react-native/Libraries/Image/RCTImageBlurUtils.m

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

#import "RCTImageBlurUtils.h"

UIImage *RCTBlurredImageWithRadius(UIImage *inputImage, CGFloat radius)
{
  CGImageRef imageRef = inputImage.CGImage;
  CGFloat imageScale = inputImage.scale;
  UIImageOrientation imageOrientation = inputImage.imageOrientation;

  // Image must be nonzero size
  if (CGImageGetWidth(imageRef) * CGImageGetHeight(imageRef) == 0) {
    return inputImage;
  }

  //convert to ARGB if it isn't
  if (CGImageGetBitsPerPixel(imageRef) != 32 ||
      CGImageGetBitsPerComponent(imageRef) != 8 ||
      !((CGImageGetBitmapInfo(imageRef) & kCGBitmapAlphaInfoMask))) {
    UIGraphicsBeginImageContextWithOptions(inputImage.size, NO, inputImage.scale);
    [inputImage drawAtPoint:CGPointZero];
    imageRef = UIGraphicsGetImageFromCurrentImageContext().CGImage;
    UIGraphicsEndImageContext();
  }

  vImage_Buffer buffer1, buffer2;
  buffer1.width = buffer2.width = CGImageGetWidth(imageRef);
  buffer1.height = buffer2.height = CGImageGetHeight(imageRef);
  buffer1.rowBytes = buffer2.rowBytes = CGImageGetBytesPerRow(imageRef);
  size_t bytes = buffer1.rowBytes * buffer1.height;
  buffer1.data = malloc(bytes);
  buffer2.data = malloc(bytes);
  if (!buffer1.data || !buffer2.data) {
    // CWE - 391 : Unchecked error condition
    // https://www.cvedetails.com/cwe-details/391/Unchecked-Error-Condition.html
    // https://eli.thegreenplace.net/2009/10/30/handling-out-of-memory-conditions-in-c
    abort();
  }

  // A description of how to compute the box kernel width from the Gaussian
  // radius (aka standard deviation) appears in the SVG spec:
  // http://www.w3.org/TR/SVG/filters.html#feGaussianBlurElement
  uint32_t boxSize = floor((radius * imageScale * 3 * sqrt(2 * M_PI) / 4 + 0.5) / 2);
  boxSize |= 1; // Ensure boxSize is odd

  //create temp buffer
  void *tempBuffer = malloc((size_t)vImageBoxConvolve_ARGB8888(&buffer1, &buffer2, NULL, 0, 0, boxSize, boxSize,
                                                               NULL, kvImageEdgeExtend + kvImageGetTempBufferSize));
  if (!tempBuffer) {
    // CWE - 391 : Unchecked error condition
    // https://www.cvedetails.com/cwe-details/391/Unchecked-Error-Condition.html
    // https://eli.thegreenplace.net/2009/10/30/handling-out-of-memory-conditions-in-c
    abort();
  }

  //copy image data
  CFDataRef dataSource = CGDataProviderCopyData(CGImageGetDataProvider(imageRef));
  memcpy(buffer1.data, CFDataGetBytePtr(dataSource), bytes);
  CFRelease(dataSource);

  //perform blur
  vImageBoxConvolve_ARGB8888(&buffer1, &buffer2, tempBuffer, 0, 0, boxSize, boxSize, NULL, kvImageEdgeExtend);
  vImageBoxConvolve_ARGB8888(&buffer2, &buffer1, tempBuffer, 0, 0, boxSize, boxSize, NULL, kvImageEdgeExtend);
  vImageBoxConvolve_ARGB8888(&buffer1, &buffer2, tempBuffer, 0, 0, boxSize, boxSize, NULL, kvImageEdgeExtend);

  //free buffers
  free(buffer2.data);
  free(tempBuffer);

  //create image context from buffer
  CGContextRef ctx = CGBitmapContextCreate(buffer1.data, buffer1.width, buffer1.height,
                                           8, buffer1.rowBytes, CGImageGetColorSpace(imageRef),
                                           CGImageGetBitmapInfo(imageRef));

  //create image from context
  imageRef = CGBitmapContextCreateImage(ctx);
  UIImage *outputImage = [UIImage imageWithCGImage:imageRef scale:imageScale orientation:imageOrientation];
  CGImageRelease(imageRef);
  CGContextRelease(ctx);
  free(buffer1.data);
  return outputImage;
}