React 实现图片缩放

前言

用 React 实现图片缩放的功能。当拖动图片上四个角会沿着 x 轴放大和缩小图片。其中图片缩放的核心功能抽成 hook 来使用，需要把 hook 提供的 ref 设置到需要改变大小的节点的，当宽度改变时会改变 width 的 state 。

流程图

hook 代码

useImageResizer.tsx

import React, { useCallback, useEffect, useMemo, useRef, useState } from 'react';
import ReactDOM from 'react-dom';

// 改成一个期望的最小图片宽度常量
import { FLOAT_IMAGE_MINI_WIDTH } from 'src/constants/view';

import './image-resizer.less';

export enum ResizeDirection {
  LeftTop,
  LeftBottom,
  RightTop,
  RightBottom,
}

export interface ImageResizerProps {
  isActive: boolean;
  handleResizeStart?: (direction: ResizeDirection) => void;
  handleResizeEnd?: () => void;
}

export const useImageResizer = ({ isActive, handleResizeStart, handleResizeEnd }: ImageResizerProps) => {
  const [imageWith, setImageWidth] = useState(0);
  const [divElement] = useState<HTMLDivElement>(document.createElement('div'));
  const isDraggingRef = useRef(false);
  // 是否在拖动
  const [isDragging, setIsDragging] = useState(false);
  const imageContainerRef = useRef<HTMLDivElement>(null);

  const handleMouseMove = useCallback(
    (e: MouseEvent, resizeDirection: ResizeDirection, startX: number, imageWidth: number) => {
      // 计算移动距离
      const moveX = (e.clientX - startX) * 1;
      // 根据 resize 方向计算新的宽度
      let newWidth = imageWidth;
      switch (resizeDirection) {
        case ResizeDirection.LeftTop:
        case ResizeDirection.LeftBottom:
          newWidth -= moveX;
          break;
        case ResizeDirection.RightTop:
        case ResizeDirection.RightBottom:
          newWidth += moveX;
          break;
        default:
          break;
      }
      // 设置新的宽度
      setImageWidth(Math.max(newWidth, FLOAT_IMAGE_MINI_WIDTH));
    },
    []
  );

  const handleMouseDown = useCallback(
    (e: React.MouseEvent, resizeDirection: ResizeDirection) => {
      isDraggingRef.current = true;
      const startX = e.clientX;
      const imageWidth = imageContainerRef.current?.offsetWidth || 0;
      setIsDragging(true);
      handleResizeStart?.(resizeDirection);
      const handleMouseMoveFun = (e: MouseEvent) => {
        handleMouseMove(e, resizeDirection, startX, imageWidth);
      };
      const handleMouseUpFun = () => {
        isDraggingRef.current = false;
        setIsDragging(false);
        handleResizeEnd?.();
        // 移除监听
        window.removeEventListener('mousemove', handleMouseMoveFun);
        window.removeEventListener('mouseup', handleMouseUpFun);
      };
      window.addEventListener('mousemove', handleMouseMoveFun);
      window.addEventListener('mouseup', handleMouseUpFun);
    },
    [handleResizeStart, handleMouseMove, handleResizeEnd]
  );

  const Resizer = useMemo(
    () => (
      <>
        <div
          className="image-block__resizer-left-top"
          onMouseDown={e => handleMouseDown(e, ResizeDirection.LeftTop)}
        ></div>
        <div
          className="image-block__resizer-left-bottom"
          onMouseDown={e => handleMouseDown(e, ResizeDirection.LeftBottom)}
        ></div>
        <div
          className="image-block__resizer-right-top"
          onMouseDown={e => handleMouseDown(e, ResizeDirection.RightTop)}
        ></div>
        <div
          className="image-block__resizer-right-bottom"
          onMouseDown={e => handleMouseDown(e, ResizeDirection.RightBottom)}
        ></div>
      </>
    ),
    [handleMouseDown]
  );

  useEffect(() => {
    // 把 resizer 渲染到 divElement 上
    divElement.setAttribute('class', 'image-block__resizer');
    ReactDOM.render(Resizer, divElement);
    // 初始化 imageWidth
    setImageWidth(imageContainerRef.current?.offsetWidth || 0);
  }, [Resizer, divElement]);

  useEffect(() => {
    if (!isActive) {
      if (imageContainerRef.current?.contains(divElement)) {
        // 移除 imageContainerRef 上的 resizer
        imageContainerRef.current?.removeChild(divElement);
      }
    } else {
      setImageWidth(imageContainerRef.current?.offsetWidth || 0);
      // 往 imageContainerRef 上添加 resizer
      imageContainerRef.current?.appendChild(divElement);
    }
  }, [Resizer, divElement, imageContainerRef, isActive]);

  return { imageContainerRef, imageWith, isDraggingRef, isDragging };
};

image-resizer.less

.image-block__resizer {
  div {
    box-sizing: border-box;
    position: absolute;
    width: 12px;
    height: 12px;
    border: 2px solid rgb(255, 255, 255);
    box-shadow: rgba(0, 0, 0, .2) 0px 0px 4px;
    border-radius: 50%;
    z-index: 1;
    touch-action: none;
    background: rgb(30, 111, 255);
  }

