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关于canvas:canvas画板之画笔的多种效果

前言

我之前做了一个画板,曾经迭代了两个版本,但既然是画板,如果只有一种画笔就显得太枯燥了,我就收罗了一下网上的各种计划和本人的一些想法,目前做出了 5 种款式,包含根底的总共 6 种,当然有了一些思路后,后续会持续减少。我会在本文具体阐明实现思路和具体代码,6 种款式包含:

  1. 根底单色
  2. 荧光
  3. 多色画笔
  4. 喷雾
  5. 蜡笔
  6. 泡泡

预览

预览地址:https://songlh.top/paint-board/
源码:https://github.com/LHRUN/paint-board 欢送 Star⭐️

根底单色

画笔的根底实现,除了点与点之间的连贯,还须要留神两点

  1. 首先是在鼠标挪动时计算以后挪动的速度,而后依据速度计算线宽,这个是为了实现鼠标挪动快,线宽就变窄,挪动慢,线宽就恢复正常这个成果
  2. 为了防止直线连接点成果不好,我会采纳贝塞尔曲线进行连贯
/**
 * 鼠标挪动时增加新的坐标
 * @param position
 */
addPosition(position: MousePosition) {this.positions.push(position)
  // 解决当火线宽
  if (this.positions.length > 1) {
    // 计算挪动速度
    const mouseSpeed = this._computedSpeed(this.positions[this.positions.length - 2],
      this.positions[this.positions.length - 1]
    )
    // 计算线宽
    const lineWidth = this._computedLineWidth(mouseSpeed)
    this.lineWidths.push(lineWidth)
  }
}

/**
 * 计算挪动速度
 * @param start 终点
 * @param end 起点
 */
_computedSpeed(start: MousePosition, end: MousePosition) {
  // 获取间隔
  const moveDistance = getDistance(start, end)

  const curTime = Date.now()
  // 获取挪动间隔时间   lastMoveTime:最初鼠标挪动工夫
  const moveTime = curTime - this.lastMoveTime
  // 计算速度
  const mouseSpeed = moveDistance / moveTime
  // 更新最初挪动工夫
  this.lastMoveTime = curTime
  return mouseSpeed
}

/**
 * 计算画笔宽度
 * @param speed 鼠标挪动速度
 */
_computedLineWidth(speed: number) {
  let lineWidth = 0
  const minWidth = this.minWidth
  const maxWidth = this.maxWidth
  if (speed >= this.maxSpeed) {lineWidth = minWidth} else if (speed <= this.minSpeed) {lineWidth = maxWidth} else {lineWidth = maxWidth - (speed / this.maxSpeed) * maxWidth
  }

  lineWidth = lineWidth * (1 / 3) + this.lastLineWidth * (2 / 3)
  this.lastLineWidth = lineWidth
  return lineWidth
}

渲染时就遍历所有坐标

/**
 * 自在画笔渲染
 * @param context canvas 二维渲染上下文
 * @param instance FreeDraw
 */
function freeDrawRender(
  context: CanvasRenderingContext2D,
  instance: FreeLine
) {context.save()
  context.lineCap = 'round'
  context.lineJoin = 'round'
  switch (instance.style) {
    // 当初是只有根底画笔,后续会减少不同的 case
    case FreeDrawStyle.Basic:
      context.strokeStyle = instance.colors[0]
      break
    default:
      break
  }
  for (let i = 1; i < instance.positions.length; i++) {switch (instance.style) {
      case FreeDrawStyle.Basic:
        _drawBasic(instance, i, context)
        break
      default:
        break
    }
  }
  context.restore()}

