Reading images

read_png.mm

// Compile with:
// clang++ read_png.mm -framework ImageIO -framework CoreGraphics -framework CoreServices

#import <ImageIO/ImageIO.h>

int main() {
  const unsigned char png[] = {
      0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, 0x00, 0x00, 0x00, 0x0D,
      0x49, 0x48, 0x44, 0x52, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01,
      0x08, 0x06, 0x00, 0x00, 0x00, 0x1F, 0x15, 0xC4, 0x89, 0x00, 0x00, 0x00,
      0x0D, 0x49, 0x44, 0x41, 0x54, 0x08, 0x1D, 0x63, 0x10, 0xDF, 0xFE, 0x37,
      0x0F, 0x00, 0x04, 0xEE, 0x02, 0x3A, 0x01, 0x32, 0x70, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x49, 0x45, 0x4E, 0x44, 0xAE, 0x42, 0x60, 0x82};

  const size_t length = sizeof(png);

  CFDataRef data = CFDataCreateWithBytesNoCopy(kCFAllocatorDefault, png, length,
                                               kCFAllocatorNull);
  if (!data) {
    fprintf(stderr, "could not create CFDataRef\n");
    return 1;
  }

  CGImageSourceRef image_source = CGImageSourceCreateWithData(data, NULL);
  if (!image_source) {
    CFRelease(data);
    fprintf(stderr, "could not create CGImageSourceRef\n");
    return 1;
  }

  CGImageRef image = CGImageSourceCreateImageAtIndex(image_source, 0, NULL);
  if (!image) {
    CFRelease(image_source);
    CFRelease(data);
    fprintf(stderr, "could not create CGImageRef\n");
    return 1;
  }

  CGColorSpaceRef color_space = CGColorSpaceCreateDeviceRGB();
  if (!color_space) {
    CGImageRelease(image);
    CFRelease(image_source);
    CFRelease(data);
    fprintf(stderr, "could not create CGColorSpaceRef\n");
    return 1;
  }

  assert(CGImageGetWidth(image) == 1);
  assert(CGImageGetHeight(image) == 1);
  CGRect rect = {{0, 0}, {1, 1}};

  char img[4];

  CGContextRef context = CGBitmapContextCreate(img, 1, 1, 8, 1 * 4, color_space,
                                               kCGImageAlphaPremultipliedLast);
  if (!context) {
    CGColorSpaceRelease(color_space);
    CGImageRelease(image);
    CFRelease(image_source);
    CFRelease(data);
    fprintf(stderr, "could not create CGBitmapContext\n");
    return 1;
  }

  CGContextSetBlendMode(context, kCGBlendModeCopy);
  CGContextDrawImage(context, rect, image);

  CGContextRelease(context);
  CGColorSpaceRelease(color_space);
  CGImageRelease(image);
  CFRelease(image_source);
  CFRelease(data);

  fprintf(stderr, "expected r:% 4d g:% 4d b:% 4d a:% 4d\n", 23, 183, 252, 110);
  fprintf(stderr, "  actual r:% 4d g:% 4d b:% 4d a:% 4d\n", img[0], img[1], img[2], img[3]);
}