2D m_tex2[6];
     RTT m_merge_rtt;
     Texture2D m_merge_tex;
-    bool m_pick_ready[6];
+    bool m_pick_ready[6] = SIXPLETTE(false);
     std::unique_ptr<glm::u8vec4[]> m_pick_data[6] = SIXPLETTE(nullptr);
     static glm::vec3 m_plane_origin[6];
     static glm::vec3 m_plane_normal[6];
     static glm::vec3 m_plane_tangent[6];
     static glm::mat4 m_plane_transform[6];
-    glm::vec2 m_pattern_offset;
+    glm::vec2 m_pattern_offset{ 0 };
     Sampler m_sampler;
     Sampler m_sampler_nearest;
     Sampler m_sampler_linear;
@@ -145,7 +145,7 @@ public:
     float m_cam_fov = 85.f;
     const float m_cam_fov_min = 5.f;
     const float m_cam_fov_max = 150.f;
-    glm::vec2 m_cur_pos;
+    glm::vec2 m_cur_pos{ 0 };
 
     std::shared_ptr<Brush> m_current_brush;