//draw a line between two points on canvas
function line(x0, y0, x1, y1, brushSize) {

    var dx = Math.abs(x1-x0);
    var dy = Math.abs(y1-y0);
    var sx = (x0 < x1 ? 1 : -1);
    var sy = (y0 < y1 ? 1 : -1);
    var err = dx-dy;

    while (true) {
        //set pixel
        // If the current tool is the brush
        if (currentTool == 'pencil' || currentTool == 'rectangle') {
            // I fill the rect
            currentLayer.context.fillRect(x0-Math.floor(brushSize/2), y0-Math.floor(brushSize/2), brushSize, brushSize);
        } else if (currentTool == 'eraser') {
            // In case I'm using the eraser I must clear the rect
            currentLayer.context.clearRect(x0-Math.floor(eraserSize/2), y0-Math.floor(eraserSize/2), eraserSize, eraserSize);
        }

        //if we've reached the end goal, exit the loop
        if ((x0==x1) && (y0==y1)) break;
        var e2 = 2*err;
        if (e2 >-dy) {err -=dy; x0+=sx;}
        if (e2 < dx) {err +=dx; y0+=sy;}
    }
}

// draw a line between two points on canvas
function lineOnLayer(x0, y0, x1, y1, brushSize, context) {

    var dx = Math.abs(x1-x0);
    var dy = Math.abs(y1-y0);
    var sx = (x0 < x1 ? 1 : -1);
    var sy = (y0 < y1 ? 1 : -1);
    var err = dx-dy;

    while (true) {
        //set pixel
        // If the current tool is the brush
        if (currentTool == 'pencil' || currentTool == 'rectangle') {
            // I fill the rect
            context.fillRect(x0-Math.floor(brushSize/2), y0-Math.floor(brushSize/2), brushSize, brushSize);
        } else if (currentTool == 'eraser') {
            // In case I'm using the eraser I must clear the rect
            context.clearRect(x0-Math.floor(eraserSize/2), y0-Math.floor(eraserSize/2), eraserSize, eraserSize);
        }

        // if we've reached the end goal, exit the loop
        if ((x0==x1) && (y0==y1)) break;
        var e2 = 2*err;
        if (e2 >-dy) {err -=dy; x0+=sx;}
        if (e2 < dx) {err +=dx; y0+=sy;}
    }
}