The way in which the game communicates and interacts with the player is extremely important. User Interfaces (UIs) and Heads-up Displays (HUDs) are the games' way of providing information about the game to the player and in some cases allowing the player to interact with the game.
Unreal Engine 4 provides multiple means of creating UIs and HUDs. The
Canvas class can be used to draw directly to the screen at a low level, overlaid onto the world.
The game's Interface is used to convey information to the player and provide a means of prompting the user for directed input.
A game interface generally consists of two main elements: the heads-up display (HUD) and menus or user interfaces (UIs).
The HUD refers to the status and information overlaid on the screen during gameplay. The purpose of the HUD
is to inform the player of the current state of the game, i.e. the score, their health, the amount of time remaining,
etc. The HUD is usually non-interactive, meaning the player does not click on elements of the HUD, though this
becomes a gray area in certain types of games where the HUD and user interfaces are hard to separate.
User Interfaces refer to menus and other interactive elements. These elements are usually drawn overlaid on
the screen much like the HUD, but in certain circumstances they could be part of the game world itself rendered
onto a surface in the world. The most obvious examples of UIs are the main menu displayed when the game starts up
or the pause menu shown when the player has paused the game. However, other UIs may be displayed during play. These
could be used to show dialog between characters in the game or in more complex situations, such as in an RTS or RPG,
they may be integral to the game play itself allowing the player to choose weapons, armor, units to build, etc.