乐趣区

关于前端:小程序canvas写一个简单的图片应用

jiezi

很早就想写一个挪动端图片小利用了，最近刚好休业在家，于是抽出工夫实现下本人的小想法

利用展现

截图

在线预览

需要

既然是小利用，那就心愿最终成品是有 实用的场景 且是 有价值 的

需要起源

这个利用需要的灵感

在以前工作生存中，常常会无心中取得共事的 美照

这时咱们想要把这张照片做成表情包

个别给图片增加几个阐明文字

一个有意思的沟通工具（表情包）就实现了

需要剖析

基于以上需要的拆解

能够将要利用性能实现整顿一下

  • 用户须要上传一张图片
  • 能够增加文字
  • 文字能够作 款式调整 和 旋转缩放
  • 另外咱们心愿还能够插入一些贴图
  • 贴图能够做 旋转缩放
  • 用户导出图片到相册

实现

github 仓库 https://github.com/luosijie/f…

如果喜爱我的我的项目，欢送给个星星激励一下

这个利用是用小程序开发的

  • 应用框架：mpx
  • 应用技术：小程序 canvas

状态治理

import {createStore} from '@mpxjs/core'

const store = createStore({
  state: {
    cavas: null,         // cnavas 实例
    ctx: null,           // canvas 上下文实例
    elements: [],        // canvas 元素
    activeIndex: null,   // 以后编辑中的元素索引
    mode: 'background',  // 以后编辑模式：background, text, sticker
    fontStyle: {         // 文字默认款式
      opacity: 1,
      fillStyle: '#000000',
      strokeStyle: '#000000'
    }
  },
  mutations: {setCanvas (state, data) {state.canvas = data},
    setCtx (state, data) {state.ctx = data},
    setElements (state, data) {state.elements = data},
    setMode (state, data) {state.mode = data},
    setActiveIndex (state, data) {state.activeIndex = data},
    setFontStyle (state, { key, data}) {state.fontStyle[key] = data
    },
    // 增加文字
    addText (state) {
      const size = 50
      const string = '请输出文字'
      const text = {
        type: 'text',
        data: string,
        scale: 1,
        size,
        left: 100,
        top: 100,
        rotate: 0,
        opacity: state.fontStyle.opacity,
        fillStyle: state.fontStyle.fillStyle,
        strokeStyle: state.fontStyle.strokeStyle
      }
      state.elements.push(text)
      state.activeIndex = state.elements.length - 1
    },
    // 增加贴图
    addSticker (state, data) {state.elements.push(data)
      state.activeIndex = state.elements.length - 1
    },
    // 删除以后选中
    deleteActiveELement (state) {state.elements.splice(state.activeIndex, 1)
      state.activeIndex = null
    },
    // 清空画布
    clear (state) {state.elements = []
      state.activeIndex = null
    }
  }
})

export default store

画布初始化

// 初始化画布
async initCanvas() {const query = this.createSelectorQuery()
  query
    .select('#canvas')
    .fields({node: true, size: true})
    .exec(async res => {const canvas = res[0].node
      const ctx = canvas.getContext('2d')
      store.commit('setCanvas', canvas)
      store.commit('setCtx', ctx)

      await this.loadImage('/images/icon-rotate.png').then(res => {this.image.rotate = res})

      canvas.width = res[0].width * this.dpr
      canvas.height = res[0].height * this.dpr
      ctx.scale(this.dpr, this.dpr)
      this.drawGrid()})
}

绘制图片

/**
 * 绘制图片
 * @param {Object} ele canvas 元素
 */
drawImage(ele) {this.ctx.save()
  const width = ele.width
  const height = ele.height
  const centerX = ele.left + ele.width / 2
  const centerY = ele.top + ele.height / 2
  this.ctx.translate(centerX, centerY)
  this.ctx.rotate(ele.rotate)
  this.ctx.drawImage(ele.data, ele.left - centerX, ele.top - centerY, width, height)
  this.ctx.restore()}

绘制文字

/**
 * 绘制文字
 * @param {Object} ele canvas 元素
 */
drawText(ele) {this.ctx.save()
  const width = ele.size * ele.data.length
  const height = ele.size
  const centerX = ele.left + width / 2
  const centerY = ele.top + height / 2
  this.ctx.translate(centerX, centerY)
  this.ctx.rotate(ele.rotate)
  this.ctx.font = `${ele.size}px bold sans-serif`
  this.ctx.globalAlpha = ele.opacity
  this.ctx.fillStyle = ele.fillStyle
  this.ctx.strokeStyle = ele.strokeStyle
  // this.ctx.lineWidth = 2
  this.ctx.textBaseline = 'top'
  console.log('draw-text', ele)
  this.ctx.fillText(ele.data, ele.left - centerX, ele.top - centerY)
  this.ctx.strokeText(ele.data, ele.left - centerX, ele.top - centerY)
  this.ctx.restore()}

