ImDrawList: Fix AddCircle{Filled} with 12 segment case (#4419, #4421)

docs/CHANGELOG.txt

@@ -92,7 +92,9 @@ Other Changes:
 - Fonts: Prefer using U+FFFD character for fallback instead of '?', if available. (#4269)
 - Fonts: Use U+FF0E dot character to construct an ellipsis if U+002E '.' is not available. (#4269)
 - Fonts: Add U+FFFD ("replacement character") to default asian glyphs ranges. (#4269)
-- Fonts: Fix calling ClearTexData() (clearing CPU side font data) triggering an assert in NewFrame(). (#3487)
+- Fonts: Fixed calling ClearTexData() (clearing CPU side font data) triggering an assert in NewFrame(). (#3487)
+- DrawList: Fixed AddCircle/AddCircleFilled() with auto-tesselation not using accelerated paths for small circles.
+  Fixed AddCircle/AddCircleFilled() with 12 segments which had a broken edge. (#4419, #4421) [@thedmd]
 - Demo: Fixed requirement in 1.83 to link with imgui_demo.cpp if IMGUI_DISABLE_METRICS_WINDOW is not set. (#4171)
   Normally the right way to disable compiling the demo is to set IMGUI_DISABLE_DEMO_WINDOWS, but we want to avoid
   implying that the file is required.

imgui_draw.cpp

@@ -1479,24 +1479,22 @@ void ImDrawList::AddCircle(const ImVec2& center, float radius, ImU32 col, int nu
     if ((col & IM_COL32_A_MASK) == 0 || radius <= 0.0f)
         return;
 
-    // Obtain segment count
     if (num_segments <= 0)
     {
-        // Automatic segment count
-        num_segments = _CalcCircleAutoSegmentCount(radius);
+        // Use arc with automatic segment count
+        _PathArcToFastEx(center, radius - 0.5f, 0, IM_DRAWLIST_ARCFAST_SAMPLE_MAX, 0);
+        _Path.Size--;
     }
     else
     {
         // Explicit segment count (still clamp to avoid drawing insanely tessellated shapes)
         num_segments = ImClamp(num_segments, 3, IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MAX);
-    }
 
-    // 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;
-    if (num_segments == 12)
-        PathArcToFast(center, radius - 0.5f, 0, 12 - 1);
-    else
+        // 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, ImDrawFlags_Closed, thickness);
 }
 
@@ -1505,24 +1503,22 @@ void ImDrawList::AddCircleFilled(const ImVec2& center, float radius, ImU32 col,
     if ((col & IM_COL32_A_MASK) == 0 || radius <= 0.0f)
         return;
 
-    // Obtain segment count
     if (num_segments <= 0)
     {
-        // Automatic segment count
-        num_segments = _CalcCircleAutoSegmentCount(radius);
+        // Use arc with automatic segment count
+        _PathArcToFastEx(center, radius, 0, IM_DRAWLIST_ARCFAST_SAMPLE_MAX, 0);
+        _Path.Size--;
     }
     else
     {
         // Explicit segment count (still clamp to avoid drawing insanely tessellated shapes)
         num_segments = ImClamp(num_segments, 3, IM_DRAWLIST_CIRCLE_AUTO_SEGMENT_MAX);
-    }
 
-    // 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;
-    if (num_segments == 12)
-        PathArcToFast(center, radius, 0, 12 - 1);
-    else
+        // 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);
 }