@woosh/meep-engine/src/engine/graphics/shaders/glsl_gen_swizzled_read.js

Pure JavaScript game engine. Fully featured and production ready.

/**
 *
 * @param {string} input name of the variable on which components are being accessed
 * @param {(string|number)[]} swizzle
 * @returns {string} swizzled vector
 */
export function glsl_gen_swizzled_read(input, swizzle) {
    const swizzle_read = [];
    const n = swizzle.length;
    for (let i = 0; i < n; i++) {
        const token = swizzle[i];

        if (typeof token === "string") {
            swizzle_read[i] = `${input}.${token}`;
        } else if (typeof token === "number") {
            swizzle_read[i] = Number(token).toFixed(4);
        } else {
            throw new Error(`Unsupported swizzle token '${token}'`);
        }
    }

    const arg_string = swizzle_read.join(', ');

    const ctors = [
        undefined,
        'float',
        'vec2',
        'vec3',
        'vec4'
    ];

    const ctor = ctors[swizzle.length];

    if (ctor === undefined) {
        throw new Error(`No constructor for input length ${swizzle.length}`);
    }

    return `${ctor}(${arg_string})`;
}