spriteplugin.js

const CW = 6;
const CH = 7;

function readSprites({readFileSync, resolveRelative}, filename) {
    const buf = readFileSync(resolveRelative(filename.lit));
    const numSprites = buf.readUInt8(4);
    const data = [];
    for (let i = 0; i < numSprites; i++) {
        const offs = i*64+9;
        const bytes = [];
        for (let j = 0; j < 64; j++) {
            bytes.push(buf.readUInt8(offs + j));
        }
        data.push(bytes);
    }
    return {
        numSprites,
        enableMask: (1<<numSprites)-1,
        bg: buf.readUInt8(6),
        multicol1: buf.readUInt8(7),
        multicol2: buf.readUInt8(8),
        data
    };
}

function swap(a) {
    const b = ((a & 0b11110000) >> 4) | ((a & 0b00001111) << 4);
    return ((b & 0b11001100) >> 2) | ((b & 0b00110011) << 2);
}

function readPix(data, x, y) {
    const row = swap(data[y*3]) | (swap(data[y*3+1])<<8) | (swap(data[y*3+2])<<16);
    let bitoffs = x * 2;
    return (row >> bitoffs) & 3;
}

function appendChar(out, data, cx, cy) {
    for (let y = 0; y < CH; y++) {
        let row = 0;
        for (let x = 0; x < CW; x++) {
            row |= readPix(data, cx + x, cy + y) << (x * 2);
        }
        out.push(swap(row) & 255);
        out.push(swap(row>>8) & 255);
    }
}

// Blit into sprite layout, just to test it produces the right kind of sprites.
function makeTestData(font) {
    const dst = Array(3*21).fill(0);
    for (let y = 0; y < 3; y++) {
        const ydst = 3*7*y;

        for (let yy = 0; yy < 7; yy++) {
            dst[ydst + yy*3 + 0] = font[(y*7+yy)*2 + 0]
            dst[ydst + yy*3 + 1] = font[(y*7+yy)*2 + 1]
        }
    }
    return dst;
}

// unpack sprites from the following format
//
// 000000111111  <-- sprite 0 rows 0-6
// 000000111111
// 000000111111
// 000000111111
// 000000111111
// 000000111111
// XXXXXXXXXXXX
// 222222333333 <-- sprite 0 rows 7-13
// 222222333333
// 222222333333
// 222222333333
// 222222333333
// 222222333333
// XXXXXXXXXXXX
//  -"- for 3rd sprite 0 chars
//
// ..to a an array of [[0,0], [1,1], [2,2]] (flattened)
// where 0,1,2 refer to letter indices.
module.exports = (ctx, filename) => {
    const {
        numSprites,
        bg,
        multicol1,
        multicol2,
        data
    } = readSprites(ctx, filename);
    const fontData = []
    for (let si = 0; si < numSprites; si++) {
        // Loop over chars
        for (let cy = 0; cy < 3; cy++) {
            for (let cx = 0; cx < 2; cx++) {
                // Blit one char to output
                appendChar(fontData, data[si], cx*CW, cy*CH);
            }
        }
    }
    return {
        numChars: numSprites*6,
        fontData,
        testData: makeTestData(fontData)
    }
}