Add rounded rectangle support (fix #2184)

data/extensions/aseprite-theme/dark/theme.xml

@@ -393,6 +393,7 @@
         <part id="icon_slice" x="248" y="264" w="8" h="8"/>
         <part id="icon_aspect_ratio" x="256" y="264" w="10" h="8"/>
         <part id="icon_delta" x="266" y="264" w="6" h="8"/>
+        <part id="icon_corner_radius" x="272" y="264" w="8" h="8"/>
         <part id="icon_add" x="184" y="200" w="5" h="5"/>
         <part id="tool_rectangular_marquee" x="144" y="0" w="16" h="16"/>
         <part id="tool_elliptical_marquee" x="160" y="0" w="16" h="16"/>

data/extensions/aseprite-theme/theme.xml

@@ -389,6 +389,7 @@
         <part id="icon_slice" x="248" y="264" w="8" h="8"/>
         <part id="icon_aspect_ratio" x="256" y="264" w="10" h="8"/>
         <part id="icon_delta" x="266" y="264" w="6" h="8"/>
+        <part id="icon_corner_radius" x="272" y="264" w="8" h="8"/>
         <part id="icon_add" x="184" y="200" w="5" h="5"/>
         <part id="tool_rectangular_marquee" x="144" y="0" w="16" h="16"/>
         <part id="tool_elliptical_marquee" x="160" y="0" w="16" h="16"/>

data/gui.xml

@@ -678,6 +678,8 @@
       <!-- Modifiers for two-points tool controller -->
       <key action="SquareAspect" shortcut="Shift" />
       <key action="DrawFromCenter" shortcut="Ctrl" />
+      <key action="CornerRadius" shortcut="J" />
+
       <!-- Modifiers for two-or-more-points tools -->
       <key action="MoveOrigin" shortcut="Space" />
       <key action="RotateShape" shortcut="Alt" />

data/strings/en.ini

@@ -1006,6 +1006,7 @@ move_origin = Move Origin
 square_aspect = Square Aspect
 draw_from_center = Draw From Center
 rotate_shape = Rotate Shape
+corner_radius = Corner Radius
 trigger_left_mouse_button = Trigger Left Mouse Button
 trigger_right_mouse_button = Trigger Right Mouse Button
 ok = &OK

src/app/tools/controller.h

@@ -62,6 +62,10 @@ public:
   // Returns the angle for a shape-like intertwiner (rectangles,
   // ellipses, etc.).
   virtual double getShapeAngle() const { return 0.0; }
+
+  // Returns the radius for each corner for a rectangle intertwiner when drawing
+  // rounded rectangles.
+  virtual int getCornerRadius() const { return 0; }
 };
 
 }} // namespace app::tools

src/app/tools/controllers.h

@@ -1,11 +1,15 @@
 // Aseprite
-// Copyright (C) 2019-2023  Igara Studio S.A.
+// Copyright (C) 2019-2025  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
 // the End-User License Agreement for Aseprite.
 
 #include "app/snap_to_grid.h"
+#include "app/tools/controller.h"
+#include "app/tools/intertwine.h"
+#include "app/tools/tool_loop.h"
+#include "app/tools/tool_loop_modifiers.h"
 #include "base/gcd.h"
 #include "base/pi.h"
 #include "fmt/format.h"
@@ -135,6 +139,12 @@ public:
     if (MoveOriginCapability::isMovingOrigin(loop, stroke, pt))
       return;
 
+    if ((int(loop->getModifiers()) & int(ToolLoopModifiers::kCornerRadius))) {
+      int dr = stroke[1].y - pt.y;
+      m_cornerRadius = ABS(m_lastCornerRadius + dr);
+      return;
+    }
+
     if (!loop->getIntertwine()->snapByAngle() &&
         int(loop->getModifiers()) & int(ToolLoopModifiers::kRotateShape)) {
       if ((int(loop->getModifiers()) & int(ToolLoopModifiers::kFromCenter))) {
@@ -149,8 +159,13 @@ public:
       return;
     }
 
