Make GLFW_DOUBLEBUFFER a window attribute

README.md

@@ -130,6 +130,7 @@ information on what to include when reporting a bug.
  - Added `GLFW_X11_XCB_VULKAN_SURFACE` init hint for selecting X11 Vulkan
    surface extension (#1793)
  - Made joystick subsystem initialize at first use (#1284,#1646)
+ - Made `GLFW_DOUBLEBUFFER` a read-only window attribute
  - Updated the minimum required CMake version to 3.1
  - Disabled tests and examples by default when built as a CMake subdirectory
  - Bugfix: The CMake config-file package used an absolute path and was not

docs/window.dox

@@ -310,6 +310,7 @@ rendering will be disabled.
 always have sRGB rendering enabled.
 
 @anchor GLFW_DOUBLEBUFFER
+@anchor GLFW_DOUBLEBUFFER_hint
 __GLFW_DOUBLEBUFFER__ specifies whether the framebuffer should be double
 buffered.  You nearly always want to use double buffering.  This is a hard
 constraint.  Possible values are `GLFW_TRUE` and `GLFW_FALSE`.
@@ -1377,9 +1378,11 @@ if the window's context supports robustness, or `GLFW_NO_ROBUSTNESS` otherwise.
 
 @subsubsection window_attribs_fb Framebuffer related attributes
 
-GLFW does not expose attributes of the default framebuffer (i.e. the framebuffer
-attached to the window) as these can be queried directly with either OpenGL,
-OpenGL ES or Vulkan.
+GLFW does not expose most attributes of the default framebuffer (i.e. the
+framebuffer attached to the window) as these can be queried directly with either
+OpenGL, OpenGL ES or Vulkan.  The one exception is
+[GLFW_DOUBLEBUFFER](@ref GLFW_DOUBLEBUFFER_attrib), as this is not provided by
+OpenGL ES.
 
 If you are using version 3.0 or later of OpenGL or OpenGL ES, the
 `glGetFramebufferAttachmentParameteriv` function can be used to retrieve the
@@ -1405,6 +1408,11 @@ alpha sizes are queried from the `GL_BACK_LEFT`, while the depth and stencil
 sizes are queried from the `GL_DEPTH` and `GL_STENCIL` attachments,
 respectively.
 
+@anchor GLFW_DOUBLEBUFFER_attrib
+__GLFW_DOUBLEBUFFER__ indicates whether the specified window is double-buffered
+when rendering with OpenGL or OpenGL ES.  This can be set before creation with
+the [GLFW_DOUBLEBUFFER](@ref GLFW_DOUBLEBUFFER_hint) window hint.
+
 
 @section buffer_swap Buffer swapping
 

include/GLFW/glfw3.h

@@ -978,9 +978,10 @@ extern "C" {
  *  Monitor refresh rate [hint](@ref GLFW_REFRESH_RATE).
  */
 #define GLFW_REFRESH_RATE           0x0002100F
-/*! @brief Framebuffer double buffering hint.
+/*! @brief Framebuffer double buffering hint and attribute.
  *
- *  Framebuffer double buffering [hint](@ref GLFW_DOUBLEBUFFER).
+ *  Framebuffer double buffering [hint](@ref GLFW_DOUBLEBUFFER_hint) and
+ *  [attribute](@ref GLFW_DOUBLEBUFFER_attrib).
  */
 #define GLFW_DOUBLEBUFFER           0x00021010
 

src/internal.h

@@ -387,6 +387,7 @@ struct _GLFWwindow
     GLFWbool            mousePassthrough;
     GLFWbool            shouldClose;
     void*               userPointer;
+    GLFWbool            doublebuffer;
     GLFWvidmode         videoMode;
     _GLFWmonitor*       monitor;
     _GLFWcursor*        cursor;

src/window.c

@@ -206,6 +206,8 @@ GLFWAPI GLFWwindow* glfwCreateWindow(int width, int height,
     window->mousePassthrough = wndconfig.mousePassthrough;
     window->cursorMode       = GLFW_CURSOR_NORMAL;
 
+    window->doublebuffer = fbconfig.doublebuffer;
+
     window->minwidth    = GLFW_DONT_CARE;
     window->minheight   = GLFW_DONT_CARE;
     window->maxwidth    = GLFW_DONT_CARE;
@@ -841,6 +843,8 @@ GLFWAPI int glfwGetWindowAttrib(GLFWwindow* handle, int attrib)
             return window->floating;
         case GLFW_AUTO_ICONIFY:
             return window->autoIconify;
+        case GLFW_DOUBLEBUFFER:
+            return window->doublebuffer;
         case GLFW_CLIENT_API:
             return window->context.client;
         case GLFW_CONTEXT_CREATION_API: