From 5235535cc2d3e251ed40d8df626c0b1275806877 Mon Sep 17 00:00:00 2001
From: frank <mailbox@shampoo.ooo>
Date: Tue, 5 Dec 2023 15:28:36 -0500
Subject: [PATCH] set window fullscreen display mode to current desktop mode
 before going fullscreen

---
 src/Display.cpp | 26 ++++++++++++++++++++++++--
 src/Display.hpp |  9 +++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/src/Display.cpp b/src/Display.cpp
index e921273..69f9269 100644
--- a/src/Display.cpp
+++ b/src/Display.cpp
@@ -184,8 +184,6 @@ void sb::Display::respond(SDL_Event& event)
     }
 }
 
-/* Use SDL window flags to determine if fullscreen is on or off and use SDL fullscreen
- * function to toggle the fullscreen state */
 void sb::Display::toggle_fullscreen() const
 {
     if (SDL_GetWindowFlags(const_cast<SDL_Window*>(window())) & SDL_WINDOW_FULLSCREEN)
@@ -195,6 +193,30 @@ void sb::Display::toggle_fullscreen() const
     }
     else
     {
+        /* Get the index of the display currently displaying the game window */
+        int display_index;
+        if ((display_index = SDL_GetWindowDisplayIndex(const_cast<SDL_Window*>(window()))) < 0)
+        {
+            display_index = 0;
+            sb::Log::sdl_error("Error getting current display index of window, defaulting to index 0.");
+        }
+
+        /* Get the display mode (including the resolution) of the display currently displaying the window */
+        SDL_DisplayMode mode;
+        if (SDL_GetDesktopDisplayMode(display_index, &mode) != 0)
+        {
+            sb::Log::sdl_error("Error getting display mode");
+        }
+        else
+        {
+            /* Set the window's fullscreen display mode to the same as the desktop to use the same resolution */
+            sb::Log::log("Setting window's fullscreen display mode to current desktop display mode");
+            if (SDL_SetWindowDisplayMode(const_cast<SDL_Window*>(window()), &mode) != 0)
+            {
+                sb::Log::sdl_error("Error setting window's fullscreen display mode");
+            }
+        }
+
         sb::Log::log("fullscreen requested");
         SDL_SetWindowFullscreen(const_cast<SDL_Window*>(window()), SDL_WINDOW_FULLSCREEN);
     }
diff --git a/src/Display.hpp b/src/Display.hpp
index 1991259..1b8e7f9 100644
--- a/src/Display.hpp
+++ b/src/Display.hpp
@@ -51,6 +51,15 @@ namespace sb
          */
         void respond(SDL_Event& event);
 
+        /*!
+         * Query SDL window flags to determine if fullscreen is on or off and use SDL's fullscreen function to toggle the fullscreen
+         * state to the opposite state.
+         *
+         * Before calling SDL's fullscreen function, this function queries the display index to find out which display (for example,
+         * which monitor in a dual-screen system) is displaying the window. It then sets the window's fullscreen display mode to the
+         * current desktop display mode of that display. This ensures that the fullscreen will succeed smoothly, without a resolution
+         * change, but it also requires that the game is adaptable to dynamic window sizing.
+         */
         void toggle_fullscreen() const;
 
     };