Html5 Canvas实现图片标记、缩放、移动和保存历史状态功能 （附转换公式）

const handleLineMode = (downX: number, downY: number) => { // 省略一万字... canvas.onmouseup = () => { const imageData: ImageData = context.getImageData(0, 0, canvas.width, canvas.height) // 如果此时处于撤销状态，此时再使用画笔，则将之后的状态清空，以刚画的作为最新的画布状态 if (canvasCurrentHistory < canvasHistroyListRef.current.length) { canvasHistroyListRef.current = canvasHistroyListRef.current.slice(0, canvasCurrentHistory) } canvasHistroyListRef.current.push(imageData) setCanvasCurrentHistory(canvasCurrentHistory + 1) context.closePath() canvas.onmousemove = null canvas.onmouseup = null } }

画布状态的撤销与恢复

ok，其实现在关于画布状态的更新，我们已经完成了。接下来我们需要处理一下状态的撤销与恢复的功能啦

我们先定义一下这个工具栏吧

然后我们设置对应的事件，分别是撤销，恢复，与清空，其实都很容易看懂，最多就是处理一下边界情况。

const handleRollBack = () => { const isFirstHistory: boolean = canvasCurrentHistory === 1 if (isFirstHistory) return setCanvasCurrentHistory(canvasCurrentHistory - 1) } const handleRollForward = () => { const { current: canvasHistroyList } = canvasHistroyListRef const isLastHistory: boolean = canvasCurrentHistory === canvasHistroyList.length if (isLastHistory) return setCanvasCurrentHistory(canvasCurrentHistory + 1) } const handleClearCanvasClick = () => { const { current: canvas } = canvasRef const context: CanvasRenderingContext2D | undefined | null = canvas?.getContext('2d') if (!canvas || !context || canvasCurrentHistory === 0) return // 清空画布历史 canvasHistroyListRef.current = [canvasHistroyListRef.current[0]] setCanvasCurrentHistory(1) message.success('画布清除成功！') }

事件设置好之后，我们就可以开始监听一下这个 canvasCurrentHistory 当前状态下标，使用副作用函数进行处理

useEffect(() => { const { current: canvas } = canvasRef const { current: canvasHistroyList } = canvasHistroyListRef const context: CanvasRenderingContext2D | undefined | null = canvas?.getContext('2d') if (!canvas || !context || canvasCurrentHistory === 0) return context?.putImageData(canvasHistroyList[canvasCurrentHistory - 1], 0, 0) }, [canvasCurrentHistory])

为canvas画布填充图像信息！

这样就大功告成啦！！！

9. 实现鼠标图标的变化

我们简单的处理一下，画笔模式则是画笔的图标，橡皮擦模式下鼠标是橡皮擦，移动模式下就是普通的移动图标

切换模式时候，设置一下不同的图标

const handleMouseModeChange = (event: RadioChangeEvent) => { const { target: { value } } = event const { current: canvas } = canvasRef const { current: wrap } = wrapRef setmouseMode(value) if (!canvas || !wrap) return switch (value) { case MOVE_MODE: canvas.style.cursor = 'move' wrap.style.cursor = 'move' break case LINE_MODE: canvas.style.cursor = `url('http://cdn.algbb.cn/pencil.ico') 6 26, pointer` wrap.style.cursor = 'default' break case ERASER_MODE: message.warning('橡皮擦功能尚未完善，保存图片会出现错误') canvas.style.cursor = `url('http://cdn.algbb.cn/eraser.ico') 6 26, pointer` wrap.style.cursor = 'default' break default: canvas.style.cursor = 'default' wrap.style.cursor = 'default' break } }

10. 切换图片

现在的话只是一个demo状态，通过点击选择框，切换不同的图片

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