A very jank circle algorithm that overdraws many of the lines but mostly works.

matrix.cpp

@@ -179,6 +179,58 @@ namespace matrix {
     }
   }
 
+
+  circle::circle(Point center, int radius) :
+    center(center), radius(radius)
+  {
+    xi = 0;
+    yi = radius;
+    m = 5 - 4 * radius;
+    step = 0;
+  }
+
+  void circle::update() {
+    if(m > 0) {
+      yi--;
+      m -= 8 * yi;
+    }
+    xi++;
+    m += 8 * xi + 4;
+  }
+
+  bool circle::next() {
+    if(xi <= yi) {
+      switch(step % 4) {
+        case 0:
+          x0 = center.x - xi;
+          y = center.y - yi;
+          x1 = center.x + xi;
+          break;
+        case 1:
+          x0 = center.x - yi;
+          y = center.y - xi;
+          x1 = center.x + yi;
+          break;
+        case 2:
+          x0 = center.x - yi;
+          y = center.y + xi;
+          x1 = center.x + yi;
+          break;
+        case 3:
+          x0 = center.x - xi;
+          y = center.y + yi;
+          x1 = center.x + xi;
+          update();
+          break;
+      }
+
+      step++;
+      return true;
+    } else {
+      return false;
+    }
+  }
+
   void dump(const std::string &msg, Matrix &map, int show_x, int show_y) {
     println("----------------- {}", msg);