桌面环境：增加环境变量APP并给Paint应用程序增加更多画图工具

Gui/Apps/Paint/Tools/FilledCircleTool.cs

@@ -0,0 +1,58 @@
+using Cosmos.System;
+using System;
+
+namespace CMLeonOS.Gui.Apps.Paint.Tools
+{
+    internal class FilledCircleTool : Tool
+    {
+        public FilledCircleTool() : base("Filled Circle")
+        {
+        }
+
+        private bool started;
+        private int startX;
+        private int startY;
+
+        internal override void Run(Paint paint, Window canvas, MouseState mouseState, int mouseX, int mouseY)
+        {
+            if (mouseState == MouseState.Left)
+            {
+                if (!started)
+                {
+                    started = true;
+                    startX = mouseX;
+                    startY = mouseY;
+                }
+            }
+            else if (started)
+            {
+                int radiusX = Math.Abs(mouseX - startX);
+                int radiusY = Math.Abs(mouseY - startY);
+                int radius = Math.Max(radiusX, radiusY);
+
+                for (int y = -radius; y <= radius; y++)
+                {
+                    for (int x = -radius; x <= radius; x++)
+                    {
+                        if ((x * x) + (y * y) <= radius * radius)
+                        {
+                            int drawX = startX + x;
+                            int drawY = startY + y;
+                            if (paint.IsInBounds(drawX, drawY))
+                            {
+                                canvas.DrawPoint(drawX, drawY, paint.SelectedColor);
+                            }
+                        }
+                    }
+                }
+
+                started = false;
+            }
+        }
+
+        internal override void Deselected()
+        {
+            started = false;
+        }
+    }
+}