  .image-block__resizer-left-top {
    left: 0px;
    top: 0px;
    margin-left: -6px;
    margin-top: -6px;
    cursor: nwse-resize;
  }

  .image-block__resizer-right-top {
    right: 0px;
    top: 0px;
    margin-right: -6px;
    margin-top: -6px;
    cursor: nesw-resize;
  }

  .image-block__resizer-right-bottom {
    right: 0px;
    bottom: 0px;
    margin-right: -6px;
    margin-bottom: -6px;
    cursor: nwse-resize;
  }

  .image-block__resizer-left-bottom {
    left: 0px;
    bottom: 0px;
    margin-left: -6px;
    margin-bottom: -6px;
    cursor: nesw-resize;
  }
}

.image-resize-dragging {
  cursor: move;
  user-select: none;
}

使用

index.tsx

因为图片缩放是在某个特定区域内进行的，所以会有图片最大宽高检测的逻辑，保证图片放大到特定宽度后不再放大。还增加了 delete 键的监听。 imagePosition 是图片对于固定原点的位置信息。

import React, { useState, useCallback, useRef, useMemo, CSSProperties, useEffect, KeyboardEvent } from 'react';

import { useImageResizer, ResizeDirection } from './useImageResizer';
import { PAGE_WIDTH } from 'src/constants/view';

import './index.less';

export interface FloatImage {
  image: string;
  width?: number;
  height?: number;
  top?: number;
  left?: number;
}

export interface FloatImagesProps {
  data: FloatImage[];
  pageHeight: number;
}

interface FloatImageBlockProps {
  data: FloatImage;
  pageHeight: number;
}

interface ImagePosition {
  top?: number;
  left?: number;
  bottom?: number;
  right?: number;
}

export const FloatImageBlock: React.FC<FloatImageBlockProps> = ({ data, pageHeight }) => {
  const { image, width, top = 0, left = 0 } = data;
  const [isActive, setIsActive] = useState(false);
  // 图片位置
  const [imagePosition, setImagePositionState] = useState<ImagePosition>({
    top,
    left,
  });
  const imagePositionRef = useRef<ImagePosition>(imagePosition);
  // 图片最大宽高
  const [imageMaxSize, setImageMaxSize] = useState<{ maxWidth?: number; maxHeight?: number }>({});
  const imageRef = useRef<HTMLImageElement>(null);

  const setImagePosition = useCallback((position: ImagePosition) => {
    setImagePositionState(position);
    imagePositionRef.current = position;
  }, []);

  const getImageInfo = useCallback(() => {
    const imageWidth = imageRef.current?.offsetWidth || 0;
    const imageHeight = imageRef.current?.offsetHeight || 0;
    return { imageWidth, imageHeight };
  }, []);

  const getPositionInfo = useCallback(
    ({ top, left, bottom = 0, right = 0 }: { top?: number; left?: number; bottom?: number; right?: number }) => {
      const { imageWidth, imageHeight } = getImageInfo();
      const newTop = top === undefined ? pageHeight - bottom - imageHeight : top;
      const newLeft = left === undefined ? PAGE_WIDTH - right - imageWidth : left;
      return { top: newTop, left: newLeft };
    },
    [getImageInfo, pageHeight]
  );

  const updateImageData = useCallback(() => {
    const { imageWidth, imageHeight } = getImageInfo();
    const { top, left, right = 0, bottom = 0 } = imagePositionRef.current;
    // 根据 imagePosition 和图片宽高获取最新的 top 和 left
    const newTop = top === undefined ? pageHeight - bottom - imageHeight : top;
    const newLeft = left === undefined ? PAGE_WIDTH - (right + imageWidth) : left;
    setImagePosition({ top: newTop, left: newLeft });
  }, [getImageInfo, pageHeight, setImagePosition]);

