Add support for HiDPI modes

When HiDPI is enabled, the size of the OpenGL surface (specified in
pixels) may no longer correspond to the size of the window (specified
in points). Width, Height, ClientSize and ClientRectangle return the
size of the OpenGL surface in device-dependent pixel coordinates
(origin: top-left pixel of the surface). Bounds and Size return the
size of the window in device-independent point coordinates (origin:
desktop).

Source/OpenTK/NativeWindow.cs

@@ -192,8 +192,10 @@ namespace OpenTK
         #region Bounds
 
         /// <summary>
-        /// Gets or sets a <see cref="System.Drawing.Rectangle"/> structure that contains the external bounds of this window, in screen coordinates.
+        /// Gets or sets a <see cref="System.Drawing.Rectangle"/> structure
-        /// External bounds include the title bar, borders and drawing area of the window.
+        /// that specifies the external bounds of this window, in screen coordinates.
+        /// The coordinates are specified in device-independent points and
+        /// include the title bar, borders and drawing area of the window.
         /// </summary>
         public Rectangle Bounds
         {
@@ -214,8 +216,9 @@ namespace OpenTK
         #region ClientRectangle
 
         /// <summary>
-        /// Gets or sets a <see cref="System.Drawing.Rectangle"/> structure that contains the internal bounds of this window, in client coordinates.
+        /// Gets or sets a <see cref="System.Drawing.Rectangle"/> structure
-        /// The internal bounds include the drawing area of the window, but exclude the titlebar and window borders.
+        /// that defines the bounds of the OpenGL surface, in window coordinates.
+        /// The coordinates are specified in device-dependent pixels.
         /// </summary>
         public Rectangle ClientRectangle
         {
@@ -236,7 +239,9 @@ namespace OpenTK
         #region ClientSize
 
         /// <summary>
-        /// Gets or sets a <see cref="System.Drawing.Size"/> structure that contains the internal size this window.
+        /// Gets or sets a <see cref="System.Drawing.Size"/> structure
+        /// that defines the size of the OpenGL surface in window coordinates.
+        /// The coordinates are specified in device-dependent pixels.
         /// </summary>
         public Size ClientSize
         {
@@ -288,7 +293,8 @@ namespace OpenTK
         #region Height
 
         /// <summary>
-        /// Gets or sets the external height of this window.
+        /// Gets or sets the height of the OpenGL surface in window coordinates.
+        /// The coordinates are specified in device-dependent pixels.
         /// </summary>
         public int Height
         {
@@ -431,7 +437,8 @@ namespace OpenTK
         #region Width
 
         /// <summary>
-        /// Gets or sets the external width of this window.
+        /// Gets or sets the height of the OpenGL surface in window coordinates.
+        /// The coordinates are specified in device-dependent pixels.
         /// </summary>
         public int Width
         {
@@ -506,7 +513,8 @@ namespace OpenTK
         #region X
 
         /// <summary>
-        /// Gets or sets the horizontal location of this window on the desktop.
+        /// Gets or sets the horizontal location of this window in screen coordinates.
+        /// The coordinates are specified in device-independent points.
         /// </summary>
         public int X
         {
@@ -527,7 +535,8 @@ namespace OpenTK
         #region Y
 
         /// <summary>
-        /// Gets or sets the vertical location of this window on the desktop.
+        /// Gets or sets the vertical location of this window in screen coordinates.
+        /// The coordinates are specified in device-independent points.
         /// </summary>
         public int Y
         {

Source/OpenTK/Platform/SDL2/Sdl2NativeWindow.cs

@@ -75,6 +75,7 @@ namespace OpenTK.Platform.SDL2
                 flags |= SDL.SDL_WindowFlags.SDL_WINDOW_OPENGL;
                 flags |= SDL.SDL_WindowFlags.SDL_WINDOW_RESIZABLE;
                 flags |= SDL.SDL_WindowFlags.SDL_WINDOW_HIDDEN;
+                flags |= SDL.SDL_WindowFlags.SDL_WINDOW_ALLOW_HIGHDPI;
 
                 if ((flags & SDL.SDL_WindowFlags.SDL_WINDOW_FULLSCREEN_DESKTOP) != 0 ||
                     (flags & SDL.SDL_WindowFlags.SDL_WINDOW_FULLSCREEN) != 0)
@@ -249,7 +250,9 @@ namespace OpenTK.Platform.SDL2
 
         static void ProcessMotionEvent(Sdl2NativeWindow window, SDL.SDL_Event ev)
         {
-                window.mouse.Position = new Point(ev.motion.x, ev.motion.y);
+            float scale = window.ClientSize.Width / (float)window.Size.Width;
+            window.mouse.Position = new Point(
+                (int)(ev.motion.x * scale), (int)(ev.motion.y * scale));
         }
 
         static void ProcessWheelEvent(Sdl2NativeWindow window, SDL.SDL_Event ev)
@@ -779,11 +782,11 @@ namespace OpenTK.Platform.SDL2
         {
             get
             {
-                return Size.Width;
+                return ClientSize.Width;
             }
             set
             {
-                Size = new Size(value, Height);
+                ClientSize = new Size(value, Height);
             }
         }
 
@@ -791,11 +794,11 @@ namespace OpenTK.Platform.SDL2
         {
             get
             {
-                return Size.Height;
+                return ClientSize.Height;
             }
             set
             {
-                Size = new Size(Width, value);
+                ClientSize = new Size(Width, value);
             }
         }
 
@@ -803,15 +806,11 @@ namespace OpenTK.Platform.SDL2
         {
             get
             {
-                // Todo: SDL2 does not have any APIs to get
+                return new Rectangle(new Point(), ClientSize);
-                // the border size or the bounds of the window
-                // (everything is defined in terms of the client
-                // area)
-                return Bounds;
             }
             set
             {
-                Bounds = value;
+                ClientSize = value.Size;
             }
         }
 
@@ -819,11 +818,14 @@ namespace OpenTK.Platform.SDL2
         {
             get
             {
-                return Size;
+                int w, h;
+                SDL.SDL_GL_GetDrawableSize(window.Handle, out w, out h);
+                return new Size(w, h);
             }
             set
             {
-                Size = value;
+                float scale = Size.Width / (float)ClientSize.Width;
+                Size = new Size((int)(value.Width * scale), (int)(value.Height * scale));
             }
         }
 

Source/OpenTK/Platform/SDL2/sdl2-cs/src/SDL2.cs

@@ -960,6 +960,7 @@ namespace OpenTK.Platform.SDL2
 			SDL_WINDOW_FULLSCREEN_DESKTOP =
 				(SDL_WINDOW_FULLSCREEN | 0x00001000),
 			SDL_WINDOW_FOREIGN =		0x00000800,
+            SDL_WINDOW_ALLOW_HIGHDPI = 0x00002000,
 		}
 		
 		public const int SDL_WINDOWPOS_UNDEFINED_MASK =	0x1FFF0000;
@@ -1341,7 +1342,10 @@ namespace OpenTK.Platform.SDL2
 		/* context refers to an SDL_GLContext */
 		[DllImport(nativeLibName, CallingConvention = CallingConvention.Cdecl)]
 		public static extern void SDL_GL_DeleteContext(IntPtr context);
-		
+
+        [DllImport(nativeLibName, CallingConvention = CallingConvention.Cdecl)]
+        public static extern void SDL_GL_GetDrawableSize(IntPtr window, out int w, out int h);
+
 		/* IntPtr refers to a function pointer */
 		[DllImport(nativeLibName, CallingConvention = CallingConvention.Cdecl)]
 		public static extern IntPtr SDL_GL_GetProcAddress(