Add VS Code dark non-client frame mod (#4464)

Adds a new mod: VS Code Dark Non-client Frame.

This mod forces Visual Studio Code’s Windows non-client frame into immersive dark mode. It fixes a visible 2px white bottom edge that can appear when VS Code is maximized with the custom title bar in Windows light mode, especially with a hidden or transparent taskbar.

## Changelog

If this pull request updates an existing mod, describe the changes below:

* N/A - this pull request introduces a new mod.

## Mod authorship

If this pull request introduces a new mod, please complete the section below.

This mod was created by:

- - [ ] The submitter, without AI assistance
- - [x] The submitter, with AI assistance
- - [ ] Claude
- - [x] ChatGPT
- - [ ] Gemini
- - [ ] Another AI (please specify): 
- - [ ] Other (please specify): 

Please select the options that best apply. Your selection does not affect the acceptance criteria, but it helps reviewers understand the context of the code and provide relevant feedback.

Author: v1b3s0

mods/vscode-dark-nonclient-frame.wh.cpp

@@ -0,0 +1,134 @@
+// ==WindhawkMod==
+// @id              vscode-dark-nonclient-frame
+// @name            VS Code Dark Non-client Frame
+// @description     Forces VS Code's non-client frame into dark mode to remove the light 2px bottom edge in Windows light mode.
+// @version         1.0
+// @author          v1b3s0
+// @github          https://github.com/v1b3s0
+// @license         MIT
+// @include         Code.exe
+// @compilerOptions -ldwmapi -luser32
+// ==/WindhawkMod==
+
+// ==WindhawkModReadme==
+/*
+# VS Code Dark Non-client Frame
+
+Forces Visual Studio Code's Windows non-client frame into immersive dark mode.
+
+This fixes the 2px light gray bottom edge that can appear when VS Code is maximized with the custom title bar in Windows light mode, especially with a hidden or transparent taskbar.
+
+Before:
+
+![Before](https://i.imgur.com/DVrOPag.png)
+
+After:
+
+![After](https://i.imgur.com/ldT3xJt.png)
+
+The mod targets only `Code.exe` by default. Users of VS Code Insiders, VSCodium, or renamed/portable builds can add the relevant executable name to the mod's custom include list.
+
+When the mod is disabled, it stops overriding VS Code's frame mode. Already affected windows may keep their current frame mode until VS Code applies a new value, for example after a theme or window state change.
+*/
+// ==/WindhawkModReadme==
+
+#include <dwmapi.h>
+#include <windhawk_api.h>
+
+using DwmSetWindowAttribute_t = decltype(&DwmSetWindowAttribute);
+DwmSetWindowAttribute_t DwmSetWindowAttribute_orig;
+
+BOOL IsCurrentProcessWindow(HWND hWnd) {
+    DWORD windowPid = 0;
+    GetWindowThreadProcessId(hWnd, &windowPid);
+
+    return windowPid == GetCurrentProcessId();
+}
+
+BOOL IsValidWindow(HWND hWnd) {
+    LONG_PTR style = GetWindowLongPtr(hWnd, GWL_STYLE);
+
+    return (style & WS_THICKFRAME) == WS_THICKFRAME ||
+           (style & WS_CAPTION) == WS_CAPTION;
+}
+
+void ApplyDarkFrame(HWND hWnd) {
+    if (!IsValidWindow(hWnd)) {
+        return;
+    }
+
+    BOOL enabled = TRUE;
+
+    DwmSetWindowAttribute_orig(
+        hWnd,
+        DWMWA_USE_IMMERSIVE_DARK_MODE,
+        &enabled,
+        sizeof(enabled)
+    );
+}
+
+HRESULT WINAPI DwmSetWindowAttribute_hook(
+    HWND hWnd,
+    DWORD dwAttribute,
+    LPCVOID pvAttribute,
+    DWORD cbAttribute
+) {
+    if (dwAttribute == DWMWA_USE_IMMERSIVE_DARK_MODE &&
+        IsCurrentProcessWindow(hWnd) &&
+        IsValidWindow(hWnd)) {
+        BOOL enabled = TRUE;
+
+        return DwmSetWindowAttribute_orig(
+            hWnd,
+            dwAttribute,
+            &enabled,
+            sizeof(enabled)
+        );
+    }
+
+    return DwmSetWindowAttribute_orig(
+        hWnd,
+        dwAttribute,
+        pvAttribute,
+        cbAttribute
+    );
+}
+
+BOOL CALLBACK EnableEnumWindowsCallback(HWND hWnd, LPARAM lParam) {
+    DWORD targetPid = static_cast<DWORD>(lParam);
+
+    DWORD windowPid = 0;
+    GetWindowThreadProcessId(hWnd, &windowPid);
+
+    if (targetPid == windowPid) {
+        ApplyDarkFrame(hWnd);
+    }
+
+    return TRUE;
+}
+
+BOOL Wh_ModInit() {
+    Wh_Log(L"Init");
+
+    Wh_SetFunctionHook(
+        (void*)DwmSetWindowAttribute,
+        (void*)DwmSetWindowAttribute_hook,
+        (void**)&DwmSetWindowAttribute_orig
+    );
+
+    return TRUE;
+}
+
+void Wh_ModAfterInit() {
+    Wh_Log(L"AfterInit");
+
+    EnumWindows(EnableEnumWindowsCallback, GetCurrentProcessId());
+}
+
+void Wh_ModBeforeUninit() {
+    Wh_Log(L"BeforeUninit");
+
+    // Do not force DWMWA_USE_IMMERSIVE_DARK_MODE to FALSE here.
+    // Disabling the mod should stop overriding VS Code's own value instead of
+    // forcing a light non-client frame.
+}