Backends: SDL2, SDL3: storing SDL_WindowID inside ImGuiViewport::PlatformHandle instead of SDL_Window*. (#7853)

This will be used to support filtering of events with multi-viewports.

backends/imgui_impl_sdl2.cpp

diff --git a/backends/imgui_impl_sdl2.cpp b/backends/imgui_impl_sdl2.cpp
index 9fff2ab..c472496 100644
--- a/backends/imgui_impl_sdl2.cpp
+++ b/backends/imgui_impl_sdl2.cpp
@@ -21,6 +21,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2024-08-19: Storing SDL's Uint32 WindowID inside ImGuiViewport::PlatformHandle instead of SDL_Window*.
 //  2024-08-19: ImGui_ImplSDL2_ProcessEvent() now ignores events intended for other SDL windows. (#7853)
 //  2024-07-02: Emscripten: Added io.PlatformOpenInShellFn() handler for Emscripten versions.
 //  2024-07-02: Update for io.SetPlatformImeDataFn() -> io.PlatformSetImeDataFn() renaming in main library.
@@ -483,7 +484,7 @@
     // Set platform dependent data in viewport
     // Our mouse update function expect PlatformHandle to be filled for the main viewport
     ImGuiViewport* main_viewport = ImGui::GetMainViewport();
-    main_viewport->PlatformHandle = (void*)window;
+    main_viewport->PlatformHandle = (void*)(intptr_t)bd->WindowID;
     main_viewport->PlatformHandleRaw = nullptr;
     SDL_SysWMinfo info;
     SDL_VERSION(&info.version);

backends/imgui_impl_sdl3.cpp

diff --git a/backends/imgui_impl_sdl3.cpp b/backends/imgui_impl_sdl3.cpp
index 5a58c96..2462734 100644
--- a/backends/imgui_impl_sdl3.cpp
+++ b/backends/imgui_impl_sdl3.cpp
@@ -21,6 +21,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2024-08-19: Storing SDL_WindowID inside ImGuiViewport::PlatformHandle instead of SDL_Window*.
 //  2024-08-19: ImGui_ImplSDL3_ProcessEvent() now ignores events intended for other SDL windows. (#7853)
 //  2024-07-22: Update for SDL3 api changes: SDL_GetGamepads() memory ownership change. (#7807)
 //  2024-07-18: Update for SDL3 api changes: SDL_GetClipboardText() memory ownership change. (#7801)
@@ -133,7 +134,8 @@
 static void ImGui_ImplSDL3_PlatformSetImeData(ImGuiContext*, ImGuiViewport* viewport, ImGuiPlatformImeData* data)
 {
     ImGui_ImplSDL3_Data* bd = ImGui_ImplSDL3_GetBackendData();
-    SDL_Window* window = (SDL_Window*)viewport->PlatformHandle;
+    SDL_WindowID window_id = (SDL_WindowID)(intptr_t)viewport->PlatformHandle;
+    SDL_Window* window = SDL_GetWindowFromID(window_id);
     if ((data->WantVisible == false || bd->ImeWindow != window) && bd->ImeWindow != NULL)
     {
         SDL_StopTextInput(bd->ImeWindow);
@@ -413,7 +415,7 @@
 
 static void ImGui_ImplSDL3_SetupPlatformHandles(ImGuiViewport* viewport, SDL_Window* window)
 {
-    viewport->PlatformHandle = window;
+    viewport->PlatformHandle = (void*)(intptr_t)SDL_GetWindowID(window);
     viewport->PlatformHandleRaw = nullptr;
 #if defined(_WIN32) && !defined(__WINRT__)
     viewport->PlatformHandleRaw = (HWND)SDL_GetPointerProperty(SDL_GetWindowProperties(window), SDL_PROP_WINDOW_WIN32_HWND_POINTER, nullptr);

docs/CHANGELOG.txt

diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index e272b19..24f6c64 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -51,6 +51,7 @@
 - Backends: GLFW: added ImGui_ImplGlfw_Sleep() helper function because GLFW does not
   provide a way to do a portable sleep. (#7844)
 - Backends: SDL2, SDL3: ignore events of other SDL windows. (#7853) [@madebr, @ocornut]
+- Backends: SDL2, SDL3: storing SDL_WindowID inside ImGuiViewport::PlatformHandle instead of SDL_Window*.
 - Examples: GLFW (all), SDL2 (all), SDL3 (all), Win32+OpenGL3: rework examples main loop
   to handle minimization without burning CPU or GPU by running unthrottled code. (#7844)