Force types

All custom forces extend the Force class, and are configured in a similar way. All forces are functions run in a GPU compute shader, they differ primarily in which parameters they have access to (ex. pairwise functions get the distance between a particle pair.)

Like the rest of the GPU code in this program, these are written with KSL, with examples available in the demo module.

Defining a force

Extend one of the force type classes (ex. PairwiseForce) and implement createFunction. These also take a name for your force, which will be used in configs. See also the pages for each force on the sidebar.

Below is a full example for an individual force shader, with explanations following it:

object ConstantForce : IndividualForce("gravity") {
    // define parameters here
    val force = param<Float>("force")
    
    override fun KslIndividualForceFunction.createFunction() {
        // convert to shader parameters here
        val force = force.asShaderParam()
        
        body {
            // KSL shader code here
            float3Value(0f.const, force, 0f.const)
        }
    }
}

Force parameters

Forces can define parameters which will be exposed in the config, as well as the editor as live sliders. These are attached as uniforms, per individual interaction definition (ex. for pairwise functions the config may define one set of parameters for hydrogen-hydrogen interactions, and another for hydrogen-oxygen).

See the config section of the docs for more info about defining force parameters.

Defining parameters

Use param<Float>("paramNameHere") to declare your function parameters, the type in brackets is a serializable type used to read the parameter from config.

Using parameters in your shader

To attach a passed parameter to your shader, use the asShaderParam() function provided in the createFunction() block (ex. val myShaderParam = myParameter.asShaderParam()).

Last modified: 08 March 2025