ImDrawList: Internals: Added IM_DRAWLIST_ARCFAST_TESSELLATION_MULTIPLIER setting.

imgui_draw.cpp

@@ -355,10 +355,10 @@ ImDrawListSharedData::ImDrawListSharedData()
     InitialFlags = ImDrawListFlags_None;
 
     // Lookup tables
-    for (int i = 0; i < IM_ARRAYSIZE(CircleVtx12); i++)
+    for (int i = 0; i < IM_ARRAYSIZE(ArcFastVtx); i++)
     {
-        const float a = ((float)i * 2 * IM_PI) / (float)IM_ARRAYSIZE(CircleVtx12);
-        CircleVtx12[i] = ImVec2(ImCos(a), ImSin(a));
+        const float a = ((float)i * 2 * IM_PI) / (float)IM_ARRAYSIZE(ArcFastVtx);
+        ArcFastVtx[i] = ImVec2(ImCos(a), ImSin(a));
     }
     memset(CircleSegmentCounts, 0, sizeof(CircleSegmentCounts)); // This will be set by SetCircleSegmentMaxError()
 }
@@ -898,10 +898,18 @@ void ImDrawList::PathArcToFast(const ImVec2& center, float radius, int a_min_of_
         _Path.push_back(center);
         return;
     }
+
+    // For legacy reason the PathArcToFast() always takes angles where 2*PI is represented by 12,
+    // but it is possible to set IM_DRAWLIST_ARCFAST_TESSELATION_MULTIPLIER to a higher value. This should compile to a no-op otherwise.
+#if IM_DRAWLIST_ARCFAST_TESSELLATION_MULTIPLIER != 1
+    a_min_of_12 *= IM_DRAWLIST_ARCFAST_TESSELLATION_MULTIPLIER;
+    a_max_of_12 *= IM_DRAWLIST_ARCFAST_TESSELLATION_MULTIPLIER;
+#endif
+
     _Path.reserve(_Path.Size + (a_max_of_12 - a_min_of_12 + 1));
     for (int a = a_min_of_12; a <= a_max_of_12; a++)
     {
-        const ImVec2& c = _Data->CircleVtx12[a % IM_ARRAYSIZE(_Data->CircleVtx12)];
+        const ImVec2& c = _Data->ArcFastVtx[a % IM_ARRAYSIZE(_Data->ArcFastVtx)];
         _Path.push_back(ImVec2(center.x + c.x * radius, center.y + c.y * radius));
     }
 }

imgui_internal.h

@@ -863,11 +863,16 @@ struct ImGuiColumns
     }
 };
 
-// Helper function to calculate a circle's segment count given its radius and a "maximum error" value.
+// ImDrawList: Helper function to calculate a circle's segment count given its radius and a "maximum error" value.
 #define IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MIN                     12
 #define IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MAX                     512
 #define IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_CALC(_RAD,_MAXERROR)    ImClamp((int)((IM_PI * 2.0f) / ImAcos(((_RAD) - (_MAXERROR)) / (_RAD))), IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MIN, IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MAX)
 
+// ImDrawList: You may set this to higher values (e.g. 2 or 3) to increase tessellation of fast rounded corners path.
+#ifndef IM_DRAWLIST_ARCFAST_TESSELLATION_MULTIPLIER
+#define IM_DRAWLIST_ARCFAST_TESSELLATION_MULTIPLIER             1
+#endif
+
 // Data shared between all ImDrawList instances
 // You may want to create your own instance of this if you want to use ImDrawList completely without ImGui. In that case, watch out for future changes to this structure.
 struct IMGUI_API ImDrawListSharedData
@@ -881,7 +886,7 @@ struct IMGUI_API ImDrawListSharedData
     ImDrawListFlags InitialFlags;               // Initial flags at the beginning of the frame (it is possible to alter flags on a per-drawlist basis afterwards)
 
     // [Internal] Lookup tables
-    ImVec2          CircleVtx12[12];            // FIXME: Bake rounded corners fill/borders in atlas
+    ImVec2          ArcFastVtx[12 * IM_DRAWLIST_ARCFAST_TESSELLATION_MULTIPLIER];  // FIXME: Bake rounded corners fill/borders in atlas
     ImU8            CircleSegmentCounts[64];    // Precomputed segment count for given radius (array index + 1) before we calculate it dynamically (to avoid calculation overhead)
 
     ImDrawListSharedData();