Win32: Filter out duplicate size events

This mirrors the filtering done on X11 and Cocoa.  Possibly this should
be done by shared code instead.

Fixes #1610.

README.md

@@ -158,6 +158,7 @@ information on what to include when reporting a bug.
  - [Win32] Bugfix: Monitor functions could return invalid values after
    configuration change (#1761)
  - [Win32] Bugfix: Initialization would segfault on Windows 8 (not 8.1) (#1775)
+ - [Win32] Bugfix: Duplicate size events were not filtered (#1610)
  - [Cocoa] Added support for `VK_EXT_metal_surface` (#1619)
  - [Cocoa] Added locating the Vulkan loader at runtime in an application bundle
  - [Cocoa] Moved main menu creation to GLFW initialization time (#1649)
@@ -326,6 +327,7 @@ skills.
  - Shane Liesegang
  - Anders Lindqvist
  - Leon Linhart
+ - Marco Lizza
  - Eyal Lotem
  - Aaron Loucks
  - Luflosi

src/win32_platform.h

@@ -314,6 +314,9 @@ typedef struct _GLFWwindowWin32
     GLFWbool            scaleToMonitor;
     GLFWbool            keymenu;
 
+    // Cached size used to filter out duplicate events
+    int                 width, height;
+
     // The last received cursor position, regardless of source
     int                 lastCursorPosX, lastCursorPosY;
     // The last recevied high surrogate when decoding pairs of UTF-16 messages

src/win32_window.c

@@ -961,6 +961,8 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
 
         case WM_SIZE:
         {
+            const int width = LOWORD(lParam);
+            const int height = HIWORD(lParam);
             const GLFWbool iconified = wParam == SIZE_MINIMIZED;
             const GLFWbool maximized = wParam == SIZE_MAXIMIZED ||
                                        (window->win32.maximized &&
@@ -975,8 +977,14 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
             if (window->win32.maximized != maximized)
                 _glfwInputWindowMaximize(window, maximized);
 
-            _glfwInputFramebufferSize(window, LOWORD(lParam), HIWORD(lParam));
+            if (width != window->win32.width || height != window->win32.height)
-            _glfwInputWindowSize(window, LOWORD(lParam), HIWORD(lParam));
+            {
+                window->win32.width = width;
+                window->win32.height = height;
+
+                _glfwInputFramebufferSize(window, width, height);
+                _glfwInputWindowSize(window, width, height);
+            }
 
             if (window->monitor && window->win32.iconified != iconified)
             {
@@ -1315,6 +1323,8 @@ static int createNativeWindow(_GLFWwindow* window,
         window->win32.transparent = GLFW_TRUE;
     }
 
+    _glfwPlatformGetWindowSize(window, &window->win32.width, &window->win32.height);
+
     return GLFW_TRUE;
 }