let c2d = null;
let raster_queue = [];

function init_rasterizer() {
    c2d = document.querySelector('#offscreen').getContext('2d'); 
    c2d.canvas.width = config.w;
    c2d.canvas.height = config.h;
    c2d.font = '16px ibm8x16';
    //c2d.font = '14px monospace';
    c2d.textAlign = 'center';
    c2d.textBaseline = 'middle';
    c2d.fillStyle = '#eeeeee';
}

function rasterize(text) {
    c2d.clearRect(0, 0, c2d.canvas.width, c2d.canvas.height); 
    c2d.fillText(text, config.w / 2, config.h / 2);
    //c2d.fillRect(0, 0, 32, 32);
}

function queue_rasterize(text, at) {
    raster_queue.push({'text': text, 'at': at});
}

function copy_canvas_to_texture(at) {
    gl.texSubImage2D(gl.TEXTURE_2D, 0, 
        at.x * config.w, at.y * config.h, 
        config.w, config.h, 
        gl.RGBA, gl.UNSIGNED_BYTE, 
        c2d.canvas
    );
}

function rasterize_and_upload_batch(batch_size) {
    let head = 0;

    gl.bindTexture(gl.TEXTURE_2D, textures['raster']);

    for (let i = 0; i < batch_size && i < raster_queue.length; ++i) {
        const entry = raster_queue[i];
        rasterize(entry.text);
        copy_canvas_to_texture(entry.at);
        head = i + 1;
    }

    raster_queue.splice(0, head);

    return raster_queue.length;
}