@woosh/meep-engine/src/engine/graphics/ecs/trail2d/makeGradientTrail.js

Pure JavaScript game engine. Fully featured and production ready.

import { assert } from "../../../../core/assert.js";
import {
    RIBBON_ATTRIBUTE_ADDRESS_AGE,
    RIBBON_ATTRIBUTE_ADDRESS_COLOR,
    RIBBON_ATTRIBUTE_ADDRESS_THICKNESS,
    RIBBON_ATTRIBUTE_ADDRESS_UV_OFFSET
} from "../../trail/x/ribbon_attributes_spec.js";
import Trail2D from "./Trail2D.js";
import { Trail2DFlags } from "./Trail2DFlags.js";

/**
 *
 * @param {number[]} color
 * @param {number[]} thickness
 * @param {number} [duration]
 * @param {number} [scale]
 * @param {number[]} position
 * @param {number[]} ages
 * @param {string} texture
 * @returns {Trail2D}
 */
export function makeGradientTrail({
                                      color,
                                      thickness,
                                      position,
                                      duration = 1,
                                      scale = 1,
                                      ages,
                                      texture
                                  }) {

    const trail2D = new Trail2D();
    trail2D.maxAge = duration;
    trail2D.width = 1;
    trail2D.textureURL = texture;

    const point_count = thickness.length;

    trail2D.build(point_count);

    const ribbon = trail2D.ribbon;

    for (let i = 0; i < point_count; i++) {

        const f = i / (point_count - 1);
        const i3 = i * 3;

        ribbon.setPointAlpha(i, 0);
        ribbon.setPointPosition(i, position[i3], position[i3 + 1], position[i3 + 2]);

        ribbon.setPointAttribute_Scalar(i, RIBBON_ATTRIBUTE_ADDRESS_AGE, ages[i] * duration);
        ribbon.setPointAttribute_Scalar(i, RIBBON_ATTRIBUTE_ADDRESS_UV_OFFSET, f);
        ribbon.setPointAttribute_Scalar(i, RIBBON_ATTRIBUTE_ADDRESS_THICKNESS, thickness[i]);

        const c_0 = color[i];

        assert.isNumber(c_0, `color[i]`);

        ribbon.setPointAttribute_Vector3(i, RIBBON_ATTRIBUTE_ADDRESS_COLOR, c_0 >> 16, c_0 >> 8, c_0);
    }

    // don't spawn more trail segments
    trail2D.clearFlag(Trail2DFlags.Spawning);
    trail2D.setFlag(Trail2DFlags.Built);

    ribbon.computeBoundingBox(trail2D.bvh.bounds);

    return trail2D;
}