scratch-sb1-converter/src/coders/png-file.js

Scratch 1 (.sb) to Scratch 2 (.sb2) conversion library for Scratch 3.0

import {ByteStream} from './byte-stream';
import {PNGSignature, PNGIHDRChunkBody, PNGFilterMethodByte} from './png-packets';
import {DeflateStream} from './deflate-stream';
import {PNGChunkStream} from './png-chunk-stream';

class PNGFile {
    encode (width, height, pixelsUint8) {
        const rowSize = (width * 4) + PNGFilterMethodByte.size;
        const bodySize = rowSize * height;
        const size = (
            PNGSignature.size +
            // IHDR
            PNGChunkStream.size(PNGIHDRChunkBody.size) +
            // IDAT
            PNGChunkStream.size(DeflateStream.estimateSize(bodySize)) +
            // IEND
            PNGChunkStream.size(0)
        );

        const stream = new ByteStream(new ArrayBuffer(size));

        stream.writeStruct(PNGSignature, {
            support8Bit: 0x89,
            png: 'PNG',
            dosLineEnding: '\r\n',
            dosEndOfFile: '\x1a',
            unixLineEnding: '\n'
        });

        const pngIhdr = new PNGChunkStream(stream, 'IHDR');

        pngIhdr.writeStruct(PNGIHDRChunkBody, {
            width,
            height,
            bitDepth: 8,
            colorType: 6,
            compressionMethod: 0,
            filterMethod: 0,
            interlaceMethod: 0
        });

        pngIhdr.finish();

        const pngIdat = new PNGChunkStream(stream, 'IDAT');

        const deflate = new DeflateStream(pngIdat);

        let pixelsIndex = 0;
        while (pixelsIndex < pixelsUint8.length) {
            deflate.writeStruct(PNGFilterMethodByte, {
                method: 0
            });

            const partialLength = Math.min(
                pixelsUint8.length - pixelsIndex,
                rowSize - PNGFilterMethodByte.size
            );
            deflate.writeBytes(
                pixelsUint8, pixelsIndex, pixelsIndex + partialLength
            );

            pixelsIndex += partialLength;
        }

        deflate.finish();

        pngIdat.finish();

        const pngIend = new PNGChunkStream(stream, 'IEND');

        pngIend.finish();

        return stream.buffer;
    }

    static encode (width, height, pixels) {
        return new PNGFile().encode(width, height, pixels);
    }
}

export {PNGFile};