-    stroke[0] = m_first;
-    stroke[1] = pt;
+    if (m_lastCornerRadius != m_cornerRadius) {
+      m_lastCornerRadius = m_cornerRadius;
+    }
+    else {
+      stroke[0] = m_first;
+      stroke[1] = pt;
+    }
 
     bool isoAngle = false;
 
@@ -277,11 +292,16 @@ public:
       text += fmt::format(" :angle: {:.1f}", 180.0 * angle / PI);
     }
 
+    if (hasCornerRadius()) {
+      text += fmt::format(" :corner_radius: {}", m_cornerRadius);
+    }
+
     // Aspect ratio at the end
     text += fmt::format(" :aspect_ratio: {}:{}", w / gcd, h / gcd);
   }
 
   double getShapeAngle() const override { return m_angle; }
+  int getCornerRadius() const override { return m_cornerRadius; }
 
 private:
   void snapPointsToGridTiles(ToolLoop* loop, Stroke& stroke)
@@ -301,6 +321,8 @@ private:
 
   bool hasAngle() const { return (ABS(m_angle) > 0.001); }
 
+  bool hasCornerRadius() const { return (ABS(m_cornerRadius) > 1); }
+
   void onMoveOrigin(const Point& delta) override
   {
     m_first.x += delta.x;
@@ -312,6 +334,8 @@ private:
   Stroke::Pt m_first;
   Stroke::Pt m_center;
   double m_angle;
+  int m_lastCornerRadius = 0;
+  int m_cornerRadius = 0;
 };
 
 // Controls clicks for tools like polygon

src/app/tools/intertwine.cpp

@@ -18,6 +18,7 @@
 #include "app/tools/tool_loop.h"
 #include "base/pi.h"
 #include "doc/algo.h"
+#include "doc/algorithm/hline.h"
 #include "doc/layer.h"
 
 #include <cmath>
@@ -158,4 +159,21 @@ doc::AlgoLineWithAlgoPixel Intertwine::getLineAlgo(ToolLoop* loop,
   }
 }
 
+// static
+void Intertwine::doPointshapeCircle(int xm, int ym, int r, int sx, int sy, ToolLoop* loop, bool fill)
+{
+  if (fill) {
+    algo_circlefill(xm, ym, sx, sy, r, loop, (AlgoHLine)doPointshapeHline);
+  }
+  else {
+    algo_circle(xm, ym, sx, sy, r, loop, (AlgoPixel)doPointshapePoint);
+  }
+}
+
+// static
+void Intertwine::doPointshapeArc(int xm, int ym, double sa, double ea, int r, ToolLoop* loop)
+{
+  algo_arc(xm, ym, sa, ea, r, loop, (AlgoPixel)doPointshapePoint);
+}
+
 }} // namespace app::tools

src/app/tools/intertwine.h

@@ -60,6 +60,11 @@ protected:
   static doc::AlgoLineWithAlgoPixel getLineAlgo(ToolLoop* loop,
                                                 const Stroke::Pt& a,
                                                 const Stroke::Pt& b);
+
+  static void
+  doPointshapeCircle(int xm, int ym, int r, int sx, int sy, ToolLoop* loop, bool fill = false);
+
+  static void doPointshapeArc(int xm, int ym, double sa, double ea, int r, ToolLoop* loop);
 };
 
 }} // namespace app::tools

src/app/tools/intertwiners.h

@@ -5,8 +5,18 @@
 // This program is distributed under the terms of
 // the End-User License Agreement for Aseprite.
 
