Allow rendering during the modal resize loop on macOS

Fixes https://github.com/libsdl-org/SDL/issues/11508

src/video/SDL_sysvideo.h

@@ -568,6 +568,7 @@ extern void SDL_OnWindowMoved(SDL_Window *window);
 extern void SDL_OnWindowResized(SDL_Window *window);
 extern void SDL_CheckWindowPixelSizeChanged(SDL_Window *window);
 extern void SDL_OnWindowPixelSizeChanged(SDL_Window *window);
+extern void SDL_OnWindowLiveResizeUpdate(SDL_Window *window);
 extern void SDL_OnWindowMinimized(SDL_Window *window);
 extern void SDL_OnWindowMaximized(SDL_Window *window);
 extern void SDL_OnWindowRestored(SDL_Window *window);

src/video/SDL_video.c

@@ -35,6 +35,7 @@
 #include "../timer/SDL_timer_c.h"
 #include "../camera/SDL_camera_c.h"
 #include "../render/SDL_sysrender.h"
+#include "../main/SDL_main_callbacks.h"
 
 #ifdef SDL_VIDEO_OPENGL
 #include <SDL3/SDL_opengl.h>
@@ -3920,6 +3921,16 @@ void SDL_OnWindowPixelSizeChanged(SDL_Window *window)
     window->surface_valid = false;
 }
 
+void SDL_OnWindowLiveResizeUpdate(SDL_Window *window)
+{
+    if (SDL_HasMainCallbacks()) {
+        SDL_IterateMainCallbacks(false);
+    } else {
+        // Send an expose event so the application can redraw
+        SDL_SendWindowEvent(window, SDL_EVENT_WINDOW_EXPOSED, 0, 0);
+    }
+}
+
 static void SDL_CheckWindowSafeAreaChanged(SDL_Window *window)
 {
     SDL_Rect rect;

src/video/cocoa/SDL_cocoawindow.h

@@ -59,6 +59,7 @@ typedef enum
     NSInteger focusClickPending;
     float pendingWindowWarpX, pendingWindowWarpY;
     BOOL isDragAreaRunning;
+    NSTimer *liveResizeTimer;
 }
 
 - (BOOL)isTouchFromTrackpad:(NSEvent *)theEvent;
@@ -83,6 +84,9 @@ typedef enum
 // Window delegate functionality
 - (BOOL)windowShouldClose:(id)sender;
 - (void)windowDidExpose:(NSNotification *)aNotification;
+- (void)windowDidChangeOcclusionState:(NSNotification *)aNotification;
+- (void)windowWillStartLiveResize:(NSNotification *)aNotification;
+- (void)windowDidEndLiveResize:(NSNotification *)aNotification;
 - (void)windowDidMove:(NSNotification *)aNotification;
 - (void)windowDidResize:(NSNotification *)aNotification;
 - (void)windowDidMiniaturize:(NSNotification *)aNotification;

src/video/cocoa/SDL_cocoawindow.m

@@ -696,11 +696,15 @@ static NSCursor *Cocoa_GetDesiredCursor(void)
     isMiniaturizing = NO;
     isDragAreaRunning = NO;
     pendingWindowWarpX = pendingWindowWarpY = FLT_MAX;
+    liveResizeTimer = nil;
 
     center = [NSNotificationCenter defaultCenter];
 
