Fix SDL Gamepad handling

SDL_OpenGamepad(0) doesn't work with latest SDL3.
Now we need to get all the gamepags, then we need to open it:
    int pads = 0;
    auto ids = SDL_GetGamepads(&pads);
    auto joyId = SDL_OpenGamepad(ids[0]);
    ...
    SDL_CloseGamepad(joyId);

A new function ImGui_ImplSDL3_SetGamepad is needed to allow the user to
set which gamepad will be used for Ui Navigation, as we shouldn't open/
close the gamepad for each frame.

backends/imgui_impl_sdl3.cpp

@@ -71,6 +71,7 @@ struct ImGui_ImplSDL3_Data
  int PendingMouseLeaveFrame;
  char* ClipboardTextData;
  bool MouseCanUseGlobalState;
+ SDL_Gamepad* Gamepad;
 
  ImGui_ImplSDL3_Data() { memset((void*)this, 0, sizeof(*this)); }
 };
@@ -531,15 +532,15 @@ static void ImGui_ImplSDL3_UpdateGamepads()
 
  // Get gamepad
  io.BackendFlags &= ~ImGuiBackendFlags_HasGamepad;
- SDL_Gamepad* gamepad = SDL_OpenGamepad(0);
- if (!gamepad)
+ ImGui_ImplSDL3_Data* bd = ImGui_ImplSDL3_GetBackendData();
+ if (!bd->Gamepad)
  return;
  io.BackendFlags |= ImGuiBackendFlags_HasGamepad;
 
  // Update gamepad inputs
  #define IM_SATURATE(V) (V < 0.0f ? 0.0f : V > 1.0f ? 1.0f : V)
- #define MAP_BUTTON(KEY_NO, BUTTON_NO) { io.AddKeyEvent(KEY_NO, SDL_GetGamepadButton(gamepad, BUTTON_NO) != 0); }
- #define MAP_ANALOG(KEY_NO, AXIS_NO, V0, V1) { float vn = (float)(SDL_GetGamepadAxis(gamepad, AXIS_NO) - V0) / (float)(V1 - V0); vn = IM_SATURATE(vn); io.AddKeyAnalogEvent(KEY_NO, vn > 0.1f, vn); }
+ #define MAP_BUTTON(KEY_NO, BUTTON_NO) { io.AddKeyEvent(KEY_NO, SDL_GetGamepadButton(bd->Gamepad, BUTTON_NO) != 0); }
+ #define MAP_ANALOG(KEY_NO, AXIS_NO, V0, V1) { float vn = (float)(SDL_GetGamepadAxis(bd->Gamepad, AXIS_NO) - V0) / (float)(V1 - V0); vn = IM_SATURATE(vn); io.AddKeyAnalogEvent(KEY_NO, vn > 0.1f, vn); }
  const int thumb_dead_zone = 8000; // SDL_gamecontroller.h suggests using this value.
  MAP_BUTTON(ImGuiKey_GamepadStart, SDL_GAMEPAD_BUTTON_START);
  MAP_BUTTON(ImGuiKey_GamepadBack, SDL_GAMEPAD_BUTTON_BACK);
@@ -609,10 +610,18 @@ void ImGui_ImplSDL3_NewFrame()
  ImGui_ImplSDL3_UpdateGamepads();
 }
 
+
+void ImGui_ImplSDL3_SetGamepad(SDL_Gamepad *gamepad)
+{
+ ImGui_ImplSDL3_Data* bd = ImGui_ImplSDL3_GetBackendData();
+ bd->Gamepad = gamepad;
+}
+
 //-----------------------------------------------------------------------------
 
 #if defined(__clang__)
 #pragma clang diagnostic pop
 #endif
 
 #endif // #ifndef IMGUI_DISABLE
+

backends/imgui_impl_sdl3.h

@@ -26,6 +26,7 @@
 
 struct SDL_Window;
 struct SDL_Renderer;
+struct SDL_Gamepad;
 typedef union SDL_Event SDL_Event;
 
 IMGUI_IMPL_API bool ImGui_ImplSDL3_InitForOpenGL(SDL_Window* window, void* sdl_gl_context);
@@ -37,5 +38,5 @@ IMGUI_IMPL_API bool ImGui_ImplSDL3_InitForOther(SDL_Window* window);
 IMGUI_IMPL_API void ImGui_ImplSDL3_Shutdown();
 IMGUI_IMPL_API void ImGui_ImplSDL3_NewFrame();
 IMGUI_IMPL_API bool ImGui_ImplSDL3_ProcessEvent(const SDL_Event* event);
-
+IMGUI_IMPL_API void ImGui_ImplSDL3_SetGamepad(SDL_Gamepad* gamepad);
 #endif // #ifndef IMGUI_DISABLE