graphics: add option to disable win11 rounded corners on windows (#641)

## Description of change
This adds a toggleable option to remove the rounded window corners when
running a game, or a subscreen, in a window on Windows 11 and upwards.

## Testing
On Windows 11: Resort Anthem, MÚSECA and EPOLIS were tested and the
window corners were removed from both main windows and the TDJ subscreen
when running in windowed mode, with no change in fullscreen mode.

On Windows 7: IIDX18 was tested with no change, the call to
`DwmSetWindowAttribute` is ignored as `DWMWA_WINDOW_CORNER_PREFERENCE`
doesn't exist.

For XP builds, the call is compiled out to avoid linking against dwmapi
and windows_dll_compat_checker returns successfully when testing against
the XP Embedded image. I can't test it on XP, but it ran on Vista.

src/spice2x/hooks/graphics/graphics_windowed.cpp

@@ -24,6 +24,7 @@ std::optional<std::pair<uint32_t, uint32_t>> GRAPHICS_WINDOW_SIZE;
 std::optional<std::string> GRAPHICS_WINDOW_POS;
 bool GRAPHICS_WINDOW_ALWAYS_ON_TOP = false;
 bool GRAPHICS_WINDOW_BACKBUFFER_SCALE = false;
+bool GRAPHICS_WINDOW_DISABLE_ROUNDED_CORNERS = false;
 std::optional<HWND> GRAPHICS_HOOKED_WINDOW;
 
 // IIDX Windowed Subscreen - starts out as false, enabled by IIDX module on pre-attach as needed
@@ -132,6 +133,10 @@ void graphics_capture_initial_window(HWND hWnd) {
         log_info("graphics-windowed", "[{}] change window z-order - always on top", fmt::ptr(hWnd));
         graphics_update_z_order(hWnd, true);
     }
+    if (cfg::SCREENRESIZE->window_disable_round_corners) {
+        log_info("graphics-windowed", "[{}] disabling rounded corners", fmt::ptr(hWnd));
+        graphics_set_corner_preference(hWnd, true);
+    }
 
     // ensure spicetouch coordinates are initialized
     update_spicetouch_window_dimensions(hWnd);
@@ -181,6 +186,10 @@ void graphics_load_windowed_parameters() {
         cfg::SCREENRESIZE->window_always_on_top = true;
     }
 
+    if (GRAPHICS_WINDOW_DISABLE_ROUNDED_CORNERS) {
+        cfg::SCREENRESIZE->window_disable_round_corners = true;
+    }
+
     log_debug("graphics-windowed", "graphics_load_windowed_parameters returned");
 }
 
@@ -469,6 +478,27 @@ void graphics_update_z_order(HWND hWnd, bool always_on_top) {
     log_debug("graphics-windowed", "graphics_update_z_order returned");
 }
 
+void graphics_set_corner_preference(HWND hWnd, bool disable) {
+    if (!GRAPHICS_WINDOWED) {
+        return;
+    }
+
+#if !SPICE_XP
+    log_debug("graphics-windowed", "graphics_set_corner_preference called");
+
+    DWM_WINDOW_CORNER_PREFERENCE corner_preference = disable ? DWMWCP_DONOTROUND : DWMWCP_DEFAULT;
+    DwmSetWindowAttribute(
+        hWnd,
+        DWMWA_WINDOW_CORNER_PREFERENCE,
+        &corner_preference, sizeof(corner_preference));
+    
+    log_debug("graphics-windowed", "graphics_set_corner_preference returned");
+#else
+    // don't link against DwmSetWindowAttribute on XP
+    log_debug("graphics-windowed", "graphics_set_corner_preference called; ignoring");
+#endif
+}
+
 void graphics_move_resize_window(HWND hWnd) {
     if (!GRAPHICS_WINDOWED) {
         return;