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Gameplay Programming

Gameplay programming is the code that turns a game engine into a playable game: character movement, AI decisions, menus reacting to input, and the rules that decide what happens when things collide.

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Gameplay Programming

Gameplay programming is the code layer between a game engine's reusable systems and the specific rules of one game: what happens when the player presses jump, when a sword hits an enemy, when a quest condition becomes true. The engine supplies rendering, physics, and asset loading. Gameplay programming decides what the game actually does with them, frame by frame.

The game loop and timing

Every real-time game runs a loop that processes input, advances game state, and renders a frame, then repeats. The central design question is how time enters that loop. A variable timestep advances game state by however long the last frame took to render. This is simple, but it makes simulation results depend on frame rate: a physics calculation run in smaller steps on a fast machine accumulates different rounding error than the same calculation run in fewer, larger steps on a slow machine, so the two machines can diverge.

The fixed-timestep pattern fixes this by decoupling simulation from rendering. The loop tracks how much real time has elapsed since the last update in an accumulator variable, often called lag. While that accumulator holds at least one fixed step's worth of time, the loop calls update() and subtracts the step from the accumulator; only after the accumulator runs dry does the loop render a frame, using the leftover fraction of a step to interpolate positions smoothly between the last two simulated states. Gameplay logic and physics run at a constant, predictable rate regardless of how fast the machine renders, which is what makes fixed timestep the standard choice for physics-driven and networked games.

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