HTML5 Canvas 图像灰度滤镜教程

要对 Konva.Image 应用滤镜，必须先使用 cache() 函数缓存它。然后使用 filters() 函数应用滤镜。

要使用 Konva 反转图像颜色，可以使用 Konva.Filters.Grayscale 滤镜。

有关全部可用滤镜，请参阅 滤镜文档。

Vanilla

import Konva from 'konva';

const stage = new Konva.Stage({
  container: 'container',
  width: window.innerWidth,
  height: window.innerHeight,
});

const layer = new Konva.Layer();
stage.add(layer);

const imageObj = new Image();
imageObj.onload = () => {
  const image = new Konva.Image({
    x: 50,
    y: 50,
    image: imageObj,
    draggable: true,
  });

  layer.add(image);

  image.cache();
  image.filters([Konva.Filters.Grayscale]);
};
imageObj.src = 'https://konvajs.org/assets/darth-vader.jpg';
imageObj.crossOrigin = 'anonymous';

React

import Konva from 'konva';
import { Stage, Layer, Image } from 'react-konva';
import { useState, useEffect, useRef } from 'react';
import useImage from 'use-image';

const App = () => {
  const [position, setPosition] = useState({ x: 50, y: 50 });
  const [image] = useImage('https://konvajs.org/assets/darth-vader.jpg', 'anonymous');
  const imageRef = useRef(null);

  useEffect(() => {
    if (image) {
      imageRef.current.cache();
    }
  }, [image]);

  return (
    <Stage width={window.innerWidth} height={window.innerHeight}>
      <Layer>
        {image && (
          <Image
            ref={imageRef}
            x={position.x}
            y={position.y}
            image={image}
            draggable
            onDragEnd={(e) => {
              setPosition({ x: e.target.x(), y: e.target.y() });
            }}
            filters={[Konva.Filters.Grayscale]}
          />
        )}
      </Layer>
    </Stage>
  );
};

export default App;

Vue

<template>
  <v-stage :config="stageSize">
    <v-layer>
      <v-image
        ref="imageNode"
        :config="{
          x: 50,
          y: 50,
          image: image,
          draggable: true,
          filters: [Konva.Filters.Grayscale],
        }"
      />
    </v-layer>
  </v-stage>
</template>

<script setup>
import { ref, watch, nextTick } from 'vue';
import { useImage } from 'vue-konva';
import Konva from 'konva';

const stageSize = {
  width: window.innerWidth,
  height: window.innerHeight,
};

const imageNode = ref(null);
const [image] = useImage('https://konvajs.org/assets/darth-vader.jpg', 'anonymous');

watch(image, async (newImage) => {
  if (newImage) {
    await nextTick();
    imageNode.value.getNode().cache();
  }
});
</script>