Add GLFW_SCALE_TO_MONITOR

This adds the GLFW_SCALE_TO_MONITOR window hint for automatically
resizing the content area of a window to the requested size times the
monitor content scale each time it is placed on a new monitor.  This
only applies to windowed mode windows and includes the initial placement
at window creation.

This hint only has an effect on platforms where screen coordinates and
pixels always map 1:1 such as Windows and X11.  Platforms like macOS
instead change the resolution of the framebuffer independently of the
window size.

Related to #676.
Related to #1115.

docs/news.dox

@@ -73,6 +73,10 @@ glfwGetWindowContentScale and @ref glfwGetMonitorContentScale.
 Changes of the content scale of a window can be received with the window content
 scale callback, set with @ref glfwSetWindowContentScaleCallback.
 
+The @ref GLFW_SCALE_TO_MONITOR window hint enables automatic resizing of a
+window by the content scale of the monitor it is placed, on platforms like
+Windows and X11 where this is necessary.
+
 @see @ref window_scale
 
 

docs/window.dox

@@ -238,6 +238,17 @@ does not affect window decorations.  Possible values are `GLFW_TRUE` and
 __GLFW_FOCUS_ON_SHOW__ specifies whether the window will be given input
 focus when @ref glfwShowWindow is called. Possible values are `GLFW_TRUE` and `GLFW_FALSE`.
 
+@anchor GLFW_SCALE_TO_MONITOR
+__GLFW_SCALE_TO_MONITOR__ specified whether the window content area should be
+resized based on the [monitor content scale](@ref monitor_scale) of any monitor
+it is placed on.  This includes the initial placement when the window is
+created.  Possible values are `GLFW_TRUE` and `GLFW_FALSE`.
+
+This hint only has an effect on platforms where screen coordinates and pixels
+always map 1:1 such as Windows and X11.  On platforms like macOS the resolution
+of the framebuffer is changed independently of the window size.
+
+
 @subsubsection window_hints_fb Framebuffer related hints
 
 @anchor GLFW_RED_BITS
@@ -493,6 +504,7 @@ GLFW_MAXIMIZED                | `GLFW_FALSE`                | `GLFW_TRUE` or `GL
 GLFW_CENTER_CURSOR            | `GLFW_TRUE`                 | `GLFW_TRUE` or `GLFW_FALSE`
 GLFW_TRANSPARENT_FRAMEBUFFER  | `GLFW_FALSE`                | `GLFW_TRUE` or `GLFW_FALSE`
 GLFW_FOCUS_ON_SHOW            | `GLFW_TRUE`                 | `GLFW_TRUE` or `GLFW_FALSE`
+GLFW_SCALE_TO_MONITOR         | `GLFW_FALSE`                | `GLFW_TRUE` or `GLFW_FALSE`
 GLFW_RED_BITS                 | 8                           | 0 to `INT_MAX` or `GLFW_DONT_CARE`
 GLFW_GREEN_BITS               | 8                           | 0 to `INT_MAX` or `GLFW_DONT_CARE`
 GLFW_BLUE_BITS                | 8                           | 0 to `INT_MAX` or `GLFW_DONT_CARE`
@@ -716,6 +728,12 @@ void window_content_scale_callback(GLFWwindow* window, float xscale, float yscal
 }
 @endcode
 
+On platforms where pixels and screen coordinates always map 1:1, the window
+will need to be resized to appear the same size when it is moved to a monitor
+with a different content scale.  To have this done automatically both when the
+window is created and when its content scale later changes, set the @ref
+GLFW_SCALE_TO_MONITOR window hint.
+
 
 @subsection window_sizelimits Window size limits
 

include/GLFW/glfw3.h

@@ -973,6 +973,10 @@ extern "C" {
  *  [attribute](@ref GLFW_CLIENT_API_attrib).
  */
 #define GLFW_CONTEXT_CREATION_API   0x0002200B
+/*! @brief Window content area scaling window
+ *  [window hint](@ref GLFW_SCALE_TO_MONITOR).
+ */
+#define GLFW_SCALE_TO_MONITOR       0x0002200C
 
 #define GLFW_COCOA_RETINA_FRAMEBUFFER 0x00023001
 #define GLFW_COCOA_FRAME_NAME         0x00023002

src/internal.h

@@ -268,6 +268,7 @@ struct _GLFWwndconfig
     GLFWbool      maximized;
     GLFWbool      centerCursor;
     GLFWbool      focusOnShow;
+    GLFWbool      scaleToMonitor;
     struct {
         GLFWbool  retina;
         char      frameName[256];

src/win32_platform.h

@@ -306,6 +306,7 @@ typedef struct _GLFWwindowWin32
     GLFWbool            maximized;
     // Whether to enable framebuffer transparency on DWM
     GLFWbool            transparent;
+    GLFWbool            scaleToMonitor;
 
     // The last received cursor position, regardless of source
     int                 lastCursorPosX, lastCursorPosY;

src/win32_window.c

@@ -1063,6 +1063,9 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
 
         case WM_GETDPISCALEDSIZE:
         {
+            if (window->win32.scaleToMonitor)
+                break;
+
             // Adjust the window size to keep the client area size constant
             if (_glfwIsWindows10CreatorsUpdateOrGreaterWin32())
             {
@@ -1230,15 +1233,34 @@ static int createNativeWindow(_GLFWwindow* window,
                                     WM_COPYGLOBALDATA, MSGFLT_ALLOW, NULL);
     }
 
