為什麼我的繪圖畫佈在頁面內偏移？

Question

這很難解釋。但我會嘗試，整個畫布都是偏移的。我不確定這是怎麼發生的或如何解決它。就像當您的滑鼠位於頁面的左上角並且您從中心開始時，它與畫布元素本身的左上角相符。使用程式碼片段來了解我在說什麼。

let currentColor = null;

let inputs = document.getElementsByClassName("style2");

for (const input of inputs) {
  input.addEventListener("click", (e) => {
    if (e.detail !== 2) e.preventDefault();
  });
}


let arr = [];

for (let i = 0; i < inputs.length + 1; i++) {
  arr.push(i.toString());
}
arr.shift();

for (const input of inputs) {
  input.addEventListener("input", (e) => {
    const { value } = document.getElementById(e.target.id);
    currentColor = value;
    $("#selectedColor").css("background-color", value);
  })
    input.addEventListener("click", (e) => {
    const { value }  = document.getElementById(e.target.id);
    currentColor = value;
    $("#selectedColor").css("background-color", value);
  })
}

var rangeslider = document.getElementById("sliderRange");
const setSize = document.getElementById("setSize")
const submit = document.getElementById("submit")

submit.addEventListener("click", (e) => {
  rangeslider.value = setSize.value 
})

const button = document.getElementById("clear")
// create canvas element and append it to document body
var canvas = document.getElementById('canvas');
// some hotfixes... ( ≖_≖)
// get canvas 2D context and set him correct size
var ctx = canvas.getContext('2d');
resize();

// last known position
var pos = { x: 0, y: 0 };

window.addEventListener('resize', resize);
button.addEventListener('click', clear)
document.addEventListener('mousemove', draw);
document.addEventListener('mousedown', setPosition);
document.addEventListener('mousemove', setPosition);


// new position from mouse event
function setPosition(e) {
  let canvas = document.getElementById("canvas")
  pos.x = e.clientX
  pos.y = e.clientY
}

// resize canvas
function resize() {
  ctx.canvas.width = 650;
  ctx.canvas.height = 375;
}

function draw(e) {
  // mouse left button must be pressed
  if (e.buttons !== 1) return;
  let canvas = document.getElementById('canvas');

  console.log(pos)
  ctx.beginPath(); // begin

  ctx.lineWidth = rangeslider.value;
  ctx.lineCap = 'round';
  ctx.strokeStyle = currentColor;

  ctx.moveTo(pos.x, pos.y); // from
  setPosition(e);
  ctx.lineTo(pos.x, pos.y); // to

  ctx.stroke(); // draw it!
}

function clear() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
}

html, body {
  height: 100%;
  width: 100%;
  font-family: sans-serif;
  background-color: #B3B7B5;
/*   overflow: hidden; */
}

.style2 {
  -webkit-appearance: none;
  -moz-appearance: none;
  appearance: none;
  background-color: transparent;
  width: 35px;
  height: 35px;
  border: none;
  cursor: pointer;
}


.style2::-webkit-color-swatch {
  border-radius: 50%;
  border: 3px solid #000000;
}
.style2::-moz-color-swatch {
  border-radius: 50%;
  border: 3px solid #000000;
}

.box {
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  justify-content: center;
  align-items: center;
  gap: 5px;
  max-width: 320px;
  margin: 0 auto;
  padding: 7.5px 10px;
}

.box1 {
    display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  justify-content: center;
  align-items: center;
  gap: 5px;
  max-width: 9999px;
  margin: 0 auto;
  padding: 10px 10px;
}

.box5 {
    display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  justify-content: center;
  align-items: center;
  gap: 5px;
  max-width: 650px;
  margin: 0 auto;
  padding: 10px 10px;
}

.box2 {
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  justify-content: center;
  align-items: center;
  gap: 5px;
  max-width: 9999px;
  margin: 0 auto;
  padding: 10px 10px;
}