/**
 * 绘制根底线条
 * @param instance FreeDraw 实例
 * @param i 下标
 * @param context canvas 二维渲染上下文
 * @param cb 一些绘制前的解决,批改一些款式
 * 
 * 画笔轨迹是借鉴了网上的一些计划,分两种状况
 * 1. 如果是前两个坐标,就通过 lineTo 连贯即可
 * 2. 如果是前两个坐标之后的坐标,就采纳贝塞尔曲线进行连贯,*    比方当初有 a, b, c 三个点,到 c 点时,把 ab 坐标的两头点作为终点
 *       bc 坐标的两头点作为起点,b 点作为控制点进行连贯
 */
function _drawBasic(
  instance: FreeLine,
  i: number,
  context: CanvasRenderingContext2D
  cb?: (
    instance: FreeDraw,
    i: number,
    context: CanvasRenderingContext2D
  ) => void
) {const { positions, lineWidths} = instance
  const {x: centerX, y: centerY} = positions[i - 1]
  const {x: endX, y: endY} = positions[i]
  context.beginPath()
  if (i == 1) {context.moveTo(centerX, centerY)
    context.lineTo(endX, endY)
  } else {const { x: startX, y: startY} = positions[i - 2]
    const lastX = (startX + centerX) / 2
    const lastY = (startY + centerY) / 2
    const x = (centerX + endX) / 2
    const y = (centerY + endY) / 2
    context.moveTo(lastX, lastY)
    context.quadraticCurveTo(centerX, centerY, x, y)
  }

  context.lineWidth = lineWidths[i]
  cb?.(instance, i, context)
  context.stroke()}

荧光

荧光只需在根底款式上减少一个暗影即可

function freeDrawRender(
  context: CanvasRenderingContext2D,
  instance: FreeLine
) {context.save()
  context.lineCap = 'round'
  context.lineJoin = 'round'
  switch (instance.style) {
    // ...
    // 荧光 减少暗影成果
    case FreeDrawStyle.Shadow:
      context.shadowColor = instance.colors[0]
      context.strokeStyle = instance.colors[0]
      break
    default:
      break
  }
  for (let i = 1; i < instance.positions.length; i++) {switch (instance.style) {
      // ...
      // 荧光
      case FreeDrawStyle.Shadow:
        _drawBasic(instance, i, context, (instance, i, context) => {context.shadowBlur = instance.lineWidths[i]
        })
        break
      default:
        break
    }
  }
  context.restore()}

多色画笔

多色画笔须要应用context.createPattern,这个 api 是能够通过 canvas 创立一个指定的模版,而后能够让这个模版在指定的方向上反复元图像,具体应用能够看 MDN

/**
 * 自在画笔渲染
 * @param context canvas 二维渲染上下文
 * @param instance FreeDraw
 * @param material 画笔素材
 */
export const freeDrawRender = (
  context: CanvasRenderingContext2D,
  instance: FreeDraw,
  material: Material
) => {context.save()
  context.lineCap = 'round'
  context.lineJoin = 'round'
  switch (instance.style) {
    // ...
    // 多色画笔
    case FreeDrawStyle.MultiColor:
      context.strokeStyle = getMultiColorPattern(instance.colors)
      break
    default:
      break
  }

  for (let i = 1; i < instance.positions.length; i++) {switch (instance.style) {
      // ...
      // 多色画笔
      case FreeDrawStyle.MultiColor:
        _drawBasic(instance, i, context)
        break
      default:
        break
    }
  }
  context.restore()}

/**
 * 获取多色模版
 * @param colors 多色数组
 */
const getMultiColorPattern = (colors: string[]) => {const canvas = document.createElement('canvas')
  const context = canvas.getContext('2d') as CanvasRenderingContext2D
  const COLOR_WIDTH = 5 // 每个色彩的宽度

  canvas.width = COLOR_WIDTH * colors.length
  canvas.height = 20
  colors.forEach((color, i) => {
    context.fillStyle = color
    context.fillRect(COLOR_WIDTH * i, 0, COLOR_WIDTH, 20)
  })
  return context.createPattern(canvas, 'repeat') as CanvasPattern
}

喷雾

喷雾是一种相似雪花的成果,在鼠标挪动门路上随机绘制,然而最后我在写的时候发现,如果对每个点都进行随机雪花点记录而后缓存下来,内存占用过多,我就尝试了提前生成 5 套不同的数据,按程序展现,也能达到随机的成果

export const freeDrawRender = (
  context: CanvasRenderingContext2D,
  instance: FreeDraw,
  material: Material
) => {context.save()
  context.lineCap = 'round'
  context.lineJoin = 'round'
  switch (instance.style) {
    // ...
    // 喷雾
    case FreeDrawStyle.Spray:
      context.fillStyle = instance.colors[0]
      break
    default:
      break
  }

  for (let i = 1; i < instance.positions.length; i++) {switch (instance.style) {
      // ...
      // 喷雾
      case FreeDrawStyle.Spray:
        _drawSpray(instance, i, context)
        break
      default:
        break
    }
  }
  context.restore()}

