Make classes not depend on the implicit GImGui context (#6199, #5856, #6199): ImGuiIO

This commit is a preparation toward adding ImGui apis with explicit context
and making ImGui applications being able to use multiple context at the same time
whatever their concurrency model.

About ImGuiIO:
- ImGuiIO depends on ImGuiContext because some of its method want to event to `g.InputEventQueue`.
- To make ImGuiIO aware of the context to use, context which creates the ImGuiIO is given as argument of ImGuiIO constructor.
- The assert `IM_ASSERT(&g.IO == this && "Can only add events to current context.")` has been removed since it does not make sense anymore

NOTE: ImGuiIO could be completely independent of ImGuiContext if the InputEventQueue was moved from ImGuiContext to ImGuiIO, but since
ImGuiIO is a public class it would expose InputEvent type. Solving this problem is out of the current scope, but it is interesting to notice.

docs/CHANGELOG.txt

@@ -54,6 +54,7 @@ Other changes:
 - Nav: Fixed an issue with Gamepad navigation when the movement lead to a scroll and
   frame time > repeat rate. Triggering a new move request on the same frame as a move
   result lead to an incorrect calculation and loss of navigation id. (#6171)
+- IO: Lifted constraint to call io.AddEventXXX functions from current context. (#4921, #5856, #6199)
 - Drag and Drop: Fixed handling of overlapping targets when smaller one is submitted
   before and can accept the same data type. (#6183).
 - Drag and Drop: Clear drag and drop state as soon as delivery is accepted in order to

imgui.cpp

@@ -1244,8 +1244,8 @@ ImGuiIO::ImGuiIO()
 // FIXME: Should in theory be called "AddCharacterEvent()" to be consistent with new API
 void ImGuiIO::AddInputCharacter(unsigned int c)
 {
-    ImGuiContext& g = *GImGui;
-    IM_ASSERT(&g.IO == this && "Can only add events to current context.");
+    IM_ASSERT(Ctx != NULL);
+    ImGuiContext& g = *Ctx;
     if (c == 0 || !AppAcceptingEvents)
         return;
 
@@ -1357,10 +1357,10 @@ static ImGuiInputEvent* FindLatestInputEvent(ImGuiInputEventType type, int arg =
 void ImGuiIO::AddKeyAnalogEvent(ImGuiKey key, bool down, float analog_value)
 {
     //if (e->Down) { IMGUI_DEBUG_LOG_IO("AddKeyEvent() Key='%s' %d, NativeKeycode = %d, NativeScancode = %d\n", ImGui::GetKeyName(e->Key), e->Down, e->NativeKeycode, e->NativeScancode); }
+    IM_ASSERT(Ctx != NULL);
     if (key == ImGuiKey_None || !AppAcceptingEvents)
         return;
-    ImGuiContext& g = *GImGui;
-    IM_ASSERT(&g.IO == this && "Can only add events to current context.");
+    ImGuiContext& g = *Ctx;
     IM_ASSERT(ImGui::IsNamedKeyOrModKey(key)); // Backend needs to pass a valid ImGuiKey_ constant. 0..511 values are legacy native key codes which are not accepted by this API.
     IM_ASSERT(!ImGui::IsAliasKey(key)); // Backend cannot submit ImGuiKey_MouseXXX values they are automatically inferred from AddMouseXXX() events.
     IM_ASSERT(key != ImGuiMod_Shortcut); // We could easily support the translation here but it seems saner to not accept it (TestEngine perform a translation itself)
@@ -1435,8 +1435,8 @@ void ImGuiIO::SetAppAcceptingEvents(bool accepting_events)
 // Queue a mouse move event
 void ImGuiIO::AddMousePosEvent(float x, float y)
 {
-    ImGuiContext& g = *GImGui;
-    IM_ASSERT(&g.IO == this && "Can only add events to current context.");
+    IM_ASSERT(Ctx != NULL);
+    ImGuiContext& g = *Ctx;
     if (!AppAcceptingEvents)
         return;
 