+#include "app/tools/controller.h"
+#include "app/tools/intertwine.h"
+#include "app/tools/point_shape.h"
+#include "app/tools/tool_loop.h"
+#include "app/tools/tool_loop_modifiers.h"
 #include "base/pi.h"
+#include "doc/algorithm/polygon.h"
 #include "doc/layer_tilemap.h"
+#include "gfx/point.h"
+#include <algorithm>
+
+using namespace gfx;
 
 namespace app { namespace tools {
 
@@ -183,22 +193,52 @@ public:
           std::swap(y1, y2);
 
         const double angle = loop->getController()->getShapeAngle();
+        const int cornerRadius = loop->getController()->getCornerRadius();
         if (ABS(angle) < 0.001) {
-          doPointshapeLineWithoutDynamics(x1, y1, x2, y1, loop);
-          doPointshapeLineWithoutDynamics(x1, y2, x2, y2, loop);
+          int r = 0;
+          if (cornerRadius > 1) {
+            int w = x2 - x1;
+            int h = y2 - y1;
+            int xm = x1 + w / 2;
+            int ym = y1 + h / 2;
+            r = std::min(w, std::min(h, 2 * cornerRadius)) / 2;
+            doPointshapeCircle(xm, ym, r, w - r * 2, h - r * 2, loop);
+          }
 
-          for (y = y1; y <= y2; y++) {
+          doPointshapeLineWithoutDynamics(x1 + r, y1, x2 - r, y1, loop);
+          doPointshapeLineWithoutDynamics(x1 + r, y2, x2 - r, y2, loop);
+
+          for (y = y1 + r; y <= y2 - r; y++) {
             doPointshapePoint(x1, y, loop);
             doPointshapePoint(x2, y, loop);
           }
         }
         else {
-          Stroke p = rotateRectangle(x1, y1, x2, y2, angle);
-          int n = p.size();
-          for (int i = 0; i + 1 < n; ++i) {
-            doPointshapeLine(p[i], p[i + 1], loop);
+          if (cornerRadius <= 1) {
+            Stroke p = rotateRectangle(x1, y1, x2, y2, angle);
+            int n = p.size();
+            for (int i = 0; i + 1 < n; ++i) {
+              doPointshapeLine(p[i], p[i + 1], loop);
+            }
+            doPointshapeLine(p[n - 1], p[0], loop);
+          }
+          else {
+            int w = x2 - x1;
+            int h = y2 - y1;
+            int r = std::min(w, std::min(h, 2 * cornerRadius)) / 2;
+            Stroke p = rotateRectangle(x1, y1, x2, y2, angle, r);
+            int n = p.size();
+            for (int i = 0; i + 1 < n; i += 3) {
+              doPointshapeLine(p[i], p[i + 1], loop);
+            }
+            const double ang_minus_PI_2 = base::fmod_radians(angle - PI / 2);
+            const double ang_plus_PI_2 = base::fmod_radians(angle + PI / 2);
+            const double ang_plus_PI = base::fmod_radians(angle + PI);
+            doPointshapeArc(p[2].x, p[2].y, ang_minus_PI_2, angle, r, loop);
+            doPointshapeArc(p[5].x, p[5].y, angle, ang_plus_PI_2, r, loop);
+            doPointshapeArc(p[8].x, p[8].y, ang_plus_PI_2, ang_plus_PI, r, loop);
+            doPointshapeArc(p[11].x, p[11].y, ang_plus_PI, ang_minus_PI_2, r, loop);
           }
-          doPointshapeLine(p[n - 1], p[0], loop);
         }
       }
     }
@@ -224,14 +264,44 @@ public:
         std::swap(y1, y2);
 
