Swift版本

步骤：

1. 下载 WebpFramework-1.0.0
2. 仅导入decoder
3. 在swift项目中，随便创建objc文件，以便自动生成桥接用的头文件，删除无用的.m文件
4. 在XXX-Bridging-Header.h 中，写入#import <WebPDecoder/decode.h>
5. 添加UIImage+Webp.swift，代码如下

//
//  UIImage+Webp.swift
//  FileShare
//
//  Created by JadianZheng on 2018/7/26.
//  Copyright © 2018 JadianZheng. All rights reserved.
//

import UIKit

private func freeWebPData(info: UnsafeMutableRawPointer?, data: UnsafeRawPointer, size: Int) -> Void {
    free(UnsafeMutableRawPointer(mutating: data))
}

extension UIImage {
    convenience init?(webPPath path: String) {
        guard let imageData = NSData(contentsOfFile: path) else {
            return nil
        }
        
        var width: CInt = 0
        var height: CInt = 0
        let rgbaData = WebPDecodeRGBA(imageData.bytes.assumingMemoryBound(to: UInt8.self), imageData.length, &width, &height)
        
        let provider = CGDataProvider(dataInfo: nil, data: rgbaData!, size: Int(width) * Int(height) * 4, releaseData: freeWebPData)
        let bitmapWithAlpha = CGBitmapInfo(rawValue: CGImageAlphaInfo.last.rawValue)
        
        if let cgimage = CGImage(width:Int(width),
                                 height:Int(height),
                                 bitsPerComponent: 8,
                                 bitsPerPixel: 32,
                                 bytesPerRow: 4 * Int(width),
                                 space: CGColorSpaceCreateDeviceRGB(),
                                 bitmapInfo: bitmapWithAlpha,
                                 provider: provider!,
                                 decode: nil,
                                 shouldInterpolate: true,
                                 intent: CGColorRenderingIntent.defaultIntent) {
            self.init(cgImage: cgimage)
        }
        else {
            return nil
        }
    }
}

Object-C 版本

步骤：

1. 下载 WebpFramework-1.0.0
2. 仅导入decoder
3. 添加UIImage类别，如下：

//
//  UIImage+WebP.h
//  Webp
//
//  Created by JadianZheng on 2018/8/2.
//  Copyright © 2018 JadianZheng. All rights reserved.
//

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface UIImage (WebP)

+ (UIImage*)imageWithWebp:(NSURL*)fileURL;

@end

NS_ASSUME_NONNULL_END

//
//  UIImage+WebP.m
//  Webp
//
//  Created by JadianZheng on 2018/8/2.
//  Copyright © 2018 JadianZheng. All rights reserved.
//

#import "UIImage+WebP.h"
#import <WebPDecoder/decode.h>

@implementation UIImage (WebP)

static void free_image_data(void *info, const void *data, size_t size) {
    free((void*) data);
}

+ (UIImage*)imageWithWebp:(NSURL*)fileURL {
    NSData *imageData = [NSData dataWithContentsOfURL:fileURL];
    
    int width = 0, height = 0;
    uint8_t* data = WebPDecodeRGBA(imageData.bytes, imageData.length, &width, &height);
    
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, data, width * 4 * height, free_image_data);
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    
    CGImageRef imageRef = CGImageCreate(width, height, 8, 32, 4 * width,
                                        colorSpaceRef, kCGBitmapByteOrderDefault, provider, NULL, NO, kCGRenderingIntentDefault);
    UIImage *result = [UIImage imageWithCGImage:imageRef];
    
    CGImageRelease(imageRef);
    CGColorSpaceRelease(colorSpaceRef);
    CGDataProviderRelease(provider);
    
    return result;
}

@end