Add glfwSetWindowContentScaleCallback

Related to #677.
Related to #1115.

src/cocoa_platform.h

@@ -88,9 +88,10 @@ typedef struct _GLFWwindowNS
 
     GLFWbool        maximized;
 
-    // Cached window and framebuffer sizes used to filter out duplicate events
+    // Cached window properties to filter out duplicate events
     int             width, height;
     int             fbWidth, fbHeight;
+    float           xscale, yscale;
 
     // The total sum of the distances the cursor has been warped
     // since the last cursor motion event was processed

src/cocoa_window.m

@@ -574,6 +574,16 @@ static const NSRange kEmptyRange = { NSNotFound, 0 };
         window->ns.fbHeight = fbRect.size.height;
         _glfwInputFramebufferSize(window, fbRect.size.width, fbRect.size.height);
     }
+
+    const float xscale = fbRect.size.width / contentRect.size.width;
+    const float yscale = fbRect.size.height / contentRect.size.height;
+
+    if (xscale != window->ns.xscale || yscale != window->ns.yscale)
+    {
+        window->ns.xscale = xscale;
+        window->ns.yscale = yscale;
+        _glfwInputWindowContentScale(window, xscale, yscale);
+    }
 }
 
 - (void)drawRect:(NSRect)rect

src/internal.h

@@ -437,6 +437,7 @@ struct _GLFWwindow
         GLFWwindowiconifyfun    iconify;
         GLFWwindowmaximizefun   maximize;
         GLFWframebuffersizefun  fbsize;
+        GLFWwindowcontentscalefun scale;
         GLFWmousebuttonfun      mouseButton;
         GLFWcursorposfun        cursorPos;
         GLFWcursorenterfun      cursorEnter;
@@ -754,6 +755,14 @@ void _glfwInputWindowSize(_GLFWwindow* window, int width, int height);
  */
 void _glfwInputFramebufferSize(_GLFWwindow* window, int width, int height);
 
+/*! @brief Notifies shared code that a window content scale has changed.
+ *  @param[in] window The window that received the event.
+ *  @param[in] xscale The new x-axis content scale of the window.
+ *  @param[in] yscale The new y-axis content scale of the window.
+ *  @ingroup event
+ */
+void _glfwInputWindowContentScale(_GLFWwindow* window, float xscale, float yscale);
+
 /*! @brief Notifies shared code that a window has been iconified or restored.
  *  @param[in] window The window that received the event.
  *  @param[in] iconified `GLFW_TRUE` if the window was iconified, or

src/win32_window.c

@@ -996,6 +996,14 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
             return 0;
         }
 
+        case WM_DPICHANGED:
+        {
+            const float xscale = HIWORD(wParam) / 96.f;
+            const float yscale = LOWORD(wParam) / 96.f;
+            _glfwInputWindowContentScale(window, xscale, yscale);
+            break;
+        }
+
         case WM_SETCURSOR:
         {
             if (LOWORD(lParam) == HTCLIENT)

src/window.c

@@ -94,6 +94,12 @@ void _glfwInputFramebufferSize(_GLFWwindow* window, int width, int height)
         window->callbacks.fbsize((GLFWwindow*) window, width, height);
 }
 
+void _glfwInputWindowContentScale(_GLFWwindow* window, float xscale, float yscale)
+{
+    if (window->callbacks.scale)
+        window->callbacks.scale((GLFWwindow*) window, xscale, yscale);
+}
+
 void _glfwInputWindowDamage(_GLFWwindow* window)
 {
     if (window->callbacks.refresh)
@@ -1013,6 +1019,17 @@ GLFWAPI GLFWframebuffersizefun glfwSetFramebufferSizeCallback(GLFWwindow* handle
     return cbfun;
 }
 
+GLFWAPI GLFWwindowcontentscalefun glfwSetWindowContentScaleCallback(GLFWwindow* handle,
+                                                                    GLFWwindowcontentscalefun cbfun)
+{
+    _GLFWwindow* window = (_GLFWwindow*) handle;
+    assert(window != NULL);
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+    _GLFW_SWAP_POINTERS(window->callbacks.scale, cbfun);
+    return cbfun;
+}
+
 GLFWAPI void glfwPollEvents(void)
 {
     _GLFW_REQUIRE_INIT();