       const double angle = loop->getController()->getShapeAngle();
+      const int cornerRadius = loop->getController()->getCornerRadius();
       if (ABS(angle) < 0.001) {
-        for (y = y1; y <= y2; y++)
+        int r = 0;
+        if (cornerRadius > 1) {
+          int w = x2 - x1;
+          int h = y2 - y1;
+          int xm = x1 + w / 2;
+          int ym = y1 + h / 2;
+          r = std::min(w, std::min(h, 2 * cornerRadius)) / 2;
+          doPointshapeCircle(xm, ym, r, w - r * 2, h - r * 2, loop, true);
+
+          for (y = y1; y < y1 + r; y++)
+            doPointshapeLineWithoutDynamics(x1 + r, y, x2 - r, y, loop);
+          for (y = y2 - r + 1; y <= y2; y++)
+            doPointshapeLineWithoutDynamics(x1 + r, y, x2 - r, y, loop);
+        }
+
+        for (y = y1 + r; y <= y2 - r; y++)
           doPointshapeLineWithoutDynamics(x1, y, x2, y, loop);
       }
       else {
-        Stroke p = rotateRectangle(x1, y1, x2, y2, angle);
-        auto v = p.toXYInts();
-        doc::algorithm::polygon(v.size() / 2, &v[0], loop, (AlgoHLine)doPointshapeHline);
+        if (cornerRadius <= 1) {
+          Stroke p = rotateRectangle(x1, y1, x2, y2, angle);
+          auto v = p.toXYInts();
+          doc::algorithm::polygon(v.size() / 2, &v[0], loop, (AlgoHLine)doPointshapeHline);
+        }
+        else {
+          int w = x2 - x1;
+          int h = y2 - y1;
+          int r = std::min(w, std::min(h, 2 * cornerRadius)) / 2;
+          Stroke p = rotateRectangle(x1, y1, x2, y2, angle, cornerRadius);
+          auto v = p.toXYInts();
+          doc::algorithm::polygon(v.size() / 2, &v[0], loop, (AlgoHLine)doPointshapeHline);
+          doPointshapeCircle(p[2].x, p[2].y, r, 0, 0, loop, true);
+          doPointshapeCircle(p[5].x, p[5].y, r, 0, 0, loop, true);
+          doPointshapeCircle(p[8].x, p[8].y, r, 0, 0, loop, true);
+          doPointshapeCircle(p[11].x, p[11].y, r, 0, 0, loop, true);
+        }
       }
     }
   }
@@ -274,6 +344,54 @@ private:
     stroke.addPoint(Point(cx - a * c + b * s, cy + a * s + b * c));
     return stroke;
   }
+
+  // Returns a stroke with the rotated points of a rectangle making room for a
+  // rounded corner of the specified radius, and with points where the center of
+  // each corner must be.
+  static Stroke rotateRectangle(int x1, int y1, int x2, int y2, double angle, int cornerRadius)
+  {
+    cornerRadius = std::max(cornerRadius, 0);
+
+    int cx = (x1 + x2) / 2;
+    int cy = (y1 + y2) / 2;
+    int a = ((x2 - x1) / 2);
+    int b = ((y2 - y1) / 2);
+    int ai = a - cornerRadius;
+    int bi = b - cornerRadius;
+
+    double s = -std::sin(angle);
+    double c = std::cos(angle);
+
+    Stroke stroke;
+    // Top segment
+    stroke.addPoint(Point(cx - ai * c - b * s, cy + ai * s - b * c));
+    stroke.addPoint(Point(cx + ai * c - b * s, cy - ai * s - b * c));
+
+    // Center for top-right corner
+    stroke.addPoint(Point(cx + ai * c - bi * s, cy - ai * s - bi * c));
+
+    // Right segment
+    stroke.addPoint(Point(cx + a * c - bi * s, cy - a * s - bi * c));
+    stroke.addPoint(Point(cx + a * c + bi * s, cy - a * s + bi * c));
+
+    // Center for bottom-right corner
+    stroke.addPoint(Point(cx + ai * c + bi * s, cy - ai * s + bi * c));
+
+    // Bottom segment
+    stroke.addPoint(Point(cx + ai * c + b * s, cy - ai * s + b * c));
+    stroke.addPoint(Point(cx - ai * c + b * s, cy + ai * s + b * c));
+
+    // Center for bottom-left corner
+    stroke.addPoint(Point(cx - ai * c + bi * s, cy + ai * s + bi * c));
+
+    // Left segment
+    stroke.addPoint(Point(cx - a * c + bi * s, cy + a * s + bi * c));
+    stroke.addPoint(Point(cx - a * c - bi * s, cy + a * s - bi * c));
+
+    // Center for top-left corner
+    stroke.addPoint(Point(cx - ai * c - bi * s, cy + ai * s - bi * c));
+    return stroke;
+  }
 };
 
 class IntertwineAsEllipses : public Intertwine {

src/app/tools/tool_loop_modifiers.h

@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018  Igara Studio S.A.
+// Copyright (C) 2018-2025  Igara Studio S.A.
 // Copyright (C) 2016-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -21,6 +21,7 @@ enum class ToolLoopModifiers {
   kSquareAspect = 0x00000020,
   kFromCenter = 0x00000040,
   kRotateShape = 0x00000080,
+  kCornerRadius = 0x00000100,
 };
 
