@woosh/meep-engine/src/engine/physics/fluid/solver/v3_grid_apply_advection_forward.js

Pure JavaScript game engine. Fully featured and production ready.

import { scs3d_sample_linear } from "../../../graphics/texture/3d/scs3d_sample_linear.js";

/**
 *
 * @param {Float32Array[]} outputs
 * @param {Float32Array[]} inputs
 * @param {number[]} resolution
 * @param {number} time_delta
 */
export function v3_grid_apply_advection_forward(outputs, inputs, resolution, time_delta) {

    const res_x = resolution[0];
    const res_y = resolution[1];
    const res_z = resolution[2];

    const input_x = inputs[0];
    const input_y = inputs[1];
    const input_z = inputs[2];

    const slice_size = res_y * res_x;

    for (
        let z = 0;
        z < res_z - 1;
        z++
    ) {

        const current_z_slice_offset = z * slice_size;

        for (
            let y = 0;
            y < res_y;
            y++
        ) {
            const current_y_line_offset = y * res_x;

            for (let x = 0; x < res_x; x++) {


                const current_index = current_z_slice_offset + current_y_line_offset + x;

                const v_x = input_x[current_index]
                const v_y = input_y[current_index]
                const v_z = input_z[current_index]

                // compute previous position of the particle
                const s_x = x - v_x * time_delta;
                const s_y = y - v_y * time_delta;
                const s_z = z - v_z * time_delta;

                // sample values at previous position
                const new_x = scs3d_sample_linear(input_x, res_x, res_y, res_z, s_x, s_y, s_z);
                const new_y = scs3d_sample_linear(input_y, res_x, res_y, res_z, s_x, s_y, s_z);
                const new_z = scs3d_sample_linear(input_z, res_x, res_y, res_z, s_x, s_y, s_z);

                outputs[0][current_index] = new_x;
                outputs[1][current_index] = new_y;
                outputs[2][current_index] = new_z;
            }
        }
    }
}