kmpdfkit_demo/PDFViewer/Source/PDFBackground/PDFBackgroundDrawImageView.m

//
//  CPDFDrawImageView.m
//  PDFViewer
//
//  Created by kdanmobile_2 on 2023/1/3.
//

#import "PDFBackgroundDrawImageView.h"

@implementation PDFBackgroundDrawImageView

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    
    if (self) {
        self.backgroundColor = [UIColor clearColor];
    }
    
    return self;
}

- (void)drawRect:(CGRect)rect {
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    [self showDraw:context];
}

- (void)showDraw:(CGContextRef)context {
    UIImage *newImage = [self imageToTransparent:_image];
    
    [newImage drawInRect:self.bounds blendMode:kCGBlendModeNormal alpha:1.0f];
}

- (UIImage*) imageToTransparent:(UIImage*) image {
    const int imageWidth = image.size.width;
    const int imageHeight = image.size.height;
    size_t bytesPerRow = imageWidth * 4;
    uint32_t *rgbImageBuf = (uint32_t *)malloc(bytesPerRow * imageHeight);
    
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(rgbImageBuf, imageWidth, imageHeight, 8, bytesPerRow, colorSpace
                                                 , kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
    
    CGContextDrawImage(context, CGRectMake(0, 0, imageWidth, imageHeight), image.CGImage);
    
    int pixelNum = imageWidth * imageHeight;
    uint32_t* pCurPtr = rgbImageBuf;
    for (int i = 0; i < pixelNum; i++, pCurPtr++)
    {
        if ((*pCurPtr & 0x65815A00) == 0x65815a00)
        {
            uint8_t* ptr = (uint8_t*)pCurPtr;
            ptr[0] = 0;
        }
    }

    CGDataProviderRef dataProvider =CGDataProviderCreateWithData(NULL, rgbImageBuf, bytesPerRow * imageHeight, ProviderReleaseData);
    CGImageRef imageRef = CGImageCreate(imageWidth, imageHeight,8, 32, bytesPerRow, colorSpace,
                                        kCGImageAlphaLast |kCGBitmapByteOrder32Little, dataProvider,
                                        NULL, true,kCGRenderingIntentDefault);
    CGDataProviderRelease(dataProvider);

    UIImage* resultUIImage = [UIImage imageWithCGImage:imageRef];

    CGImageRelease(imageRef);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    return resultUIImage;
}

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

@end