 }} // namespace app::tools

src/app/ui/editor/editor.cpp

@@ -1834,7 +1834,7 @@ void Editor::updateToolLoopModifiersIndicators(const bool firstFromMouseDown)
         // square-aspect/rotation/etc. only when the user presses the
         // modifier key again in the ToolLoop (and not before starting
         // the loop). So Alt+selection will add a selection, but
-        // willn't start the square-aspect until we press Alt key
+        // won't start the square-aspect until we press Alt key
         // again, or Alt+Shift+selection tool will subtract the
         // selection but will not start the rotation until we release
         // and press the Alt key again.
@@ -1847,6 +1847,8 @@ void Editor::updateToolLoopModifiersIndicators(const bool firstFromMouseDown)
             modifiers |= int(tools::ToolLoopModifiers::kFromCenter);
           if (int(action & KeyAction::RotateShape))
             modifiers |= int(tools::ToolLoopModifiers::kRotateShape);
+          if (int(action & KeyAction::CornerRadius))
+            modifiers |= int(tools::ToolLoopModifiers::kCornerRadius);
         }
       }
 

src/app/ui/key.cpp

@@ -110,6 +110,10 @@ const std::vector<KeyShortcutAction>& actions()
        I18N_KEY(rotate_shape),
        app::KeyAction::RotateShape,
        app::KeyContext::ShapeTool            },
+      { "CornerRadius",
+       I18N_KEY(corner_radius),
+       app::KeyAction::CornerRadius,
+       app::KeyContext::ShapeTool            },
       { "LeftMouseButton",
        I18N_KEY(trigger_left_mouse_button),
        app::KeyAction::LeftMouseButton,
@@ -392,6 +396,7 @@ Key::Key(const KeyAction action, const KeyContext keyContext)
     case KeyAction::RotateShape:               m_keycontext = KeyContext::ShapeTool; break;
     case KeyAction::LeftMouseButton:
     case KeyAction::RightMouseButton:          m_keycontext = KeyContext::Any; break;
+    case KeyAction::CornerRadius:              m_keycontext = KeyContext::ShapeTool; break;
   }
 }
 

src/app/ui/key.h

@@ -64,6 +64,7 @@ enum class KeyAction {
   AngleSnapFromLastPoint = 0x00010000,
   RotateShape = 0x00020000,
   FineControl = 0x00040000,
+  CornerRadius = 0x00080000,
 };
 
 enum class WheelAction {

src/doc/algo.cpp

@@ -12,6 +12,7 @@
 #include "doc/algo.h"
 
 #include "base/debug.h"
+#include "base/pi.h"
 
 #include <algorithm>
 #include <cmath>
@@ -180,6 +181,183 @@ void algo_line_continuous_with_fix_for_line_brush(int x0,
   }
 }
 
