ImDrawList: Fixed AddCircle(), AddCircleFilled() angle step being off, which was visible when drawing a "circle" with a small number of segments (e.g. an hexagon). (#2287) [@baktery]

+ Demo tweaks

docs/CHANGELOG.txt

@@ -34,6 +34,8 @@ HOW TO UPDATE?
 -----------------------------------------------------------------------
 
 Other Changes:
+- ImDrawList: Fixed AddCircle(), AddCircleFilled() angle step being off, which was visible when drawing a "circle"
+  with a small number of segments (e.g. an hexagon). (#2287) [@baktery]
 - Fonts: imgui_freetype: Added support for imgui allocators + custom FreeType only SetAllocatorFunctions. (#2285) [@Vuhdo]
 - Examples: Win32: Using GetForegroundWindow() instead of GetActiveWindow() to be compatible with windows created 
   in a different thread. (#1951, #2087, #2156, #2232) [many people]

docs/TODO.txt

@@ -38,7 +38,7 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - drawlist: maintaining bounding box per command would allow to merge draw command when clipping isn't relied on (typical non-scrolling window or non-overflowing column would merge with previous command).
  - drawlist: primitives/helpers to manipulate vertices post submission, so e.g. a quad/rect can be resized to fit later submitted content, _without_ using the ChannelSplit api
  - drawlist: make it easier to toggle AA per primitive, so we can use e.g. non-AA fill + AA borders more naturally
- - drawlist: non-AA strokes have gaps between points (#593, #288), especially RenderCheckmark().
+ - drawlist: non-AA strokes have gaps between points (#593, #288), glitch especially on RenderCheckmark() and ColorPicker4().
  - drawlist: would be good to be able to deep copy of ImDrawData (we have a deep copy of ImDrawList now).
  - drawlist: rendering: provide a way for imgui to output to a single/global vertex buffer, re-order indices only at the end of the frame (ref: https://gist.github.com/floooh/10388a0afbe08fce9e617d8aefa7d302)
  - drawlist: callback: add an extra void* in ImDrawCallback to allow passing render-local data to the callback (would break API).

