Backends: SDL: Disable SDL 2.0.22 new "auto capture" which prevents drag and drop across windows, and don't capture mouse when drag and dropping. (ocornut#5710)

Author: ocornut

backends/imgui_impl_sdl.cpp

@@ -18,6 +18,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2022-09-26: Inputs: Disable SDL 2.0.22 new "auto capture" (SDL_HINT_MOUSE_AUTO_CAPTURE) which prevents drag and drop across windows for multi-viewport support + don't capture when drag and dropping. (#5710)
 //  2022-09-26: Inputs: Renamed ImGuiKey_ModXXX introduced in 1.87 to ImGuiMod_XXX (old names still supported).
 //  2022-03-22: Inputs: Fix mouse position issues when dragging outside of boundaries. SDL_CaptureMouse() erroneously still gives out LEAVE events when hovering OS decorations.
 //  2022-03-22: Inputs: Added support for extra mouse buttons (SDL_BUTTON_X1/SDL_BUTTON_X2).
@@ -76,7 +77,6 @@
 #else
 #define SDL_HAS_CAPTURE_AND_GLOBAL_MOUSE    0
 #endif
-#define SDL_HAS_MOUSE_FOCUS_CLICKTHROUGH    SDL_VERSION_ATLEAST(2,0,5)
 #define SDL_HAS_VULKAN                      SDL_VERSION_ATLEAST(2,0,6)
 
 // SDL Data
@@ -367,15 +367,20 @@ static bool ImGui_ImplSDL2_Init(SDL_Window* window, SDL_Renderer* renderer)
     (void)window;
 #endif
 
-    // Set SDL hint to receive mouse click events on window focus, otherwise SDL doesn't emit the event.
+    // From 2.0.5: Set SDL hint to receive mouse click events on window focus, otherwise SDL doesn't emit the event.
     // Without this, when clicking to gain focus, our widgets wouldn't activate even though they showed as hovered.
     // (This is unfortunately a global SDL setting, so enabling it might have a side-effect on your application.
     // It is unlikely to make a difference, but if your app absolutely needs to ignore the initial on-focus click:
     // you can ignore SDL_MOUSEBUTTONDOWN events coming right after a SDL_WINDOWEVENT_FOCUS_GAINED)
-#if SDL_HAS_MOUSE_FOCUS_CLICKTHROUGH
+#ifdef SDL_HINT_MOUSE_FOCUS_CLICKTHROUGH
     SDL_SetHint(SDL_HINT_MOUSE_FOCUS_CLICKTHROUGH, "1");
 #endif
 
+    // From 2.0.22: Disable auto-capture, this is preventing drag and drop across multiple windows (see #5710)
+#ifdef SDL_HINT_MOUSE_AUTO_CAPTURE
+    SDL_SetHint(SDL_HINT_MOUSE_AUTO_CAPTURE, "0");
+#endif
+
     return true;
 }
 
@@ -435,7 +440,7 @@ static void ImGui_ImplSDL2_UpdateMouseData()
     // We forward mouse input when hovered or captured (via SDL_MOUSEMOTION) or when focused (below)
 #if SDL_HAS_CAPTURE_AND_GLOBAL_MOUSE
     // SDL_CaptureMouse() let the OS know e.g. that our imgui drag outside the SDL window boundaries shouldn't e.g. trigger other operations outside
-    SDL_CaptureMouse(bd->MouseButtonsDown != 0 ? SDL_TRUE : SDL_FALSE);
+    SDL_CaptureMouse((bd->MouseButtonsDown != 0 && ImGui::GetDragDropPayload() == NULL) ? SDL_TRUE : SDL_FALSE);
     SDL_Window* focused_window = SDL_GetKeyboardFocus();
     const bool is_app_focused = (bd->Window == focused_window);
 #else

docs/CHANGELOG.txt

@@ -148,6 +148,8 @@ Other Changes:
 - Demo: Added more explicit "Center window" mode to "Overlay example". (#5618)
 - Examples: Added all SDL examples to default VS solution.
 - Backends: GLFW: Honor GLFW_CURSOR_DISABLED by not setting mouse position. (#5625) [@scorpion-26]
+- Backends: SDL: Disable SDL 2.0.22 new "auto capture" which prevents drag and drop across windows
+  (e.g. for multi-viewport support) and don't capture mouse when drag and dropping. (#5710)
 - Backends: Metal: Use __bridge for ARC based systems. (#5403) [@stack]
 - Backends: Metal: Add dispatch synchronization. (#5447) [@luigifcruz]
 - Backends: Metal: Update deprecated property 'sampleCount'->'rasterSampleCount'. (#5603) [@dcvz]