Method BeginDragDropSource

KBotExt/imgui/imgui.cpp:12320–12429

When this returns true you need to: a) call SetDragDropPayload() exactly once, b) you may render the payload visual/description, c) call EndDragDropSource() If the item has an identifier: - This assume/require the item to be activated (typically via ButtonBehavior). - Therefore if you want to use this with a mouse button other than left mouse button, it is up to the item itself to activate with an

// If the item has no identifier:
// - Currently always assume left mouse button.
bool ImGui::BeginDragDropSource(ImGuiDragDropFlags flags)
{
	ImGuiContext& g = *GImGui;
	ImGuiWindow* window = g.CurrentWindow;

	// FIXME-DRAGDROP: While in the common-most "drag from non-zero active id" case we can tell the mouse button,
	// in both SourceExtern and id==0 cases we may requires something else (explicit flags or some heuristic).
	ImGuiMouseButton mouse_button = ImGuiMouseButton_Left;

	bool source_drag_active = false;
	ImGuiID source_id = 0;
	ImGuiID source_parent_id = 0;
	if (!(flags & ImGuiDragDropFlags_SourceExtern))
	{
		source_id = g.LastItemData.ID;
		if (source_id != 0)
		{
			// Common path: items with ID
			if (g.ActiveId != source_id)
				return false;
			if (g.ActiveIdMouseButton != -1)
				mouse_button = g.ActiveIdMouseButton;
			if (g.IO.MouseDown[mouse_button] == false || window->SkipItems)
				return false;
			g.ActiveIdAllowOverlap = false;
		}
		else
		{
			// Uncommon path: items without ID
			if (g.IO.MouseDown[mouse_button] == false || window->SkipItems)
				return false;
			if ((g.LastItemData.StatusFlags & ImGuiItemStatusFlags_HoveredRect) == 0 && (g.ActiveId == 0 || g.ActiveIdWindow != window))
				return false;

			// If you want to use BeginDragDropSource() on an item with no unique identifier for interaction, such as Text() or Image(), you need to:
			// A) Read the explanation below, B) Use the ImGuiDragDropFlags_SourceAllowNullID flag.
			if (!(flags & ImGuiDragDropFlags_SourceAllowNullID))
			{
				IM_ASSERT(0);
				return false;
			}

			// Magic fallback to handle items with no assigned ID, e.g. Text(), Image()
			// We build a throwaway ID based on current ID stack + relative AABB of items in window.
			// THE IDENTIFIER WON'T SURVIVE ANY REPOSITIONING/RESIZINGG OF THE WIDGET, so if your widget moves your dragging operation will be canceled.
			// We don't need to maintain/call ClearActiveID() as releasing the button will early out this function and trigger !ActiveIdIsAlive.
			// Rely on keeping other window->LastItemXXX fields intact.
			source_id = g.LastItemData.ID = window->GetIDFromRectangle(g.LastItemData.Rect);
			KeepAliveID(source_id);
			bool is_hovered = ItemHoverable(g.LastItemData.Rect, source_id, g.LastItemData.InFlags);
			if (is_hovered && g.IO.MouseClicked[mouse_button])
			{
				SetActiveID(source_id, window);
				FocusWindow(window);
			}
			if (g.ActiveId == source_id) // Allow the underlying widget to display/return hovered during the mouse release frame, else we would get a flicker.
				g.ActiveIdAllowOverlap = is_hovered;
		}