  const handleResizeStart = useCallback(
    (direction: ResizeDirection) => {
      // 根据 imagePosition 计算 top 和 left
      const { top: newTop, left: newLeft } = getPositionInfo(imagePositionRef.current);
      const { imageWidth, imageHeight } = getImageInfo();
      let maxWidth: number | undefined;
      let maxHeight: number | undefined;
      let newImagePosition: ImagePosition = {};
      // 根据 direction 设置 imagePosition
      switch (direction) {
        case ResizeDirection.LeftTop:
          newImagePosition = { bottom: pageHeight - newTop - imageHeight, right: PAGE_WIDTH - newLeft - imageWidth };
          maxWidth = imageWidth + newLeft;
          maxHeight = imageHeight + newTop;
          break;
        case ResizeDirection.LeftBottom:
          newImagePosition = { top: newTop, right: PAGE_WIDTH - newLeft - imageWidth };
          maxWidth = imageWidth + newLeft;
          maxHeight = pageHeight - newTop;
          break;
        case ResizeDirection.RightTop:
          newImagePosition = { bottom: pageHeight - newTop - imageHeight, left: newLeft };
          maxWidth = PAGE_WIDTH - newLeft;
          maxHeight = imageHeight + newTop;
          break;
        case ResizeDirection.RightBottom:
          newImagePosition = { top: newTop, left: newLeft };
          maxWidth = PAGE_WIDTH - newLeft;
          maxHeight = pageHeight - newTop;
          break;
        default:
          break;
      }
      if (maxWidth === undefined || maxHeight === undefined) {
        return;
      }
      setImagePosition(newImagePosition);
      // 按照图片宽高比计算最大宽高
      maxWidth = Math.min((maxHeight / imageHeight) * imageWidth, maxWidth);
      maxHeight = Math.min(pageHeight, (maxWidth / imageWidth) * imageHeight);
      if (maxWidth < maxHeight) {
        setImageMaxSize({ maxWidth, maxHeight: maxWidth * (imageHeight / imageWidth) });
      } else {
        setImageMaxSize({ maxHeight, maxWidth: maxHeight * (imageWidth / imageHeight) });
      }
    },
    [getImageInfo, getPositionInfo, pageHeight, setImagePosition]
  );

  const handleResizeEnd = useMemo(
    () =>
      // 设置 active 为 true
      () => {
        const timer = setTimeout(() => {
          setIsActive(true);
          updateImageData();
          clearTimeout(timer);
        }, 0);
      },
    [updateImageData]
  );

  const {
    imageContainerRef,
    imageWith,
    isDragging,
  } = useImageResizer({ isActive, handleResizeStart, handleResizeEnd });

  const handleClick = useCallback(() => {
    setIsActive(true);
  }, []);

  const style = useMemo(
    (): CSSProperties => ({
      position: 'absolute',
      zIndex: isActive ? 101 : 100,
      ...imagePosition,
    }),
    [imagePosition, isActive]
  );

  // 增加 delete 事件
  const deleteHandler = (e: KeyboardEvent<HTMLDivElement>) => {
    if (isActive && (e.key === 'Backspace' || e.key === 'Delete')) {
      // 删除图片
    }
  };

  useEffect(() => {
    const handler = (e: MouseEvent) => {
      // 点击的区域不在图片上
      if (!imageContainerRef.current?.contains(e.target as Node)) {
        setIsActive(false);
      }
    };

    window.addEventListener('mousedown', handler);
    return () => {
      window.removeEventListener('mousedown', handler);
    };
  }, [isActive, imageContainerRef]);

  return (
    <>
      {(
        <div
          className={'image-block-container'}
          style={style}
          onClick={handleClick}
          onKeyDown={deleteHandler}
          tabIndex={0}
        >
          <div ref={imageContainerRef} className="image-block">
            <img
              ref={imageRef}
              src={image}
              style={{ width: `${imageWith || width}px`, ...imageMaxSize }}
              alt=""
            />
            <div
              className={`image-block-mask ${isActive ? 'image-block-mask-active' : ''} ${isDragging ? 'image-block-mask-dragging' : ''
                }`}
            ></div>
          </div>
        </div>
      )}
    </>
  );
};

index.less

.image-block-container {
  display: flex;
  justify-content: center;
  align-items: center;

  .image-block {
    position: relative;
    display: flex;
    user-select: none;
    max-width: 100%;
    max-height: 100%;

    img {
      max-width: 100%;
      max-height: 100%;
    }

    .image-block-mask {
      position: absolute;
      height: 100%;
      width: 100%;
      top: 0;
      left: 0;
    }

    .image-block-mask-active {
      background: rgba(30, 111, 255, .12);
      cursor: move;
    }

    .image-block-mask-dragging::before {
      content: '';
      width: 10000px;
      height: 10000px;
      position: absolute;
      top: -5000px;
      left: -5000px;
      cursor: move;
    }
  }
}