Example text input with autocomplete popup

AutoComplete.cpp

#include <imgui_internal.h>

namespace ImGui
{
	inline void ResetTextInputState(ImGuiID anId)
	{
		// Requires imgui update
		//if (GImGui->InputTextState.ID == anId)
		//	GImGui->InputTextState.Reinitialize = true;

		if (GImGui->InputTextState.ID == anId)
			GImGui->InputTextState.Stb.cursor = 10000;
	}
}

bool ImAutoCompleteText::Update(char const* anId, GC_ArrayRange<GC_String> const& someAutoCompletes, ImGuiInputTextFlags aFlags)
{
	struct CallbackData
	{
		ImAutoCompleteText* Text;
		GC_ArrayRange<GC_String> const* AutoCompletes;
		uint AutoCompleteSelection;
	} data = { this, &someAutoCompletes, someAutoCompletes.Count() };

	if (mySelection >= someAutoCompletes.Count())
	{
		mySelection = 0;
	}

	ImVec2 startPos = ImGui::GetCursorPos();
	ImVec2 startScreenPos = ImGui::GetCursorScreenPos();

	bool result = ImGui::InputText(anId, myText.Buffer(), myText.Capacity(), ImGuiInputTextFlags_CallbackCompletion | ImGuiInputTextFlags_CallbackHistory | ImGuiInputTextFlags_EnterReturnsTrue | aFlags,
		[](ImGuiInputTextCallbackData* data) -> int
		{
			CallbackData* callbackData = (CallbackData*)data->UserData;
			if (data->EventFlag == ImGuiInputTextFlags_CallbackCompletion)
			{
				callbackData->AutoCompleteSelection = callbackData->Text->mySelection;
			}
			else if (data->EventFlag == ImGuiInputTextFlags_CallbackHistory)
			{
				if (data->EventKey == ImGuiKey_UpArrow)
				{
					if (callbackData->Text->mySelection > 0)
						--callbackData->Text->mySelection;
				}
				else if (callbackData->AutoCompletes->Count() && callbackData->Text->mySelection < callbackData->AutoCompletes->Count() - 1)
				{
					++callbackData->Text->mySelection;
				}
			}
			return 0;
		},
		&data);

	if (myResetFocus)
	{
		myResetFocus = false;
		ImGui::SetKeyboardFocusHere(-1);
	}

	ImGuiID id = ImGui::GetID(anId);

	if (data.AutoCompleteSelection != someAutoCompletes.Count())
	{
		myText = someAutoCompletes[data.AutoCompleteSelection];
		ImGui::ResetTextInputState(id);
	}

	if (!ImGui::IsItemEnabled() || someAutoCompletes.Count() == 0)
	{
		myIsPopupActive = false;
	}
	else if (ImGui::IsItemActive())
	{
		myIsPopupActive = true;
	}

	if (myIsPopupActive)
	{
		// Draw popup window
		ImGuiWindowFlags popupFlags =
			ImGuiWindowFlags_NoTitleBar |
			ImGuiWindowFlags_NoResize |
			ImGuiWindowFlags_NoMove |
			ImGuiWindowFlags_HorizontalScrollbar |
			ImGuiWindowFlags_NoSavedSettings |
			ImGuiWindowFlags_NoDocking |
			ImGuiWindowFlags_AlwaysAutoResize;

		ImVec2 endPos = ImGui::GetCursorPos();
		GC_Vector2f winPos = ImGui::GetWindowPos();

		if (startPos.y - winPos.y > ImGui::GetContentRegionAvail().y)
		{
			// appear on top
			ImGui::SetNextWindowPos(startScreenPos, 0, { 0, 1 });
		}
		else
		{
			// appear on top
			ImGui::SetNextWindowPos(ImGui::GetCursorScreenPos());
		}

		ImGui::SetNextWindowSizeConstraints({ -1, 0 }, { -1, ImGui::GetTextLineHeight() * 16 });
		ImGui::Begin("history_popup", nullptr, popupFlags);
		ImGui::PushAllowKeyboardFocus(false);

		for_index(char const* ac : someAutoCompletes)
		{
			bool selected = i == mySelection;
			if (ImGui::Selectable(ac, &selected))
			{
				myText = ac;
				myResetFocus = true;
				ImGui::ResetTextInputState(id);
			}
		}

		ImGui::PopAllowKeyboardFocus();

		if (!ImGui::IsWindowFocused(ImGuiHoveredFlags_RootAndChildWindows))
			myIsPopupActive = false;

		ImGui::End();
	}

	return result;
}

AutoComplete.h

#pragma once

struct ImAutoCompleteText
{
	ImAutoCompleteText() : mySelection(0), myDrawBelow(false), myIsPopupActive(false) {}

	bool Update(char const* anId, GC_ArrayRange<GC_String> const& someAutoCompletes, ImGuiInputTextFlags aFlags = 0);

	GC_StaticString<1024> myText;
	uint mySelection;
	bool myDrawBelow;
	bool myIsPopupActive;
	bool myResetFocus;
};