Backends, Examples: Add comments about using WndProc handler and WantCaptureXXX flags. (#5061)

+ update README.

backends/imgui_impl_allegro5.cpp

@@ -456,8 +456,8 @@ static void ImGui_ImplAllegro5_UpdateKeyModifiers()
 }
 
 // You can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if dear imgui wants to use your inputs.
-// - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application.
-// - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application.
+// - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application, or clear/overwrite your copy of the mouse data.
+// - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application, or clear/overwrite your copy of the keyboard data.
 // Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.
 bool ImGui_ImplAllegro5_ProcessEvent(ALLEGRO_EVENT* ev)
 {

backends/imgui_impl_sdl.cpp

@@ -237,8 +237,8 @@ static void ImGui_ImplSDL2_UpdateKeyModifiers(SDL_Keymod sdl_key_mods)
 }
 
 // You can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if dear imgui wants to use your inputs.
-// - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application.
-// - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application.
+// - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application, or clear/overwrite your copy of the mouse data.
+// - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application, or clear/overwrite your copy of the keyboard data.
 // Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.
 // If you have multiple SDL events and some of them are not meant to be used by dear imgui, you may need to filter events based on their windowID field.
 bool ImGui_ImplSDL2_ProcessEvent(const SDL_Event* event)

backends/imgui_impl_win32.cpp

@@ -488,10 +488,10 @@ static ImGuiKey ImGui_ImplWin32_VirtualKeyToImGuiKey(WPARAM wParam)
 #endif
 
 // Win32 message handler (process Win32 mouse/keyboard inputs, etc.)
-// Call from your application's message handler.
+// Call from your application's message handler. Keep calling your message handler unless this function returns TRUE.
 // When implementing your own backend, you can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if Dear ImGui wants to use your inputs.
-// - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application.
-// - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application.
+// - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application, or clear/overwrite your copy of the mouse data.
+// - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application, or clear/overwrite your copy of the keyboard data.
 // Generally you may always pass all inputs to Dear ImGui, and hide them from your application based on those two flags.
 // PS: In this Win32 handler, we use the capture API (GetCapture/SetCapture/ReleaseCapture) to be able to read mouse coordinates when dragging mouse outside of our window bounds.
 // PS: We treat DBLCLK messages as regular mouse down messages, so this code will work on windows classes that have the CS_DBLCLKS flag set. Our own example app code doesn't set this flag.

backends/imgui_impl_win32.h

@@ -22,6 +22,8 @@ IMGUI_IMPL_API void     ImGui_ImplWin32_NewFrame();
 // Win32 message handler your application need to call.
 // - Intentionally commented out in a '#if 0' block to avoid dragging dependencies on <windows.h> from this helper.
 // - You should COPY the line below into your .cpp code to forward declare the function and then you can call it.
+// - Call from your application's message handler. Keep calling your message handler unless this function returns TRUE.
+
 #if 0
 extern IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);
 #endif