在 firebase 云函数中创建方形缩略图

Question

我想在将图片上传到 firebase 中的云存储时创建一个方形缩略图。我只想将图像的中心裁剪成正方形，并将其调整为 150px x 150px。像这样：

上传时

我想要这个

上传时

我想要这个

我想在 Firebase 中这样做，但他们不只是使用 Imagemagick，而是使用 spawn，我无法弄清楚这两者如何结合在一起。

对于代码，我几乎只是从这里复制并粘贴了代码： https://github.com/firebase/functions-samples/blob/master/quickstarts/thumbnails/functions/index.js

我连图片的尺寸都获取不到，请问如何先获取尺寸，达到我想要的效果呢？

/**
 * Copyright 2016 Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for t`he specific language governing permissions and
 * limitations under the License.
 */
'use strict';

// [START import]
const functions = require('firebase-functions');
const gcs = require('@google-cloud/storage')();
const spawn = require('child-process-promise').spawn;
const path = require('path');
const os = require('os');
const fs = require('fs');
// [END import]

// [START generateThumbnail]
/**
 * When an image is uploaded in the Storage bucket We generate a thumbnail automatically using
 * ImageMagick.
 */
// [START generateThumbnailTrigger]
exports.generateThumbnail = functions.storage.object().onChange(event => {
// [END generateThumbnailTrigger]
  // [START eventAttributes]
  const object = event.data; // The Storage object.

  const fileBucket = object.bucket; // The Storage bucket that contains the file.
  const filePath = object.name; // File path in the bucket.
  const contentType = object.contentType; // File content type.
  const resourceState = object.resourceState; // The resourceState is 'exists' or 'not_exists' (for file/folder deletions).
  const metageneration = object.metageneration; // Number of times metadata has been generated. New objects have a value of 1.
  // [END eventAttributes]

  // [START stopConditions]
  // Exit if this is triggered on a file that is not an image.
  if (!contentType.startsWith('image/')) {
    console.log('This is not an image.');
    return;
  }

  // Get the file name.
  const fileName = path.basename(filePath);
  // Exit if the image is already a thumbnail.
  if (fileName.startsWith('thumb_')) {
    console.log('Already a Thumbnail.');
    return;
  }

  // Exit if this is a move or deletion event.
  if (resourceState === 'not_exists') {
    console.log('This is a deletion event.');
    return;
  }

  // Exit if file exists but is not new and is only being triggered
  // because of a metadata change.
  if (resourceState === 'exists' && metageneration > 1) {
    console.log('This is a metadata change event.');
    return;
  }
  // [END stopConditions]

  // [START thumbnailGeneration]
  // Download file from bucket.
  const bucket = gcs.bucket(fileBucket);
  const tempFilePath = path.join(os.tmpdir(), fileName);
  const metadata = { contentType: contentType };
  return bucket.file(filePath).download({
    destination: tempFilePath
  }).then(() => {
    console.log('Image downloaded locally to', tempFilePath);
    // Generate a thumbnail using ImageMagick.
    return spawn('convert', [tempFilePath, '-thumbnail', '200x200>', tempFilePath]);
  }).then(() => {
    console.log('Thumbnail created at', tempFilePath);
    // We add a 'thumb_' prefix to thumbnails file name. That's where we'll upload the thumbnail.
    const thumbFileName = `thumb_${fileName}`;
    const thumbFilePath = path.join(path.dirname(filePath), thumbFileName);
    // Uploading the thumbnail.
    return bucket.upload(tempFilePath, { destination: thumbFilePath, metadata: metadata });
  // Once the thumbnail has been uploaded delete the local file to free up disk space.
  }).then(() => fs.unlinkSync(tempFilePath));
  // [END thumbnailGeneration]
});
// [END generateThumbnail]

Answer 1

这是 imagemagick 代码行：

return spawn('convert', [tempFilePath, '-thumbnail', '200x200>', tempFilePath]);

它只是创建一个缩略图，尺寸末尾的 > 告诉它只缩小较大的文件但保持纵横比。您想在临时文件路径前添加 -gravity center -crop 200x200+0+0 。我不知道它是否像 , '-gravity', 'center', '-crop', '200x200+0+0'

一样简单

此外，您可能会遇到宽高比问题，但您可以在纵向和横向图像上尝试一下，看看会得到什么。

在 firebase 云函数中创建方形缩略图

Create square thumbnail in firebase cloud functions

imagemagick

child-process

node.js

google-cloud-functions