imgui_demo.cpp

@@ -3852,27 +3852,30 @@ static void ShowExampleAppCustomRendering(bool* p_open)
     static ImVec4 col = 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::ColorEdit3("Color", &col.x);
+    ImGui::ColorEdit4("Color", &col.x);
     {
         const ImVec2 p = ImGui::GetCursorScreenPos();
         const ImU32 col32 = ImColor(col);
         float x = p.x + 4.0f, y = p.y + 4.0f, spacing = 8.0f;
         for (int n = 0; n < 2; n++)
         {
-            float curr_thickness = (n == 0) ? 1.0f : thickness;
+            // First line uses a thickness of 1.0, second line uses the configurable thickness
-            draw_list->AddCircle(ImVec2(x+sz*0.5f, y+sz*0.5f), sz*0.5f, col32, 20, curr_thickness); x += sz+spacing;
+            float th = (n == 0) ? 1.0f : thickness;
-            draw_list->AddRect(ImVec2(x, y), ImVec2(x+sz, y+sz), col32, 0.0f, ImDrawCornerFlags_All, curr_thickness); x += sz+spacing;
+            draw_list->AddCircle(ImVec2(x+sz*0.5f, y+sz*0.5f), sz*0.5f, col32, 6, th); x += sz+spacing;     // Hexagon
-            draw_list->AddRect(ImVec2(x, y), ImVec2(x+sz, y+sz), col32, 10.0f, ImDrawCornerFlags_All, curr_thickness); x += sz+spacing;
+            draw_list->AddCircle(ImVec2(x+sz*0.5f, y+sz*0.5f), sz*0.5f, col32, 20, th); x += sz+spacing;    // Circle
-            draw_list->AddRect(ImVec2(x, y), ImVec2(x+sz, y+sz), col32, 10.0f, ImDrawCornerFlags_TopLeft|ImDrawCornerFlags_BotRight, curr_thickness); x += sz+spacing;
+            draw_list->AddRect(ImVec2(x, y), ImVec2(x+sz, y+sz), col32, 0.0f, ImDrawCornerFlags_All, th); x += sz+spacing;
-            draw_list->AddTriangle(ImVec2(x+sz*0.5f, y), ImVec2(x+sz,y+sz-0.5f), ImVec2(x,y+sz-0.5f), col32, curr_thickness); x += sz+spacing;
+            draw_list->AddRect(ImVec2(x, y), ImVec2(x+sz, y+sz), col32, 10.0f, ImDrawCornerFlags_All, th); x += sz+spacing;
-            draw_list->AddLine(ImVec2(x, y), ImVec2(x+sz, y   ), col32, curr_thickness); x += sz+spacing;   // Horizontal line (note: drawing a filled rectangle will be faster!)
+            draw_list->AddRect(ImVec2(x, y), ImVec2(x+sz, y+sz), col32, 10.0f, ImDrawCornerFlags_TopLeft|ImDrawCornerFlags_BotRight, th); x += sz+spacing;
-            draw_list->AddLine(ImVec2(x, y), ImVec2(x,    y+sz), col32, curr_thickness); x += spacing;      // Vertical line (note: drawing a filled rectangle will be faster!)
+            draw_list->AddTriangle(ImVec2(x+sz*0.5f, y), ImVec2(x+sz,y+sz-0.5f), ImVec2(x,y+sz-0.5f), col32, th); x += sz+spacing;
-            draw_list->AddLine(ImVec2(x, y), ImVec2(x+sz, y+sz), col32, curr_thickness); x += sz+spacing;   // Diagonal line
+            draw_list->AddLine(ImVec2(x, y), ImVec2(x+sz, y   ), col32, th); x += sz+spacing;               // Horizontal line (note: drawing a filled rectangle will be faster!)
-            draw_list->AddBezierCurve(ImVec2(x, y), ImVec2(x+sz*1.3f,y+sz*0.3f), ImVec2(x+sz-sz*1.3f,y+sz-sz*0.3f), ImVec2(x+sz, y+sz), col32, curr_thickness);
+            draw_list->AddLine(ImVec2(x, y), ImVec2(x,    y+sz), col32, th); x += spacing;                  // Vertical line (note: drawing a filled rectangle will be faster!)
+            draw_list->AddLine(ImVec2(x, y), ImVec2(x+sz, y+sz), col32, th); x += sz+spacing;               // Diagonal line
+            draw_list->AddBezierCurve(ImVec2(x, y), ImVec2(x+sz*1.3f,y+sz*0.3f), ImVec2(x+sz-sz*1.3f,y+sz-sz*0.3f), ImVec2(x+sz, y+sz), col32, th);
             x = p.x + 4;
             y += sz+spacing;
         }
-        draw_list->AddCircleFilled(ImVec2(x+sz*0.5f, y+sz*0.5f), sz*0.5f, col32, 32); x += sz+spacing;
+        draw_list->AddCircleFilled(ImVec2(x+sz*0.5f, y+sz*0.5f), sz*0.5f, col32, 6); x += sz+spacing;       // Hexagon
+        draw_list->AddCircleFilled(ImVec2(x+sz*0.5f, y+sz*0.5f), sz*0.5f, col32, 32); x += sz+spacing;      // Circle
         draw_list->AddRectFilled(ImVec2(x, y), ImVec2(x+sz, y+sz), col32); x += sz+spacing;
         draw_list->AddRectFilled(ImVec2(x, y), ImVec2(x+sz, y+sz), col32, 10.0f); x += sz+spacing;
         draw_list->AddRectFilled(ImVec2(x, y), ImVec2(x+sz, y+sz), col32, 10.0f, ImDrawCornerFlags_TopLeft|ImDrawCornerFlags_BotRight); x += sz+spacing;

imgui_draw.cpp

@@ -955,6 +955,9 @@ void ImDrawList::PathArcTo(const ImVec2& centre, float radius, float a_min, floa
         _Path.push_back(centre);
         return;
     }
+
+    // Note that we are adding a point at both a_min and a_max. 
+    // If you are trying to draw a full closed circle you don't want the overlapping points!
     _Path.reserve(_Path.Size + (num_segments + 1));
     for (int i = 0; i <= num_segments; i++)
     {
@@ -1138,21 +1141,23 @@ void ImDrawList::AddTriangleFilled(const ImVec2& a, const ImVec2& b, const ImVec
 
 void ImDrawList::AddCircle(const ImVec2& centre, float radius, ImU32 col, int num_segments, float thickness)
 {
-    if ((col & IM_COL32_A_MASK) == 0)
+    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(centre, radius-0.5f, 0.0f, a_max, num_segments);
+    PathArcTo(centre, radius-0.5f, 0.0f, a_max, num_segments - 1);
     PathStroke(col, true, thickness);
 }
 
 void ImDrawList::AddCircleFilled(const ImVec2& centre, float radius, ImU32 col, int num_segments)
 {
-    if ((col & IM_COL32_A_MASK) == 0)
+    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(centre, radius, 0.0f, a_max, num_segments);
+    PathArcTo(centre, radius, 0.0f, a_max, num_segments - 1);
     PathFillConvex(col);
 }