ImDrawList: Add AddNgon(), AddNgonFilled() API.

docs/CHANGELOG.txt

@@ -60,6 +60,10 @@ Other Changes:
 - Inputs: Added ImGuiMouseButton enum for convenience (e.g. ImGuiMouseButton_Right=1).
   We forever guarantee that the existing value will not changes so existing code is free to use 0/1/2.
 - Misc: Added ImGuiMouseCursor_NotAllowed enum so it can be used by more shared widgets. [@rokups]
+- ImDrawList: Add AddNgon(), AddNgonFilled() API with a guarantee on the explicit segment count.
+  In the current branch they are essentially the same as AddCircle(), AddCircleFilled() but as
+  we will rework the circle rendering functions to use textures and automatic segment count
+  selection, those new api can fill a gap. [@ShironekoBen]
 - Backends: GLFW, SDL, Win32, OSX, Allegro: Added support for ImGuiMouseCursor_NotAllowed. [@rokups]
 - Backends: GLFW: Added support for the missing mouse cursors newly added in GLFW 3.4+. [@rokups]
 - Examples: Explicitly adding -DIMGUI_IMPL_OPENGL_LOADER_GL3W to Makefile to match linking

imgui.h

@@ -1934,6 +1934,8 @@ struct ImDrawList
     IMGUI_API void  AddTriangleFilled(const ImVec2& p1, const ImVec2& p2, const ImVec2& p3, ImU32 col);
     IMGUI_API void  AddCircle(const ImVec2& center, float radius, ImU32 col, int num_segments = 12, float thickness = 1.0f);
     IMGUI_API void  AddCircleFilled(const ImVec2& center, float radius, ImU32 col, int num_segments = 12);
+    IMGUI_API void  AddNgon(const ImVec2& center, float radius, ImU32 col, int num_segments, float thickness = 1.0f);
+    IMGUI_API void  AddNgonFilled(const ImVec2& center, float radius, ImU32 col, int num_segments);
     IMGUI_API void  AddText(const ImVec2& pos, ImU32 col, const char* text_begin, const char* text_end = NULL);
     IMGUI_API void  AddText(const ImFont* font, float font_size, const ImVec2& pos, ImU32 col, const char* text_begin, const char* text_end = NULL, float wrap_width = 0.0f, const ImVec4* cpu_fine_clip_rect = NULL);
     IMGUI_API void  AddPolyline(const ImVec2* points, int num_points, ImU32 col, bool closed, float thickness);

imgui_demo.cpp

@@ -4440,9 +4440,11 @@ static void ShowExampleAppCustomRendering(bool* p_open)
         {
             static float sz = 36.0f;
             static float thickness = 3.0f;
+            static int ngon_sides = 6;
             static ImVec4 colf = ImVec4(1.0f, 1.0f, 0.4f, 1.0f);
             ImGui::DragFloat("Size", &sz, 0.2f, 2.0f, 72.0f, "%.0f");
             ImGui::DragFloat("Thickness", &thickness, 0.05f, 1.0f, 8.0f, "%.02f");
+            ImGui::SliderInt("n-gon sides", &ngon_sides, 3, 12);
             ImGui::ColorEdit4("Color", &colf.x);
             const ImVec2 p = ImGui::GetCursorScreenPos();
             const ImU32 col = ImColor(colf);
@@ -4455,7 +4457,7 @@ static void ShowExampleAppCustomRendering(bool* p_open)
             {
                 // First line uses a thickness of 1.0f, second line uses the configurable thickness
                 float th = (n == 0) ? 1.0f : thickness;
-                draw_list->AddCircle(ImVec2(x + sz*0.5f, y + sz*0.5f), sz*0.5f, col, 6, th);                x += sz + spacing;  // Hexagon
+                draw_list->AddNgon(ImVec2(x + sz*0.5f, y + sz*0.5f), sz*0.5f, col, ngon_sides, th);         x += sz + spacing;  // n-gon
                 draw_list->AddCircle(ImVec2(x + sz*0.5f, y + sz*0.5f), sz*0.5f, col, 20, th);               x += sz + spacing;  // Circle
                 draw_list->AddRect(ImVec2(x, y), ImVec2(x + sz, y + sz), col, 0.0f,  corners_none, th);     x += sz + spacing;  // Square
                 draw_list->AddRect(ImVec2(x, y), ImVec2(x + sz, y + sz), col, 10.0f, corners_all, th);      x += sz + spacing;  // Square with all rounded corners
@@ -4469,7 +4471,7 @@ static void ShowExampleAppCustomRendering(bool* p_open)
                 x = p.x + 4;
                 y += sz + spacing;
             }
-            draw_list->AddCircleFilled(ImVec2(x + sz*0.5f, y + sz*0.5f), sz*0.5f, col, 6);              x += sz + spacing;  // Hexagon
+            draw_list->AddNgonFilled(ImVec2(x + sz * 0.5f, y + sz * 0.5f), sz*0.5f, col, ngon_sides);   x += sz + spacing;  // n-gon
             draw_list->AddCircleFilled(ImVec2(x + sz*0.5f, y + sz*0.5f), sz*0.5f, col, 32);             x += sz + spacing;  // Circle
             draw_list->AddRectFilled(ImVec2(x, y), ImVec2(x + sz, y + sz), col);                        x += sz + spacing;  // Square
             draw_list->AddRectFilled(ImVec2(x, y), ImVec2(x + sz, y + sz), col, 10.0f);                 x += sz + spacing;  // Square with all rounded corners

imgui_draw.cpp

@@ -1104,6 +1104,30 @@ void ImDrawList::AddCircleFilled(const ImVec2& center, float radius, ImU32 col,
     PathFillConvex(col);
 }
 
+// Guaranteed to honor 'num_segments'
+void ImDrawList::AddNgon(const ImVec2& center, float radius, ImU32 col, int num_segments, float thickness)
+{
+    if ((col & IM_COL32_A_MASK) == 0 || num_segments <= 2)
+        return;
+
+    // Because we are filling a closed shape we remove 1 from the count of segments/points
+    const float a_max = (IM_PI * 2.0f) * ((float)num_segments - 1.0f) / (float)num_segments;
+    PathArcTo(center, radius - 0.5f, 0.0f, a_max, num_segments - 1);
+    PathStroke(col, true, thickness);
+}
+
+// Guaranteed to honor 'num_segments'
+void ImDrawList::AddNgonFilled(const ImVec2& center, float radius, ImU32 col, int num_segments)
+{
+    if ((col & IM_COL32_A_MASK) == 0 || num_segments <= 2)
+        return;
+
+    // Because we are filling a closed shape we remove 1 from the count of segments/points
+    const float a_max = (IM_PI * 2.0f) * ((float)num_segments - 1.0f) / (float)num_segments;
+    PathArcTo(center, radius, 0.0f, a_max, num_segments - 1);
+    PathFillConvex(col);
+}
+
 void ImDrawList::AddBezierCurve(const ImVec2& pos0, const ImVec2& cp0, const ImVec2& cp1, const ImVec2& pos1, ImU32 col, float thickness, int num_segments)
 {
     if ((col & IM_COL32_A_MASK) == 0)