#selectedColor {
  width: 100px;
  height: 30px;
  border: 3px solid black;
  border-radius: 5px;
  background-color: black;
}

.canvas {
  height: 350px;
  width: 650px;
  border: 3px solid black;
  border-radius: 5px;
  background-color: white;
  cursor: crosshair;
  position: relative;
/*   left: 50%; */
}

#clear {
  width: 50px;
  height: 35px;
  font-size: 15px;
  border-radius: 5px;
}

#submit {
  width: 59px;
  height: 23px;
  margin: auto;
  left: 35%;
  border-radius: 5px;
  position: relative;
}

.rangeslider {
    width: 50%;
}
  
.myslider {
    -webkit-appearance: none;
    background: #FCF3CF  ;
    width: 50%;
    height: 20px;
    opacity: 2;
   }
  
  
.myslider::-webkit-slider-thumb {
    -webkit-appearance: none;
    cursor: pointer;
    background: #34495E  ;
    width: 5%;
    height: 20px;
}
  
  
.myslider:hover {
    opacity: 1;
}

.rangeslider {
  left: 38%;
  position: absolute;
}

<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>replit</title>
  <link href="style.css" rel="stylesheet" type="text/css" />
</head>

<body>
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

  <div class="box5">
    <canvas class="canvas" id="canvas"></canvas>
  </div>
  
  <div class="box1">
    <button id="clear">Clear</button><br>
  </div>

  <div class="box1">
    <div class="rangeslider">
          <input type="range" min="1" max="100" value="5" class="myslider" id="sliderRange">
    </div>
  </div>
  <div class=box1>
    <div>
      <input id="setSize" type="text" placeholder="Set Brush Size... (Max 100)">
      <br>
      <button type="submit" id="submit" for="setSize">Submit</button>
    </div>
  </div>
  
  <div class="box">
      <div class="container">
        <input type="color" value="#000000" class="style2" id="1" />
      </div>
      <div class="container">
        <input type="color" value="#ffffff" class="style2" id="2" />
      </div>
      <div class="container">
        <input type="color" value="#ffffff" class="style2" id="3" />
      </div>
      <div class="container">
        <input type="color" value="#ffffff" class="style2" id="4" />
      </div>
      <div class="container">
        <input type="color" value="#ffffff" class="style2" id="5" />
      </div>
  </div>

  <div class="box">
    <label for="selectedColor">Current Color:</label>
    <div id="selectedColor"></div>
  </div>

  <script src="script.js"></script>
</body>

</html>
 

我知道這段程式碼有點奇怪，但請告訴我。

Answer 1

計算滑鼠位置的方式不太合適，需要考慮到畫布相對於視窗的偏差。您不能使用 getBoundingClientRect() 來做到這一點：

function setPosition(e) {
  const canvas = document.getElementById("canvas");
  const bounds = canvas.getBoundingClientRect();
  pos.x = e.clientX - bounds.left;
  pos.y = e.clientY - bounds.top;
}

但是您還必須透過刪除寬度和高度或設定與調整大小函數中相同的高度來修復 .canvas css 類別。

https://codepen.io/Joulss/pen/BaPYgpZ?editors=1111

Answer 2

這其實是一個很容易解決的問題。您只是忘記偏移 clientX 和 clientY。您會看到，這些座標位於視窗空間中，因此 (0,0) 將位於視窗的左上角。如果您的畫布也在左上角，那麼一切看起來都很好，但在您的情況下，畫布位於中心，因此座標不會對齊。這可以透過將座標減去畫布的螢幕位置來修復。

這是一個例子：

function setPosition(e) {
  let canvas = document.getElementById("canvas")
  let bounds = canvas.getBoundingClientRect()
  pos.x = e.clientX - bounds.x
  pos.y = e.clientY - bounds.y
}

您可以在https://developer.mozilla.org/en-US/docs/Web/API/Element/getBoundingClientRect" rel="nofollow noreferrer">https:// /developer.mozilla.org /en-US/docs/Web/API/Element/getBoundingClientRect