Helper functions for ImpactJS to double or halve the tilesize of a BackgroundMap (without breaking their appearance)

impact-edit-map-util.ts

export function halveTilesize( layer: Layer, tileset: Image ) {
    if( layer.tilesize % 2 !== 0 || (layer.name !== 'collision' && !tileset.loaded) ) {
        return false;
    }

    const oldTileWidth = tileset.width / layer.tilesize;
    const newTileWidth = (tileset.width / layer.tilesize) * 2;
    const newData = [];
    for( let y = 0; y < layer.height; y++ ) {
        newData[y * 2] = [];
        newData[y * 2 + 1] = [];
        for( let x = 0; x < layer.width; x++ ) {
            const oldTile = layer.data[y][x] - 1;
            if( oldTile === -1 ) { // Empty tile
                newData[y * 2][x * 2]         = 0;
                newData[y * 2][x * 2 + 1]     = 0;
                newData[y * 2 + 1][x * 2]     = 0;
                newData[y * 2 + 1][x * 2 + 1] = 0;
            } else {
                let a: number, b: number, c: number, d: number;
                if (layer.name === 'collision') {
                    a = b = c = d = oldTile + 1;
                } else {
                    const oldTilesetY = Math.floor(oldTile / oldTileWidth);
                    const oldTilesetX = oldTile - oldTilesetY * oldTileWidth;
                    const newTilesetX = oldTilesetX * 2;
                    const newTilesetY = oldTilesetY * 2;
                    a = (newTilesetY + 0) * newTileWidth + (newTilesetX + 0) + 1;
                    b = (newTilesetY + 0) * newTileWidth + (newTilesetX + 1) + 1;
                    c = (newTilesetY + 1) * newTileWidth + (newTilesetX + 0) + 1;
                    d = (newTilesetY + 1) * newTileWidth + (newTilesetX + 1) + 1;
                }
                newData[y * 2][x * 2] = a;
                newData[y * 2][x * 2 + 1] = b;
                newData[y * 2 + 1][x * 2] = c;
                newData[y * 2 + 1][x * 2 + 1] = d;
            }
        }
    }

    layer.tilesize /= 2;
    layer.width *= 2;
    layer.height *= 2;
    layer.data = newData;

    return true;
}

export function doubleTilesize( layer: Layer, tileset: Image ) {
    if( layer.width % 2 !== 0 || layer.height % 2 !== 0 || (layer.name !== 'collision' && !tileset.loaded) ) {
        return false;
    }

    const oldTileWidth = tileset.width / layer.tilesize;
    const newTileWidth = (tileset.width / layer.tilesize) / 2;
    if( newTileWidth % 1 !== 0 ) {
        return false;
    }

    const newData = [];
    for( let y = 0; y < layer.height; y += 2 ) {
        newData[y / 2] = [];
        for( let x = 0; x < layer.width; x += 2 ) {
            const oldTile = layer.data[y][x] - 1;
            if( oldTile === -1 ) { // Empty tile
                newData[y / 2][x / 2] = 0;
            } else {
                if(layer.name === 'collision') {
                    newData[y / 2][x / 2] = oldTile + 1;
                } else {
                    const oldTilesetY = Math.floor(oldTile / oldTileWidth);
                    const oldTilesetX = oldTile - oldTilesetY * oldTileWidth;
                    const newTilesetX = oldTilesetX / 2;
                    const newTilesetY = oldTilesetY / 2;
                    newData[y / 2][x / 2] = newTilesetY * newTileWidth + newTilesetX + 1;
                }
            }
        }
    }

    layer.tilesize *= 2;
    layer.width /= 2;
    layer.height /= 2;
    layer.data = newData;

    return true;
}