ENH: consider colors with de < 5 as the same

1. Use cie de2000 as color distance
2.Consider colors with de < 5 as the same color  when calculating
flush

jira:NONE

Signed-off-by: xun.zhang <xun.zhang@bambulab.com>
Change-Id: I4b451910a21c9db3471c63c270f1f120e3c5d160
(cherry picked from commit 72bc6f44cfab9145aecdb843ac4a03a9338a8cc6)

src/libslic3r/FlushVolPredictor.hpp

@@ -3,20 +3,56 @@
 
 #include<unordered_map>
 
+namespace FlushPredict
+{
+    struct RGBColor
+    {
+        unsigned char r{ 0 };
+        unsigned char g{ 0 };
+        unsigned char b{ 0 };
+        RGBColor(unsigned char r_,unsigned char g_,unsigned char b_) :r(r_),g(g_),b(b_){}
+        RGBColor() = default;
+    };
+
+    struct LABColor
+    {
+        double l{ 0 };
+        double a{ 0 };
+        double b{ 0 };
+        LABColor() = default;
+        LABColor(double l_,double a_,double b_):l(l_),a(a_),b(b_){}
+    };
+    // transfer colour in RGB space to LAB space
+    LABColor RGB2LAB(const RGBColor& color);
+    // calculate DeltaE2000
+    float calc_color_distance(const LABColor& lab1, const LABColor& lab2);
+    float calc_color_distance(const RGBColor& rgb1, const RGBColor& rgb2);
+    // check if DeltaE is within the threshold. We consider colors within the threshold to be the same
+    bool is_similar_color(const RGBColor& from, const RGBColor& to, float distance_threshold = 5.0);
+
+}
+
+
+// Singleton pattern
 class FlushVolPredictor
 {
+    using RGB = FlushPredict::RGBColor;
 public:
-    bool predict(const unsigned char src_r, const unsigned char src_g, const unsigned char src_b,
-        const unsigned char dst_r, const unsigned char dst_g, const unsigned char dst_b, float& flush);
+    bool predict(const RGB& from,const RGB& to , float& flush);
     static FlushVolPredictor& get_instance();
 private:
     FlushVolPredictor(const std::string& data_file);
     FlushVolPredictor(const FlushVolPredictor&) = delete;
     FlushVolPredictor& operator=(const FlushVolPredictor&) = delete;
     ~FlushVolPredictor() = default;
+
+    uint64_t generate_hash_key(const RGB& from, const RGB& to);
 private:
     std::unordered_map<uint64_t, float> m_flush_map;
+    std::vector<RGB> m_colors;
     bool m_valid;
 };
 
+
+
 #endif