+// Circle code based on Alois Zingl work released under the MIT
+// license http://members.chello.at/easyfilter/bresenham.html
+//
+// Adapted for Aseprite by Igara Studio S.A.
+//
+// Draws a circle divided in 4 parts, separated sx pixels horizontally and sy
+// pixels vertically:
+//             |---sx---|
+//
+//          OOO          OOO
+//        O                  O
+//       O                    O
+//  T
+//  |
+//  |
+//  sy           xm,xy
+//  |
+//  |
+//  _
+//       O                    O
+//        O                  O
+//          OOO          OOO
+//
+// If sx and sy are 0, it draws a regular circle.
+void algo_circle(int xm, int ym, int sx, int sy, int r, void* data, AlgoPixel proc)
+{
+  int x = -r, y = 0, err = 2 - 2 * r; /* II. Quadrant */
+  sx = sx < 0 ? 0 : sx;
+  sy = sy < 0 ? 0 : sy;
+  int offsetx = sx / 2;
+  int offsety = sy / 2;
+  // Fix the position when sx or sy are not even.
+  int fixx = sx - 2 * offsetx;
+  int fixy = sy - 2 * offsety;
+  do {
+    proc(xm - x + offsetx + fixx, ym + y + offsety + fixy, data); /*   I. Quadrant */
+    proc(xm - y - offsetx, ym - x + offsety + fixy, data);        /*  II. Quadrant */
+    proc(xm + x - offsetx, ym - y - offsety, data);               /* III. Quadrant */
+    proc(xm + y + offsetx + fixx, ym + x - offsety, data);        /*  IV. Quadrant */
+    r = err;
+    if (r <= y)
+      err += ++y * 2 + 1; /* e_xy+e_y < 0 */
+    if (r > x || err > y)
+      err += ++x * 2 + 1; /* e_xy+e_x > 0 or no 2nd y-step */
+  } while (x < 0);
+}
+
+// Same as algo_circle but with the parts filled.
+void algo_circlefill(int xm, int ym, int sx, int sy, int r, void* data, AlgoHLine proc)
+{
+  int x = -r, y = 0, err = 2 - 2 * r; /* II. Quadrant */
+  sx = sx < 0 ? 0 : sx;
+  sy = sy < 0 ? 0 : sy;
+  int offsetx = sx / 2;
+  int offsety = sy / 2;
+  // Fix the position when sx or sy are not even.
+  int fixx = sx - 2 * offsetx;
+  int fixy = sy - 2 * offsety;
+  do {
+    proc(xm, ym + y + offsety + fixy, xm - x + offsetx + fixx, data); /*   I. Quadrant */
+    proc(xm - y - offsetx, ym - x + offsety + fixy, xm, data);        /*  II. Quadrant */
+    proc(xm + x - offsetx, ym - y - offsety, xm, data);               /* III. Quadrant */
+    proc(xm, ym + x - offsety, xm + y + offsetx + fixx, data);        /*  IV. Quadrant */
+    r = err;
+    if (r <= y)
+      err += ++y * 2 + 1; /* e_xy+e_y < 0 */
+    if (r > x || err > y)
+      err += ++x * 2 + 1; /* e_xy+e_x > 0 or no 2nd y-step */
+  } while (x < 0);
+}
+
+void algo_arc(int xm, int ym, double sa, double ea, int r, void* data, AlgoPixel proc)
+{
+  int sx = std::cos(sa) * r;
+  int ex = std::cos(ea) * r;
+
+  int startQuadrant;
+  if (sa <= 0 && sa > -PI / 2) {
+    startQuadrant = 4;
+  }
+  else if (sa <= -PI / 2 && sa >= -PI) {
+    startQuadrant = 3;
+  }
+  else if (sa > 0 && sa < PI / 2) {
+    startQuadrant = 1;
+  }
+  else {
+    startQuadrant = 2;
+  }
+
+  int endQuadrant;
+  if (ea <= 0 && ea > -PI / 2) {
+    endQuadrant = 4;
+  }
+  else if (ea <= -PI / 2 && ea >= -PI) {
+    endQuadrant = 3;
+  }
+  else if (ea > 0 && ea < PI / 2) {
+    endQuadrant = 1;
+  }
+  else {
+    endQuadrant = 2;
+  }
+
+  // If start angle and end angle falls in the same quadrant we have to determine
+  // if we have to include the other quadrants or not since the arc is determined
+  // from start angle to end angle in clockwise direction.
