Jerky to Smooth: Techniques for Achieving Fluid Movement in Networked Action Games.
In networked action games, smooth visuals and responsiveness to player input are crucial for an enjoyable experience. This talk, “Structure of Networked Action Games,” by Lila Games Principal Engineer Basudev Patel, explores how decoupling simulation and rendering helps achieve these qualities.
The foundation of a video game is the simulation loop, which takes the current game state and player input to produce a new state that is rendered to the screen. This process repeats frame after frame, driving the game forward. To ensure consistent gameplay across different computer speeds, game developers often scale calculations by the time elapsed (delta time).
However, using delta time can introduce issues, especially with physics simulations like projectile motion. Variations in delta time can lead to discrepancies in the projectile’s trajectory across different frame rates.
The solution is to use fixed time steps, similar to the fixed update in physics engines and tick-based systems in multiplayer games. This approach ensures that the game state is updated at a consistent rate, regardless of frame rate variations.
However, simulating gameplay at a fixed rate can lead to choppy visuals, especially on higher refresh rate displays. Decoupling the simulation and rendering allows for smoother visuals.
Here’s how it works:
- The game simulation runs at a fixed rate in the fixed update loop.
- The rendering loop runs independently at a higher rate, interpolating between the simulated game states to produce smoother visuals.
This technique can be applied to various aspects of gameplay, such as player movement and projectile motion. For example, in player movement, the rendered position of the player can be smoothly interpolated between the simulated positions. In projectile motion, the projectile’s position can be rendered ahead based on its simulated velocity.
To further enhance responsiveness, player input can be predicted ahead of the simulation. This means that the rendered position of the player is calculated based on the predicted input, even before the simulation has processed it. However, this can introduce errors, requiring techniques like error correction to adjust the rendered position towards the actual simulated position.
Decoupling simulation and rendering provides a powerful way to enhance the visual quality and responsiveness of video games. By understanding the underlying concepts and techniques, game developers can create more immersive and enjoyable gaming experiences.