pbm.js

// BEWARE: THERE ARE SOME VERY SKETCHY BITS AHEAD!
// Never ever use, anywhere, outside of this project.
const fs = require("fs");

module.exports = class {

    constructor(filename, bytesPerPixel) {

        if(bytesPerPixel != 1 && bytesPerPixel != 2) throw new Error("unsupported bit depth");

        // read full file
        this.data = fs.readFileSync(filename);
        this.offset = 0;

        // read properties
        if(this.readLine() != "P6") throw new Error("Magic string doesn't match");
        this.width = Number(this.readLine());
        this.height = Number(this.readLine());
        this.max = Number(this.readLine());
        this.bytesPerPixel = bytesPerPixel;

        // read image data
        this.data = this.data.slice(this.offset, this.data.length);
        this.pixels = new Float32Array(this.width * this.height * 3);
        for(let x = 0; x < this.width; x++) {
            for(let y = 0; y < this.height; y++) {

                const pixelIdx = (y * this.width + x) * 3;
                const idx = pixelIdx * this.bytesPerPixel;
                let r, g, b;

                if(this.bytesPerPixel == 2) {
                    r = this.data.readUInt16BE(idx);
                    g = this.data.readUInt16BE(idx + 2);
                    b = this.data.readUInt16BE(idx + 4);
                } else {
                    r = this.data[idx];
                    g = this.data[idx + 1];
                    b = this.data[idx + 2];
                }

                this.pixels[pixelIdx] = r / this.max;
                this.pixels[pixelIdx + 1] = g / this.max;
                this.pixels[pixelIdx + 2] = b / this.max;

            }
        }

        this.data = null;
        console.log("finished reading " + filename);

    }

    write(name) {
        const stream = fs.createWriteStream(name);
        stream.write(`P6\n${this.width}\n${this.height}\n${this.max}\n`);
        for(let y = 0; y < this.height; y++) {
            for(let x = 0; x < this.width; x++) {
                const pixelIdx = (y * this.width + x) * 3;
                const r = this.pixels[pixelIdx], g = this.pixels[pixelIdx + 1], b = this.pixels[pixelIdx + 2];
                if(this.max > 256) {
                    const pixbuf = Buffer.allocUnsafe(6);
                    pixbuf.writeUInt16BE(r * this.max, 0);
                    pixbuf.writeUint16BE(g * this.max, 2);
                    pixbuf.writeUint16BE(b * this.max, 4);
                    stream.write(pixbuf.slice(0, 6));
                } else {
                    const pixbuf = Buffer.allocUnsafe(3);
                    pixbuf.writeUint8(r * this.max, 0);
                    pixbuf.writeUint8(g * this.max, 1);
                    pixbuf.writeUint8(b * this.max, 2);
                    stream.write(pixbuf.slice(0, 3));
                }
                
            }
        }
        stream.end();
    }

    readLine() {
        for(let i = this.offset; i < this.data.length; i++) {
            if(this.data[i] == 0xA) {
                const result = this.data.slice(this.offset, i);
                this.offset = i + 1;
                return result.toString("utf-8");
            }
        }
        throw new Error("Unexpectedly reached end of file");
    }

    forEachPixel(func) {
        for(let x = 0; x < this.width; x++) {
            for(let y = 0; y < this.height; y++) {
                const idx = (y * this.width + x) * 3;
                func(
                    this.pixels[idx], this.pixels[idx + 1], this.pixels[idx + 2], // normalized RGB
                    idx,
                    x, y // coordinates
                );

            }
        }
    }

    getPixel(x, y) {
        const idx = (y * this.width + x) * 3;
        return [this.pixels[idx], this.pixels[idx + 1], this.pixels[idx + 2]];
    }

    filter(func) {
        this.forEachPixel((r, g, b, idx, x, y) => {
            [this.pixels[idx], this.pixels[idx + 1], this.pixels[idx + 2]] = func(r, g, b, x, y);
        });
    }

};