build: fizzy builds on dvui's SDL3 backend again, and CI keeps it

.github/workflows/ci.yml

@@ -159,6 +159,17 @@ jobs:
         shell: bash
         run: bash scripts/ci-retry.sh zig build check-web
 
+      # Fizzy on dvui's own SDL3 backend (`-Dnative-backend=sdl3`), where any dvui app on the stock
+      # backend stands: the platform pieces compile without fizzy's backend and lose what needs it
+      # (floats' windows, the window skin). It rotted unnoticed while nothing built it. macOS
+      # only: the platform reaches furthest into the backend there, and that is where it broke.
+      - name: Fetch dependencies for dvui's SDL3 backend (with retries)
+        if: matrix.name == 'macOS'
+        run: bash scripts/ci-retry.sh zig build --fetch -Dnative-backend=sdl3
+      - name: Compile on dvui's SDL3 backend
+        if: matrix.name == 'macOS'
+        run: bash scripts/ci-retry.sh zig build -Dnative-backend=sdl3 -Dno-emit --summary all
+
       # Fizzy consumed from outside: fizzyedit/example-app (fizzy as a library, in every shape)
       # and fizzyedit/example-plugin (the plugin template), built against this tree fetched as a
       # URL dependency would be. The only checks that catch a path resolving against the

backend/src/SDLBackend.zig

@@ -24,6 +24,10 @@ pub const Health = @import("Health.zig");
 /// What an app gets from its window beyond drawing into it: native dialogs, files the OS hands
 /// over, trackpad gestures, the window's chrome and state (`platform/`).
 pub const platform = @import("platform");
+// The platform knows this backend by that declaration (`platform.own_backend`).
+comptime {
+    std.debug.assert(platform.own_backend);
+}
 
 /// SDL3 only. Kept as a constant so the event code below stays a verbatim copy of dvui's
 /// `sdl.zig` (its `if (sdl3)` branches are the ones compiled).

backend/src/platform/macos/window_monitor.m

@@ -1206,11 +1206,14 @@ static void install_constrain_override(NSWindow *window) {
  * AppKit keeps the content rect across each change, so the window grew by its title bar and shrank
  * back: kept at will-enter it came back from full screen a title bar taller each time, and at
  * did-exit it jumped up a title bar and back down in a frame. A window the monitor follows keeps its
- * content under the title bar through any style it is given. */
+ * content under the title bar through any style it is given, and so does one that asked for that
+ * alone (`fizzy_macos_window_keep_full_size_content`). */
 static IMP g_nswindow_style_mask_imp = NULL;
+static char g_keeps_full_size_content;
 
 static void fizzy_set_style_mask(id self, SEL _cmd, NSWindowStyleMask mask) {
-    if (monitor_of((__bridge void *)self)) mask |= NSWindowStyleMaskFullSizeContentView;
+    if (monitor_of((__bridge void *)self) || objc_getAssociatedObject(self, &g_keeps_full_size_content))
+        mask |= NSWindowStyleMaskFullSizeContentView;
     ((void (*)(id, SEL, NSWindowStyleMask))g_nswindow_style_mask_imp)(self, _cmd, mask);
 }
 
@@ -1231,6 +1234,16 @@ static void install_style_mask_override(NSWindow *window) {
     }
 }
 
+/* `nswindow` keeps its content under the title bar through every style SDL gives it, as a followed
+ * window does, without the rest of the monitor: on a backend whose frames the monitor cannot step
+ * (`macos_monitor.zig`'s `install`), the window's chrome is still fizzy's. */
+void fizzy_macos_window_keep_full_size_content(void *nswindow) {
+    if (!nswindow) return;
+    NSWindow *window = (__bridge NSWindow *)nswindow;
+    objc_setAssociatedObject(window, &g_keeps_full_size_content, @YES, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
+    install_style_mask_override(window);
+}
+
 /* Keep `token`, an observer `m` added, to remove when the window is forgotten. */
 static void keep_observer(WindowMonitor *m, id token) {
     if (!m || !token || m->observer_count >= (int)(sizeof(m->observers) / sizeof(m->observers[0]))) return;

backend/src/platform/macos_monitor.zig

@@ -18,6 +18,7 @@ const dvui = @import("dvui");
 const Backend = @import("backend");
 const c = Backend.c;
 const window_layout = @import("window_layout.zig");
+const own_backend = @import("root.zig").own_backend;
 
 const log = std.log.scoped(.macos_monitor);
 
