functions deleting the paint canvas

Tags: , ,



I would really appreciate If someone could figure out what is wrong with my functions. I’m working on this simple paint program and I have Undo and Clear buttons. Undo is supposed to clear the last drawn line (the function deletes the last element of the array since the array consist of all the drawn lines on the canvas) and Clear just takes the canvas back to It’s formal state (makes the board completely white). But every time I put any of those functions in the code my canvas just deletes Itself and I can’t seem to figure out what’s wrong. The function names are clear_canvas and undo_last. Any tips or solutions on how to fix or make another working example?

<head>
    <img src="logo.png" style="width:50%; margin-right: auto; margin-left: 400px; ">
</head>

<style>

body, a, a:hover { cursor:url('https://66.media.tumblr.com/7659e714cab33f9d59124f924405e793/tumblr_inline_p7g82dZq1h1r466gz_75sq.png'), auto 
}

body {
  transform-style: preserve-3d;
  background-image: url('img_girl.jpg');
  background-repeat: no-repeat;
  background-attachment: fixed;
}



canvas {
    cursor: pointer;
    display: block;
    margin-left: auto;
    margin-right: auto;
    margin-top: 200px;
    padding: 5px;

}


.tools .color-field {
    height:  40px;
    width: 40px;
    cursor:  pointer;
    display:  inline-block;
    box-sizing:  border-box;
    border-radius: 50%;
    border: 2px solid white;
    align-self:  center;
    margin: 5px 5px ;


}


.color-field {

    display: block;
    margin-left: auto;
    margin-right: auto;

}


.tools {
    display: flex;
    justify-content: center;
    flex-direction: row;
    margin-top: 110px;
}

.tools .button{
    align-self:  center;
    width: 100px;
    height: 40px;
    border: 2px solid white;
    cursor:  pointer;
    color: white;
    background: #DB7093;
    font-weight: bold;
    margin:  0 10px;
    display: block;

}


.button {

    display: block;
    margin-left: auto;
    margin-right: auto;
}


.color-picker {
    align-self: center;
    margin: 0 15px;
    background-color: pink;
}

.pen-range {
    align-self:  center;
    margin:  o 15px;
    background-color: #DB7093;

}


.container {
  width: 600px;
  display: block;
  margin-left: auto;
  margin-right: auto;
  position: absolute;
  z-index:-1;
  margin-left:  425px;


}

#gif {
background-image: url("gif.gif");
position: fixed;
width:  100%;
transform: translateZ(-1px);
top: 0;
left: 0;

  
}


</style>


<body style="background-image: url('https://images8.alphacoders.com/105/1055726.png');">


<div id="gif"> <img src="gif.gif"> </div>


<meta charset="UTF-8"/>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title> cute drawing program </title>



<div class="container">
  <div id="status" style="color: white;"></div>
  <img src="container.png" style="width:120%;">
</div>


<div class="field">
<canvas id="canvas"> </canvas>

<div class="tools">
<button onClick="undo_last()" type="button" class="button"> Undo </button>
<button onClick="clear_canvas()" type="button" class="button"> Clear </button>


<div onClick="change_color(this)" class="color-field" style="background: red;"></div>
<div onClick="change_color(this)" class="color-field" style="background: blue;"></div>
<div onClick="change_color(this)" class="color-field" style="background: yellow;"></div>
<div onClick="change_color(this)" class="color-field" style="background: green;"></div>
<div onClick="change_color(this)" class="color-field" style="background: orange;"></div>
<div onClick="change_color(this)" class="color-field" style="background: pink;"></div>
<div onClick="change_color(this)" class="color-field" style="background: brown;"></div>
<div onClick="change_color(this)" class="color-field" style="background: gray;"></div>  
<div onClick="change_color(this)" class="color-field" style="background: black;"></div>
<div onClick="change_color(this)" class="color-field" style="background: white;"></div>

<input onInput="draw_color = this.value" type="color" class="color-picker">
<input type="range" min="1" max="100" class="pen-range" onInput="draw_width = this.value">
</div>
</div>

<script>
    
    const canvas = document.getElementById("canvas");
    canvas.width = window.innerWidth = 650;
    canvas.height = 350;

    let context = canvas.getContext("2d");
    let start_background_color ="white";
    context.fillStyle = start_background_color;
    context.fillRect(0, 0, canvas.width, canvas.height);
    
    
    let draw_color = "black";
    let draw_width = "2";
    let is_drawing = false;
    
    let restore_array =[];
    let index = -1;


    function change_color(element) {
        draw_color = element.style.background;
    }

    canvas.addEventListener("touchstart", start, false);
    canvas.addEventListener("touchmove", draw, false);
    canvas.addEventListener("mousedown", start, false);
    canvas.addEventListener("mousemove", draw, false);

    canvas.addEventListener("mtouchstart", stop, false);
    canvas.addEventListener("mouseup", stop, false);
    canvas.addEventListener("mouseout", stop, false);


    function start(event) {
        is_drawing = true;
        context.beginPath();
        context.moveTo(event.clientX - canvas.offsetLeft,
                       event.clientY - canvas.offsetTop);

    event.preventDefault();
    }

function draw(event) {
    if ( is_drawing ) {
        context.lineTo(event.clientX - canvas.offsetLeft,
                       event.clientY - canvas.offsetTop);
        context.strokeStyle = draw_color;
        context.lineWidth = draw_width;
        context.lineCap = "round";
        context.lineJoin = "round";
        context.stroke();
    }

    event.preventDefault();
}


function stop(event) {
    if (is_drawing) {
        context.stroke();
        context.closePath();
        is_drawing = false;
    }

    event.preventDefault();


    if (event.type != 'mouseout'){
    restore_array.push(context.getImageData(0, 0, canvas.width, canvas.height));
    index += 1;
    }
}

 function undo_last(){
     if (index <= 0) {
        clear_canvas();
     }
     else {
        index -=1;
        restore _array.pop();
        context.putImageData(restore_array[index], 0, 0);

        }

     }


function clear_canvas() {
    context.fillStyle = start_background_color;
    context.clearRect(0, 0, canvas.width, canvas.height);
    context.fillRect(0, 0, canvas.width, canvas.height);

    restore_array = [];
    index = -1;
} 


</script>



</body>







</html>

Answer

You should use console.log. You should also be getting an error that helps identify your issue when you run the script.

Check this line in undo_last

restore _array.pop();

It should be

restore_array.pop();


Source: stackoverflow