-    // Adjust window size to account for the DPI scaled window frame
+    window->win32.scaleToMonitor = wndconfig->scaleToMonitor;
+
+    // Adjust window size to account for DPI scaling of the window frame and
+    // optionally DPI scaling of the client area
     // This cannot be done until we know what monitor it was placed on
-    if (_glfwIsWindows10AnniversaryUpdateOrGreaterWin32() && !window->monitor)
+    if (!window->monitor)
     {
         RECT rect = { 0, 0, wndconfig->width, wndconfig->height };
+
+        if (wndconfig->scaleToMonitor)
+        {
+            float xscale, yscale;
+            _glfwPlatformGetWindowContentScale(window, &xscale, &yscale);
+            rect.right = (int) (rect.right * xscale);
+            rect.bottom = (int) (rect.bottom * yscale);
+        }
+
         ClientToScreen(window->win32.handle, (POINT*) &rect.left);
         ClientToScreen(window->win32.handle, (POINT*) &rect.right);
+
+        if (_glfwIsWindows10AnniversaryUpdateOrGreaterWin32())
+        {
             AdjustWindowRectExForDpi(&rect, style, FALSE, exStyle,
                                      GetDpiForWindow(window->win32.handle));
+        }
+        else
+            AdjustWindowRectEx(&rect, style, FALSE, exStyle);
+
         SetWindowPos(window->win32.handle, NULL,
                      rect.left, rect.top,
                      rect.right - rect.left, rect.bottom - rect.top,

src/window.c

@@ -369,6 +369,9 @@ GLFWAPI void glfwWindowHint(int hint, int value)
         case GLFW_COCOA_GRAPHICS_SWITCHING:
             _glfw.hints.context.nsgl.offline = value ? GLFW_TRUE : GLFW_FALSE;
             return;
+        case GLFW_SCALE_TO_MONITOR:
+            _glfw.hints.window.scaleToMonitor = value ? GLFW_TRUE : GLFW_FALSE;
+            return;
         case GLFW_CENTER_CURSOR:
             _glfw.hints.window.centerCursor = value ? GLFW_TRUE : GLFW_FALSE;
             return;

src/x11_window.c

@@ -592,6 +592,15 @@ static GLFWbool createNativeWindow(_GLFWwindow* window,
                                    const _GLFWwndconfig* wndconfig,
                                    Visual* visual, int depth)
 {
+    int width = wndconfig->width;
+    int height = wndconfig->height;
+
+    if (wndconfig->scaleToMonitor)
+    {
+        width *= _glfw.x11.contentScaleX;
+        height *= _glfw.x11.contentScaleY;
+    }
+
     // Create a colormap based on the visual used by the current context
     window->x11.colormap = XCreateColormap(_glfw.x11.display,
                                            _glfw.x11.root,
@@ -617,7 +626,7 @@ static GLFWbool createNativeWindow(_GLFWwindow* window,
         window->x11.handle = XCreateWindow(_glfw.x11.display,
                                            _glfw.x11.root,
                                            0, 0,
-                                           wndconfig->width, wndconfig->height,
+                                           width, height,
                                            0,      // Border width
                                            depth,  // Color depth
                                            InputOutput,
@@ -720,7 +729,7 @@ static GLFWbool createNativeWindow(_GLFWwindow* window,
         XFree(hints);
     }
 
-    updateNormalHints(window, wndconfig->width, wndconfig->height);
+    updateNormalHints(window, width, height);
 
     // Set ICCCM WM_CLASS property
     {

tests/gamma.c

@@ -99,6 +99,8 @@ int main(int argc, char** argv)
 
     monitor = glfwGetPrimaryMonitor();
 
+    glfwWindowHint(GLFW_SCALE_TO_MONITOR, GLFW_TRUE);
+
     window = glfwCreateWindow(800, 400, "Gamma Test", NULL, NULL);
     if (!window)
     {

tests/inputlag.c

@@ -200,6 +200,8 @@ int main(int argc, char** argv)
     glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
     glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
 
+    glfwWindowHint(GLFW_SCALE_TO_MONITOR, GLFW_TRUE);
+
     window = glfwCreateWindow(width, height, "Input lag test", monitor, NULL);
     if (!window)
     {

tests/joysticks.c

@@ -180,6 +180,8 @@ int main(void)
     if (!glfwInit())
         exit(EXIT_FAILURE);
 
+    glfwWindowHint(GLFW_SCALE_TO_MONITOR, GLFW_TRUE);
+
     window = glfwCreateWindow(800, 600, "Joystick Test", NULL, NULL);
     if (!window)
     {

tests/opacity.c

@@ -57,6 +57,8 @@ int main(int argc, char** argv)
     if (!glfwInit())
         exit(EXIT_FAILURE);
 
+    glfwWindowHint(GLFW_SCALE_TO_MONITOR, GLFW_TRUE);
+
     window = glfwCreateWindow(400, 400, "Opacity", NULL, NULL);
     if (!window)
     {