@@ -45,6 +46,7 @@ extern fn fizzy_macos_window_set_frame(cocoa_window: ?*anyopaque, x: f64, y: f64
 extern fn fizzy_macos_copy_screen_frames(out: [*]f64, max: c_int) c_int;
 extern fn fizzy_macos_window_sync_content_views(cocoa_window: ?*anyopaque) void;
 extern fn fizzy_macos_window_install_resize_observer(cocoa_window: ?*anyopaque) void;
+extern fn fizzy_macos_window_keep_full_size_content(cocoa_window: ?*anyopaque) void;
 extern fn fizzy_macos_window_sdl_draws_live_resize(cocoa_window: ?*anyopaque) c_int;
 extern fn fizzy_macos_window_space_step(cocoa_window: ?*anyopaque) void;
 extern fn fizzy_macos_window_space_moving(cocoa_window: ?*anyopaque) c_int;
@@ -369,10 +371,18 @@ export fn fizzy_macos_origin_nudged(cap_x: f64, cap_y: f64, cur_x: f64, cur_y: f
 /// Follow `win` through Spaces, zooms and live resizes: from here on AppKit's live sizes reach SDL
 /// before each frame (`Backend.SDLBackend.begin_hook`) and through every animation. Call once the
 /// window's chrome is in place, before it is shown.
+///
+/// This package's backend only. The monitor takes full screen and zooms over from AppKit and draws
+/// their steps itself, which needs that backend's frame hooks; on dvui's its steps were drawn out of
+/// time with the window. There the window goes in and out as AppKit and SDL take it, every query
+/// here answers from AppKit's own state, and the window only keeps its content under the title bar
+/// through SDL's styles, for fizzy's chrome (`styleTitled`): without that it came back from each
+/// round trip a title bar shorter.
 pub fn install(win: *dvui.Window) void {
     if (comptime builtin.os.tag != .macos) return;
     const back = win.backend.impl;
     const cocoa = cocoaWindowOf(back.window) orelse return;
+    if (comptime !own_backend) return fizzy_macos_window_keep_full_size_content(cocoa);
     macos_monitor_window = back.window;
     back.begin_hook = macosAppPreBeginSync;
     back.present_hook = macosAppPresented;

backend/src/platform/root.zig

@@ -17,6 +17,12 @@ pub const macos_monitor = @import("macos_monitor.zig");
 pub const window_layout = @import("window_layout.zig");
 pub const menu = @import("menu.zig");
 
+/// Whether the app is on this package's backend (`SDLBackend`, which imports these pieces) rather
+/// than dvui's own SDL3 backend. What they reach into beyond SDL's window — floats' windows, the
+/// window skin, the present hook — is there only; on dvui's, those parts do nothing. One flag, not
+/// a `@hasField` per field: a field renamed on this backend then fails its build, not goes quiet.
+pub const own_backend = @hasDecl(@import("backend"), "platform");
+
 comptime {
     // The menu bar's Objective-C (`macos/menu_target.m`) calls these back, and it is compiled into
     // every app on macOS (`addPlatformObjC`), so they are kept whether or not the app ever reaches

backend/src/platform/window.zig

@@ -9,6 +9,7 @@ const objc = @import("objc");
 const titlebar = @import("titlebar.zig");
 const win32_titlebar = @import("win32_titlebar.zig");
 const linux_titlebar = @import("linux_titlebar.zig");
+const own_backend = @import("root.zig").own_backend;
 
 const NSPoint = extern struct { x: f64, y: f64 };
 const NSSize = extern struct { width: f64, height: f64 };
@@ -299,12 +300,12 @@ pub fn setStyle(win: *dvui.Window) void {
         // Not a menu's or a dialog's: dressed once as it opens (`fizzy_macos_viewport_menu`), it
         // never goes full screen, and this made it a full-screen primary window over the
         // auxiliary one it was opened as, every frame.
-        for (&win.backend.impl.viewport_slots) |*slot| {
+        if (comptime own_backend) for (&win.backend.impl.viewport_slots) |*slot| {
             const vp = if (slot.*) |*v| v else continue;
             if (vp.passive or vp.menu) continue;
             const ns = c.SDL_GetPointerProperty(c.SDL_GetWindowProperties(vp.window), c.SDL_PROP_WINDOW_COCOA_WINDOW_POINTER, null) orelse continue;
             styleTitled(ns);
-        }
+        };
     } else if (builtin.os.tag == .windows) {
         win32_titlebar.applyChrome(win);
     } else if (builtin.os.tag == .linux) {
@@ -422,12 +423,14 @@ pub fn setBackground(win: *dvui.Window, color: dvui.Color) void {
             skin(raw_ptr.?, color, dvui.themeGet().dark);
             // Every float's own window too, and each opened from now on (`SDLBackend.viewportGlass`):
             // side by side, and each in a Space of its own, they are one app's windows.
-            win.backend.impl.window_skin = color;
-            for (&win.backend.impl.viewport_slots) |*slot| {
-                const vp = if (slot.*) |*v| v else continue;
-                if (vp.passive) continue;
-                const ns = c.SDL_GetPointerProperty(c.SDL_GetWindowProperties(vp.window), c.SDL_PROP_WINDOW_COCOA_WINDOW_POINTER, null) orelse continue;
-                skin(ns, color, dvui.themeGet().dark);
+            if (comptime own_backend) {
+                win.backend.impl.window_skin = color;
+                for (&win.backend.impl.viewport_slots) |*slot| {
+                    const vp = if (slot.*) |*v| v else continue;
+                    if (vp.passive) continue;
+                    const ns = c.SDL_GetPointerProperty(c.SDL_GetWindowProperties(vp.window), c.SDL_PROP_WINDOW_COCOA_WINDOW_POINTER, null) orelse continue;
+                    skin(ns, color, dvui.themeGet().dark);
+                }
             }
 
             // SDL3 currently removes the shadow when the transparency flag for the window is set. This brings it back.