@@ -1459,8 +1459,8 @@ void ImGuiIO::AddMousePosEvent(float x, float y)
 
 void ImGuiIO::AddMouseButtonEvent(int mouse_button, bool down)
 {
-    ImGuiContext& g = *GImGui;
-    IM_ASSERT(&g.IO == this && "Can only add events to current context.");
+    IM_ASSERT(Ctx != NULL);
+    ImGuiContext& g = *Ctx;
     IM_ASSERT(mouse_button >= 0 && mouse_button < ImGuiMouseButton_COUNT);
     if (!AppAcceptingEvents)
         return;
@@ -1482,8 +1482,8 @@ void ImGuiIO::AddMouseButtonEvent(int mouse_button, bool down)
 // Queue a mouse wheel event (some mouse/API may only have a Y component)
 void ImGuiIO::AddMouseWheelEvent(float wheel_x, float wheel_y)
 {
-    ImGuiContext& g = *GImGui;
-    IM_ASSERT(&g.IO == this && "Can only add events to current context.");
+    IM_ASSERT(Ctx != NULL);
+    ImGuiContext& g = *Ctx;
 
     // Filter duplicate (unlike most events, wheel values are relative and easy to filter)
     if (!AppAcceptingEvents || (wheel_x == 0.0f && wheel_y == 0.0f))
@@ -1499,8 +1499,8 @@ void ImGuiIO::AddMouseWheelEvent(float wheel_x, float wheel_y)
 
 void ImGuiIO::AddFocusEvent(bool focused)
 {
-    ImGuiContext& g = *GImGui;
-    IM_ASSERT(&g.IO == this && "Can only add events to current context.");
+    IM_ASSERT(Ctx != NULL);
+    ImGuiContext& g = *Ctx;
 
     // Filter duplicate
     const ImGuiInputEvent* latest_event = FindLatestInputEvent(ImGuiInputEventType_Focus);

imgui.h

@@ -2022,6 +2022,8 @@ struct ImGuiIO
     // [Internal] Dear ImGui will maintain those fields. Forward compatibility not guaranteed!
     //------------------------------------------------------------------
 
+    ImGuiContext* Ctx;                              // Parent UI context (needs to be set explicitly by parent).
+
     // Main Input State
     // (this block used to be written by backend, since 1.87 it is best to NOT write to those directly, call the AddXXX functions above instead)
     // (reading from those variables is fair game, as they are extremely unlikely to be moving anywhere)

imgui_internal.h

@@ -1052,7 +1052,7 @@ struct IMGUI_API ImGuiMenuColumns
 // For a given item ID, access with ImGui::GetInputTextState()
 struct IMGUI_API ImGuiInputTextState
 {
-    ImGuiContext*           Ctx;                    // parent dear imgui context
+    ImGuiContext*           Ctx;                    // parent UI context (needs to be set explicitly by parent).
     ImGuiID                 ID;                     // widget id owning the text state
     int                     CurLenW, CurLenA;       // we need to maintain our buffer length in both UTF-8 and wchar format. UTF-8 length is valid even if TextA is not.
     ImVector<ImWchar>       TextW;                  // edit buffer, we need to persist but can't guarantee the persistence of the user-provided buffer. so we copy into own buffer.
@@ -1068,7 +1068,7 @@ struct IMGUI_API ImGuiInputTextState
     bool                    Edited;                 // edited this frame
     ImGuiInputTextFlags     Flags;                  // copy of InputText() flags. may be used to check if e.g. ImGuiInputTextFlags_Password is set.
 
-    ImGuiInputTextState(ImGuiContext* ctx)  { memset(this, 0, sizeof(*this)); Ctx = ctx;}
+    ImGuiInputTextState()                   { memset(this, 0, sizeof(*this)); }
     void        ClearText()                 { CurLenW = CurLenA = 0; TextW[0] = 0; TextA[0] = 0; CursorClamp(); }
     void        ClearFreeMemory()           { TextW.clear(); TextA.clear(); InitialTextA.clear(); }
     int         GetUndoAvailCount() const   { return Stb.undostate.undo_point; }
@@ -2013,8 +2013,10 @@ struct ImGuiContext
     ImVector<char>          TempBuffer;                         // Temporary text buffer
 
     ImGuiContext(ImFontAtlas* shared_font_atlas)
-        : InputTextState(this)
     {
+        IO.Ctx = this;
+        InputTextState.Ctx = this;
+
         Initialized = false;
         FontAtlasOwnedByContext = shared_font_atlas ? false : true;
         Font = NULL;