+  bool includeQuadrant[4] = { false, false, false, false };
+  if (startQuadrant == endQuadrant) {
+    // If start angle is greater than end angle, include all quadrants for drawing
+    if (sa > ea) {
+      includeQuadrant[0] = true;
+      includeQuadrant[1] = true;
+      includeQuadrant[2] = true;
+      includeQuadrant[3] = true;
+    }
+    else {
+      // start angle is less to or equal to end angle then only include one quadrant
+      // for drawing.
+      includeQuadrant[startQuadrant - 1] = true;
+    }
+  }
+  else {
+    for (int i = startQuadrant - 1; i < startQuadrant - 1 + 4; ++i) {
+      int q = i % 4;
+      includeQuadrant[q] = true;
+      if (q == endQuadrant - 1)
+        break;
+    }
+  }
+
+  int x = -r, y = 0, err = 2 - 2 * r; /* II. Quadrant */
+  do {
+    if (includeQuadrant[0]) {
+      if ((startQuadrant != 1 && endQuadrant != 1) ||
+          (startQuadrant == 1 && endQuadrant != 1 && -x <= sx) ||
+          (startQuadrant != 1 && endQuadrant == 1 && -x >= ex) ||
+          (startQuadrant == 1 && endQuadrant == 1 &&
+           ((sa <= ea && -x <= sx && -x >= ex) || (sa > ea && (-x <= sx || -x >= ex)))))
+        proc(xm - x, ym + y, data); /*   I. Quadrant */
+    }
+
+    if (includeQuadrant[1]) {
+      if ((startQuadrant != 2 && endQuadrant != 2) ||
+          (startQuadrant == 2 && endQuadrant != 2 && -y <= sx) ||
+          (startQuadrant != 2 && endQuadrant == 2 && -y >= ex) ||
+          (startQuadrant == 2 && endQuadrant == 2 &&
+           ((sa <= ea && -y <= sx && -y >= ex) || (sa > ea && (-y <= sx || -y >= ex)))))
+        proc(xm - y, ym - x, data); /*  II. Quadrant */
+    }
+
+    if (includeQuadrant[2]) {
+      if ((startQuadrant != 3 && endQuadrant != 3) ||
+          (startQuadrant == 3 && endQuadrant != 3 && x >= sx) ||
+          (startQuadrant != 3 && endQuadrant == 3 && x <= ex) ||
+          (startQuadrant == 3 && endQuadrant == 3 &&
+           ((sa <= ea && -x <= -sx && -x >= -ex) || (sa > ea && (-x <= -sx || -x >= -ex)))))
+        proc(xm + x, ym - y, data); /* III. Quadrant */
+    }
+
+    if (includeQuadrant[3]) {
+      if ((startQuadrant != 4 && endQuadrant != 4) ||
+          (startQuadrant == 4 && endQuadrant != 4 && y >= sx) ||
+          (startQuadrant != 4 && endQuadrant == 4 && y <= ex) ||
+          (startQuadrant == 4 && endQuadrant == 4 &&
+           ((sa <= ea && y >= sx && y <= ex) || (sa > ea && (y >= sx || y <= ex)))))
+        proc(xm + y, ym + x, data); /*  IV. Quadrant */
+    }
+
+    r = err;
+    if (r <= y)
+      err += ++y * 2 + 1; /* e_xy+e_y < 0 */
+    if (r > x || err > y)
+      err += ++x * 2 + 1; /* e_xy+e_x > 0 or no 2nd y-step */
+  } while (x < 0);
+}
+
 static int adjust_ellipse_args(int& x0, int& y0, int& x1, int& y1, int& hPixels, int& vPixels)
 {
   // hPixels : straight horizontal pixels added to mid region of the ellipse.

src/doc/algo.h

@@ -48,6 +48,12 @@ void algo_line_continuous_with_fix_for_line_brush(int x1,
                                                   void* data,
                                                   AlgoPixel proc);
 
+void algo_circle(int xm, int ym, int sx, int sy, int r, void* data, AlgoPixel proc);
+
+void algo_circlefill(int xm, int ym, int sx, int sy, int r, void* data, AlgoHLine proc);
+
+void algo_arc(int xm, int ym, double sa, double ea, int r, void* data, AlgoPixel proc);
+
 void algo_ellipse(int x1,
                   int y1,
                   int x2,