/**
 * 绘制喷雾
 * @param instance FreeDraw 实例
 * @param i 下标
 * @param context canvas 二维渲染上下文
 */
const _drawSpray = (
  instance: FreeDraw,
  i: number,
  context: CanvasRenderingContext2D
) => {const { x, y} = instance.positions[i]
  for (let j = 0; j < 50; j++) {
    /**
     * sprayPoint 是我提前生成的 5 套随机喷雾数据,按程序展现
     * {
     *    angle 弧度
     *    radius 半径
     *    alpha 透明度
     * }
     */
    const {angle, radius, alpha} = sprayPoint[i % 5][j]
    context.globalAlpha = alpha
    const distanceX = radius * Math.cos(angle)
    const distanceY = radius * Math.sin(angle)
    // 依据宽度限度喷雾宽度,因为喷雾太细了不难看,我就对立放大一倍
    if (distanceX < instance.lineWidths[i] * 2 &&
      distanceY < instance.lineWidths[i] * 2 &&
      distanceX > -instance.lineWidths[i] * 2 &&
      distanceY > -instance.lineWidths[i] * 2
    ) {context.fillRect(x + distanceX, y + distanceY, 2, 2)
    }
  }
}

蜡笔

蜡笔成果也是应用了context.createPattern,首先我是以以后画笔色彩为底色,而后通过在网上找的一张蜡笔材质的透明图笼罩在下面,就能够实现蜡笔的成果

/**
 * 自在画笔渲染
 * @param context canvas 二维渲染上下文
 * @param instance FreeDraw
 * @param material 画笔素材
 */
export const freeDrawRender = (
  context: CanvasRenderingContext2D,
  instance: FreeDraw,
  material: Material
) => {context.save()
  context.lineCap = 'round'
  context.lineJoin = 'round'
  switch (instance.style) {
    // ...
    // 蜡笔
    case FreeDrawStyle.Crayon:
      context.strokeStyle = getCrayonPattern(instance.colors[0],
        material.crayon
      )
      break
    default:
      break
  }

  for (let i = 1; i < instance.positions.length; i++) {switch (instance.style) {
      // ...
      // 蜡笔
      case FreeDrawStyle.Crayon:
        _drawBasic(instance, i, context)
        break
      default:
        break
    }
  }
  context.restore()}

/**
 * 获取蜡笔模版
 * @param color 蜡笔底色
 * @param crayon 蜡笔素材
 */
const getCrayonPattern = (color: string, crayon: Material['crayon']) => {const canvas = document.createElement('canvas')
  const context = canvas.getContext('2d') as CanvasRenderingContext2D
  canvas.width = 100
  canvas.height = 100
  context.fillStyle = color
  context.fillRect(0, 0, 100, 100)
  if (crayon) {context.drawImage(crayon, 0, 0, 100, 100)
  }
  return context.createPattern(canvas, 'repeat') as CanvasPattern
}

泡泡

  1. 鼠标挪动时记录泡泡的半径和透明度
  2. 渲染时通过 context.arc 进行画圆绘制
addPosition(position: MousePosition) {
  // ...
  // 记录泡泡半径和透明度
  if (this.style === FreeDrawStyle.Bubble && this.bubbles) {
    this.bubbles.push({
      // getRandomInt 获取范畴内随机整数
      radius: getRandomInt(this.minWidth * 2, this.maxWidth * 2),
      // 透明度
      opacity: Math.random()})
  }
  // ...
}

/**
 * 绘制泡泡
 * @param instance FreeDraw 实例
 * @param i 下标
 * @param context canvas 二维渲染上下文
 */
const _drawBubble = (
  instance: FreeDraw,
  i: number,
  context: CanvasRenderingContext2D
) => {context.beginPath()
  if (instance.bubbles) {const { x, y} = instance.positions[i]
    context.globalAlpha = instance.bubbles[i].opacity
    context.arc(x, y, instance.bubbles[i].radius, 0, Math.PI * 2, false)
    context.fill()}
}

总结

如果有发现问题或者有好的计划,欢送探讨👻

画板系列文章:

  • 基于 canvas 实现的多功能画板
  • canvas 画板之绘画元素的框选

参考资料

  • Exploring canvas drawing techniques
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