How Devs Give The Player Control in Half Life Alyx - Anim Interactables
146I've been enjoying playing through Alyx with the dev commentary. I found this fascinating because we get to see what goes on behind the scenes (BTS) on how the developers give us the players control of analog interfaces. The Valve team has stellar talent! BTS is some of my favorite things to watch!
My First VR Game Playthrough (HL: Alyx)
• Half Life: Alyx (First VR Game)
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DEVELOPER COMMENTARY:
In traditional games, analog controls like levers, dials, and crank wheels usually play simple animations in response to a player's mouse click or key press. In VR, however, players with tracked hand controllers expect to be able to control analog interfaces by grabbing and moving them directly. To support this, we developed a new system that we call Anim Interactables.
The opening mechanism of this health station is a good example of an Anim Interactable. To your left and right, you can see some more examples, such as a large railroad switch, the Vortigaunt's fire alarm doorbell, a crank wheel, a rolling cabinet door, and both the antenna and tuning dial on the radio. Anim Interactables like these allow us to give the player control of analog interfaces while constraining their input to an authored range of motion.
The system uses the position and orientation of the player's hand to drive the animation of a model which defines the analog interface. As the player moves their tracked controller, the Anim Interactable continuously performs a search to determine if playing the animation forward or backward will place the interaction point closer to the tracked controller's position in space. This allows the player to drag the animation forward, backward, or hold it stationary.
The result is an intuitive correspondence between the player's body and the virtual interface. Furthermore, these interactive animations don't necessarily have to make physical sense. Artists simply animate the range of motion they want the player to be able to control. These Anim Interactables have their debug visualizations turned on, so you can see the authored range of motion, including the non-linear paths used on the railroad switch, the health station, and the crank wheel.
Anim Interactables allowed us to make all kinds of objects in the world interactive, from mundane man-made devices to intricate Combine mechanisms, without the need to run complex physical simulations.
Feel free to play around with the Anim Interactables in this area before moving on.
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