Bezier curve gradient

include/ImNodeFlow.h

@@ -34,6 +34,17 @@ namespace ImFlow
      */
     inline static void smart_bezier(const ImVec2& p1, const ImVec2& p2, ImU32 color, float thickness);
 
+    /**
+     * @brief <BR>Draw a sensible bezier whose color blends from one end to the other
+     * @param p1 Starting point
+     * @param p2 Ending point
+     * @param color1 Color at the starting point
+     * @param color2 Color at the ending point
+     * @param thickness Thickness of the curve
+     * @param blend Tightness of the color transition. 1 = linear, >1 concentrates it toward the middle, <1 spreads it
+     */
+    inline static void smart_bezier_gradient(const ImVec2& p1, const ImVec2& p2, ImU32 color1, ImU32 color2, float thickness, float blend = 1.f);
+
     /**
      * @brief <BR>Collider checker for smart_bezier
      * @details Projects the point "p" orthogonally onto the bezier curve and
@@ -261,6 +272,8 @@ namespace ImFlow
         float grid_size = 50.f;
         /// @brief Sub-grid divisions for Node snapping
         float grid_subdivisions = 5.f;
+        /// @brief Tightness of gradient links. 1 = linear, >1 concentrates the color transition toward the middle, <1 spreads it out
+        float link_gradient_blend = 1.f;
         /// @brief ImNodeFlow colors
         InfColors colors;
     };

src/ImNodeFlow.cpp

@@ -25,7 +25,8 @@ namespace ImFlow {
         if (m_selected)
             smart_bezier(start, end, m_left->getStyle()->extra.outline_color,
                          thickness + m_left->getStyle()->extra.link_selected_outline_thickness);
-        smart_bezier(start, end, m_left->getStyle()->color, thickness);
+        smart_bezier_gradient(start, end, m_left->getStyle()->color, m_right->getStyle()->color, thickness,
+                              m_inf->getStyle().link_gradient_blend);
 
         if (m_selected && ImGui::IsKeyPressed(ImGuiKey_Delete, false))
             m_right->deleteLink();

src/ImNodeFlow.inl

@@ -18,6 +18,43 @@ namespace ImFlow
         dl->AddBezierCubic(p1, p11, p22, p2, color, thickness);
     }
 
+    inline void smart_bezier_gradient(const ImVec2& p1, const ImVec2& p2, ImU32 color1, ImU32 color2, float thickness, float blend)
+    {
+        if (color1 == color2)
+        {
+            smart_bezier(p1, p2, color1, thickness);
+            return;
+        }
+
+        ImDrawList* dl = ImGui::GetWindowDrawList();
+        float distance = sqrt(pow((p2.x - p1.x), 2.f) + pow((p2.y - p1.y), 2.f));
+        float delta = distance * 0.45f;
+        if (p2.x < p1.x) delta += 0.2f * (p1.x - p2.x);
+        float vert = 0.f;
+        ImVec2 p22 = p2 - ImVec2(delta, vert);
+        if (p2.x < p1.x - 50.f) delta *= -1.f;
+        ImVec2 p11 = p1 + ImVec2(delta, vert);
+
+        const int segments = 32;
+        ImVec4 c1 = ImGui::ColorConvertU32ToFloat4(color1);
+        ImVec4 c2 = ImGui::ColorConvertU32ToFloat4(color2);
+        ImVec2 prev = p1;
+        for (int i = 1; i <= segments; ++i)
+        {
+            float t = (float)i / (float)segments;
+            float u = 1.f - t;
+            ImVec2 pt(u*u*u*p1.x + 3*u*u*t*p11.x + 3*u*t*t*p22.x + t*t*t*p2.x,
+                      u*u*u*p1.y + 3*u*u*t*p11.y + 3*u*t*t*p22.y + t*t*t*p2.y);
+            float tm = ((float)i - 0.5f) / (float)segments;
+            if (blend != 1.f) // symmetric contrast curve around the midpoint
+                tm = (tm < 0.5f) ? 0.5f * powf(2.f * tm, blend)
+                                 : 1.f - 0.5f * powf(2.f * (1.f - tm), blend);
+            ImU32 col = ImGui::ColorConvertFloat4ToU32(ImLerp(c1, c2, tm));
+            dl->AddLine(prev, pt, col, thickness);
+            prev = pt;
+        }
+    }
+
     inline bool smart_bezier_collider(const ImVec2& p, const ImVec2& p1, const ImVec2& p2, float radius)
     {
         float distance = sqrt(pow((p2.x - p1.x), 2.f) + pow((p2.y - p1.y), 2.f));