绘制控制元件

initController(ele) {const cs = this.convert2ControllerSize(ele)
  this.ctx.save()
  this.ctx.strokeStyle = '#eee'
  this.ctx.translate(cs.centerX, cs.centerY)
  this.ctx.rotate(cs.rotate)
  // 绘制虚线边框
  this.ctx.setLineDash([10, 5], 5)
  this.ctx.strokeRect(cs.left - cs.centerX, cs.top - cs.centerY, cs.width, cs.height)
  // 绘制控制点 - 旋转
  this.ctx.drawImage(this.image.rotate, cs.left + cs.width - 10 - cs.centerX, cs.top + cs.height - 10 - cs.centerY, 20, 20)
  this.ctx.restore()}

画布渲染函数

// 画布渲染函数
renderCanvas() {this.ctx.clearRect(0, 0, this.ctx.canvas.width, this.ctx.canvas.height)
  this.drawGrid()
  console.log('draw-background', this.background)
  if (this.background) this.drawImage(this.background)
  for (let i = 0; i < this.elements.length; i++) {const ele = this.elements[i]
    // 渲染背景
    if (ele.type === 'background') {this.drawImage(ele)
    }
    if (ele.type === 'sticker') {this.drawImage(ele)
    }
    // 渲染文字
    if (ele.type === 'text') {this.drawText(ele)
    }
    // 选中元素增加控制元件
    if (this.activeIndex === i) {this.initController(ele)
    }
  }
}

事件监听

挪动

// 挪动事件绑定函数
handleMove(e) {console.log('mouse-move', e)
  if (e.touches.length > 1) return
  const x = e.touches[0].x
  const y = e.touches[0].y
  const dx = this.startTouches[0].x - x
  const dy = this.startTouches[0].y - y
  const elements = this.elements.slice()
  elements[this.activeIndex || 0].left = this.startSelected.left - dx
  elements[this.activeIndex || 0].top = this.startSelected.top - dy
  store.commit('setElements', elements)
}

旋转

// 旋转绑定函数
handleRotate(e) {console.log('handleRotate')
  const start = this.startTouches[0]
  const end = e.touches[0]
  const center = {
    x: this.startSelected.centerX,
    y: this.startSelected.centerY
  }
  const startLength = Math.sqrt((center.x - start.x) ** 2 + (center.y - start.y) ** 2)
  const endLength = Math.sqrt((center.x - end.x) ** 2 + (center.y - end.y) ** 2)
  const radian = this.convert2Radian(start, end, center)
  const scale = endLength / startLength
  const elements = this.elements.slice()
  const selected = elements[this.activeIndex]
  // 旋转
  selected.rotate = this.startSelected.rotate - radian
  // 缩放
  if (selected.type === 'text') {
    selected.left = this.startSelected.centerX - this.startSelected.size * this.startSelected.data.length * scale / 2
    selected.top = this.startSelected.centerY - this.startSelected.size * scale / 2
    selected.size = this.startSelected.size * scale
  }
  if (selected.type === 'sticker') {
    selected.left = this.startSelected.centerX - this.startSelected.width * scale / 2
    selected.top = this.startSelected.centerY - this.startSelected.height * scale / 2
    selected.width = this.startSelected.width * scale
    selected.height = this.startSelected.height * scale
  }
  store.commit('setElements', elements)
}

缩放

// 缩放事件绑定函数
handleScale(e) {if (e.touches.length !== 2 || this.mode !== 'background') return
  const startLength = Math.sqrt((this.startTouches[0].x - this.startTouches[1].x) ** 2 +
      (this.startTouches[0].y - this.startTouches[1].y) ** 2
  )
  const endLength = Math.sqrt((e.touches[0].x - e.touches[1].x) ** 2 + (e.touches[0].y - e.touches[1].y) ** 2
  )
  const scale = endLength / startLength
  const elements = this.elements.slice()
  const selected = elements[this.activeIndex || 0]
  selected.left = this.startSelected.centerX - this.startSelected.width * scale / 2
  selected.top = this.startSelected.centerY - this.startSelected.height * scale / 2
  selected.width = this.startSelected.width * scale
  selected.height = this.startSelected.height * scale
  // elements[this.activeIndex || 0].scale = this.startSelected.scale * scale
  store.commit('setElements', elements)
}

导出图片

export() {if (!store.state.elements.length) {
    wx.showToast({
      title: '加点货色再导出吧',
      icon: 'none'
    })
    return
  }
  wx.showModal({
    title: '提醒',
    content: '图片将保留到手机相册',
    success(res) {if (res.confirm) {console.log('export-canvas', store.state.ctx)
        const canvas = store.state.canvas
        wx.canvasToTempFilePath({
          x: 0,
          y: 0,
          width: canvas.width,
          height: canvas.height,
          canvas,
          complete(res) {if (res.errMsg === 'canvasToTempFilePath:ok') {
              wx.saveImageToPhotosAlbum({
                filePath: res.tempFilePath,
                success(res) {
                  wx.showToast({
                    title: '图片保留胜利',
                    icon: 'none'
                  })
                }
              })
            }
          }
        })
      }
    }
  })
}

我的项目继续更新优化，感兴趣的敌人能够关注一下，一起交流学习

github 仓库 https://github.com/luosijie/f…

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