     if ([window delegate] != nil) {
         [center addObserver:self selector:@selector(windowDidExpose:) name:NSWindowDidExposeNotification object:window];
+        [center addObserver:self selector:@selector(windowDidChangeOcclusionState:) name:NSWindowDidChangeOcclusionStateNotification object:window];
+        [center addObserver:self selector:@selector(windowWillStartLiveResize:) name:NSWindowWillStartLiveResizeNotification object:window];
+        [center addObserver:self selector:@selector(windowDidEndLiveResize:) name:NSWindowDidEndLiveResizeNotification object:window];
         [center addObserver:self selector:@selector(windowWillMove:) name:NSWindowWillMoveNotification object:window];
         [center addObserver:self selector:@selector(windowDidMove:) name:NSWindowDidMoveNotification object:window];
         [center addObserver:self selector:@selector(windowDidResize:) name:NSWindowDidResizeNotification object:window];
@@ -718,7 +722,6 @@ static NSCursor *Cocoa_GetDesiredCursor(void)
         [center addObserver:self selector:@selector(windowDidExitFullScreen:) name:NSWindowDidExitFullScreenNotification object:window];
         [center addObserver:self selector:@selector(windowDidFailToEnterFullScreen:) name:@"NSWindowDidFailToEnterFullScreenNotification" object:window];
         [center addObserver:self selector:@selector(windowDidFailToExitFullScreen:) name:@"NSWindowDidFailToExitFullScreenNotification" object:window];
-        [center addObserver:self selector:@selector(windowDidChangeOcclusionState:) name:NSWindowDidChangeOcclusionStateNotification object:window];
     } else {
         [window setDelegate:self];
     }
@@ -853,6 +856,9 @@ static NSCursor *Cocoa_GetDesiredCursor(void)
 
     if ([window delegate] != self) {
         [center removeObserver:self name:NSWindowDidExposeNotification object:window];
+        [center removeObserver:self name:NSWindowDidChangeOcclusionStateNotification object:window];
+        [center removeObserver:self name:NSWindowWillStartLiveResizeNotification object:window];
+        [center removeObserver:self name:NSWindowDidEndLiveResizeNotification object:window];
         [center removeObserver:self name:NSWindowWillMoveNotification object:window];
         [center removeObserver:self name:NSWindowDidMoveNotification object:window];
         [center removeObserver:self name:NSWindowDidResizeNotification object:window];
@@ -870,7 +876,6 @@ static NSCursor *Cocoa_GetDesiredCursor(void)
         [center removeObserver:self name:NSWindowDidExitFullScreenNotification object:window];
         [center removeObserver:self name:@"NSWindowDidFailToEnterFullScreenNotification" object:window];
         [center removeObserver:self name:@"NSWindowDidFailToExitFullScreenNotification" object:window];
-        [center removeObserver:self name:NSWindowDidChangeOcclusionStateNotification object:window];
     } else {
         [window setDelegate:nil];
     }
@@ -997,6 +1002,26 @@ static NSCursor *Cocoa_GetDesiredCursor(void)
     }
 }
 
+- (void)windowWillStartLiveResize:(NSNotification *)aNotification
+{
+    // We'll try to maintain 60 FPS during live resizing
+    const NSTimeInterval interval = 1.0 / 60.0;
+    liveResizeTimer = [NSTimer scheduledTimerWithTimeInterval:interval
+                                                      repeats:TRUE
+                                                        block:^(NSTimer *unusedTimer)
+    {
+        SDL_OnWindowLiveResizeUpdate(_data.window);
+    }];
+
+    [[NSRunLoop currentRunLoop] addTimer:liveResizeTimer forMode:NSRunLoopCommonModes];
+}
+
+- (void)windowDidEndLiveResize:(NSNotification *)aNotification
+{
+    [liveResizeTimer invalidate];
+    liveResizeTimer = nil;
+}
+
 - (void)windowWillMove:(NSNotification *)aNotification
 {
     if ([_data.nswindow isKindOfClass:[SDL3Window class]]) {

src/video/windows/SDL_windowsevents.c

@@ -1541,12 +1541,7 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
     case WM_TIMER:
     {
         if (wParam == (UINT_PTR)SDL_IterateMainCallbacks) {
-            if (SDL_HasMainCallbacks()) {
-                SDL_IterateMainCallbacks(false);
-            } else {
-                // Send an expose event so the application can redraw
-                SDL_SendWindowEvent(data->window, SDL_EVENT_WINDOW_EXPOSED, 0, 0);
-            }
+            SDL_OnWindowLiveResizeUpdate(data->window);
             return 0;
         }
     } break;