时间戳

首页 > 解决方案 > 为什么我无法在画布上正确绘制

javascript - 为什么我无法在画布上正确绘制

问题描述

我正在开发一个油漆应用程序。当我将画板放置在屏幕的左侧时，我能够正确绘制。但是当我将它放在屏幕的右侧时，鼠标不会在它所在的位置绘制，而是在它右侧 100 px 之外。我开发了一个拖动功能，它可以让我将绘图应用程序的窗口拖动到屏幕中的不同位置。我正在使用香草 Javascript 和自定义元素。

const template = document.createElement('template')
template.innerHTML = `
<head>
<link rel="stylesheet" href="../css/paint-board.css">
</head>
<div id="board">
<div class="navbar">
<img id="pic" src="../image/tools.png" alt="paint" />
<img id="close" src="../image/error.png" alt="close window" />
</div>
<div id="bucketDiv" class="colour">
<img id="bucket" src="../image/paint-bucket.png" alt="bucket" />
</div>
</div>
<div id="paint">
<canvas id="canvasDrawing">
</canvas>
</div>
</div>
`
export class PaintBoard extends window.HTMLElement {
  constructor () {
    super()
    this.attachShadow({ mode: 'open' })
    this.shadowRoot.appendChild(template.content.cloneNode(true))
    this.x = 0
    this.y = 0
    window.colour = 'black'
    const canvas = this.shadowRoot.querySelector('#canvasDrawing')
    window.ctx = canvas.getContext('2d')
  }

  connectedCallback () {
    this.initialize()
    this.closeWindow()
    this.changeColour()
    this.changeLineWidth()
    this.changeBackground()
  }

  closeWindow () {
    const close = this.shadowRoot.querySelector('#board')
    close.addEventListener('click', event => {
      if (event.target === this.shadowRoot.querySelector('#close')) {
        close.classList.add('removed')
      }
    })
  }

  // intialize drawing on the board
  initialize () {
    const paintingBoard = this.shadowRoot.querySelector('#paint')
    this.size()
    paintingBoard.addEventListener('mousemove', event => {
      event.stopImmediatePropagation()
      this.draw(event)
    })
    paintingBoard.addEventListener('mousedown', event => {
      event.stopImmediatePropagation()
      this.setPosition(event)
    })
    paintingBoard.addEventListener('mouseenter', event => {
      this.setPosition(event)
    })
    dragElement(this.shadowRoot.querySelector('#board'))
  }

  draw (e) {
    if (e.buttons !== 1) return // if mouse is pressed.....
    window.ctx.beginPath() // begin the drawing path
    window.ctx.lineCap = 'round' // rounded end cap
    window.ctx.strokeStyle = window.colour // hex color of line
    window.ctx.moveTo(this.x, this.y) // from position
    this.x = e.clientX
    this.y = e.clientY
    window.ctx.lineTo(this.x, this.y) // to position
    window.ctx.stroke() // draw it!
  }

  // size canvas
  size () {
    window.ctx.canvas.width = 750
    window.ctx.canvas.height = 510
  }

  // new position from mouse events
  setPosition (e) {
    this.x = e.clientX
    this.y = e.clientY
  }

标签： javascripthtmlcsscanvas

解决方案

// where canvas is your canvas element
const rect = canvas.getBoundingClientRect();
this.x = e.pageX - window.pageXOffset - rect.left;
this.y = e.pageY - window.pageYOffset - rect.top;

为我工作，希望它对你有用。

e.pageX/e.pageY将获得鼠标在整个页面上的坐标。

window.pageXOffset/window.pageYOffset将为您提供用户到目前为止滚动的数量。

rect.left/会给你元素rect.top左上角的坐标canvas

e.pageY - window.pageYOffset= 鼠标在窗口中的位置

e.pageY - window.pageYOffset - rect.top= 鼠标在画布内的位置

推荐阅读