Add ability to clear Depth and Stencil

osu.Framework/Graphics/Containers/BufferedContainerDrawNode.cs

···
                 // We can do this by adding a translation component to our (orthogonal) projection matrix.
                 GLWrapper.PushOrtho(ScreenSpaceDrawRectangle);
 
-                GLWrapper.ClearColour(BackgroundColour);
+                GLWrapper.Clear(new ClearInfo(BackgroundColour));
                 base.Draw(vertexAction);
 
                 GLWrapper.PopOrtho();

osu.Framework/Graphics/OpenGL/ClearInfo.cs

···
+// Copyright (c) ppy Pty Ltd <[e-mail]>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osuTK.Graphics;
+
+namespace osu.Framework.Graphics.OpenGL
+{
+    /// <summary>
+    /// Information for how the current frame buffer should be cleared.
+    /// </summary>
+    public readonly struct ClearInfo
+    {
+        /// <summary>
+        /// The default clear properties, as defined by OpenGL.
+        /// </summary>
+        public static ClearInfo Default => new ClearInfo(default);
+
+        /// <summary>
+        /// The colour to write to the frame buffer.
+        /// </summary>
+        public readonly Color4 Colour;
+
+        /// <summary>
+        /// The depth to write to the frame buffer.
+        /// </summary>
+        public readonly double Depth;
+
+        /// <summary>
+        /// The stencil value to write to the frame buffer.
+        /// </summary>
+        public readonly int Stencil;
+
+        public ClearInfo(Color4 colour = default, double depth = 1f, int stencil = 0)
+        {
+            Colour = colour;
+            Depth = depth;
+            Stencil = stencil;
+        }
+    }
+}

osu.Framework/Graphics/OpenGL/GLWrapper.cs

···
                 BlendRange = 1,
                 AlphaExponent = 1,
             }, true);
+
+            Clear(ClearInfo.Default);
         }
 
-        // We initialize to an invalid value such that we are not missing an initial GL.ClearColor call.
-        private static Color4 clearColour = new Color4(-1, -1, -1, -1);
+        private static ClearInfo currentClearInfo;
 
-        public static void ClearColour(Color4 c)
+        public static void Clear(ClearInfo clearInfo)
         {
-            if (clearColour != c)
+            if (clearInfo.Colour != currentClearInfo.Colour)
+                GL.ClearColor(clearInfo.Colour);
+
+            if (clearInfo.Depth != currentClearInfo.Depth)
             {
-                clearColour = c;
-                GL.ClearColor(clearColour);
+                // Todo: Wtf. osuTK's bindings are broken for glClearDepthf(). Using glClearDepth() for now
+                osuTK.Graphics.OpenGL.GL.ClearDepth(clearInfo.Depth);
             }
 
+            if (clearInfo.Stencil != currentClearInfo.Stencil)
+                GL.ClearStencil(clearInfo.Stencil);
+
             GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit | ClearBufferMask.StencilBufferBit);
+
+            currentClearInfo = clearInfo;
         }
 
         /// <summary>

osu.Framework/Platform/GameHost.cs

···
             setVSyncMode();
 
             GLWrapper.Reset(new Vector2(Window.ClientSize.Width, Window.ClientSize.Height));
-            GLWrapper.ClearColour(Color4.Black);
+            GLWrapper.Clear(ClearInfo.Default);
         }
 
         private long lastDrawFrameId;
···
                     using (drawMonitor.BeginCollecting(PerformanceCollectionType.GLReset))
                     {
                         GLWrapper.Reset(new Vector2(Window.ClientSize.Width, Window.ClientSize.Height));
-                        GLWrapper.ClearColour(Color4.Black);
+                        GLWrapper.Clear(ClearInfo.Default);
                     }
 
                     buffer.Object.Draw(null);