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Fix Your Timestep source @net8floz 2018

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What is it?

This is a series of scripts to help you unlock your framerate by implementing the ideas and solutions as presented by Glenn Fiedler at http://gafferongames.com/game-physics/fix-your-timestep/ to provide you with a fixed time step.

How to use?

First create an instance of FixedTimestep. Register objects or specific instances using the _register functions. You may register the id or object_index with either a user_event or script_index which will be executed during the fixed tick in the context of that instance.

The fixed step fires in the end step by default. You may prevent this by calling fixed_timestep_disable() and instead calling fixed_timestep_update() to update the tick manually.

Further Reading

Don't gather input (gamepad, keyboard, etc ) in your fixed timestep scripts or events. It should instead be used for physics calculations. The fixed timestep will be called 0-n amount of times per step based on the delta beween the current frame and the previous frame to attempt to skip or execute the tick to match the targeted frame rate and fps_real.

Typically you'll still use regular old time/dt based operation for a lot of things, like UI tweening, outside of the fixed timestep.

Example of render interpolation discussed on Gaffer On Games.

draw_sprite_ext(
	sprite_index,image_index,
	lerp(xprevious,x,global._ts_render_alpha),
	lerp(yprevious,y,global._ts_render_alpha),
	image_xscale,image_yscale,
	image_angle,image_blend,
	image_alpha
);

GM Pitfalls

GM wasn't intended to work this way. It has a lot of blackbox features that happen at specific points in it's own tick. You may now need to take care with certain things like the animation end event and watch for any other oddities that happen with other GM events.

Function reference

fixed_timestep_register_script(object_index | instance_id, script_index)

Registers an object_index or instance_id with the fixed timestep. The passed script will be executed in the scope of the registered instance on fixed tick.

fixed_timestep_register_user_event(object_index | instance_id, user_event_id)

Registers an object_index or instance_id with the fixed timestep. The passed user_event id will be executed using event_user(user_even_id) in the scope of the registered instance on fixed tick.

fixed_timestep_register_user_event(object_index | instance_id, user_event_id)

Registers an object_index or instance_id with the fixed timestep. The passed user_event id will be executed using event_user(user_even_id) in the scope of the registered instance on fixed tick.

fixed_timestep_unregister(object_index | instance_id)

Unregister an object_index or instance_id from the fixed timestep. This goes for both registered scripts and user event types.

fixed_timestep_set_disabled(boolean)

Prevents the fixed timestep from updated. By default the fixed timestep updates itself in it's step end event. To take control of the execution order disable the fixed timestep and update it yourself

fixed_timestep_update()

Updates the fixed timestep. This is called automatically in the FixTimestep object in the step end event. Only call this function if you have already disabled the fixed timestep.

fixed_timestep_set_target_fps

Sets the target fps for the fixed timestep. Is initially 60.

Credits