从CFData读取像素字节：对指向不完整类型的指针进行算术运算

Question

此代码应该从CGImageRef：

开始获取每个像素的值

UIImage* image = [UIImage imageNamed:@"mask.bmp"];
CGImageRef aCGImageRef = image.CGImage;

CFDataRef rawData = CGDataProviderCopyData(CGImageGetDataProvider(aCGImageRef));
UInt8 * buf = (UInt8 *) CFDataGetBytePtr(rawData);
int length = CFDataGetLength(rawData);

CFRelease(rawData);

int no_of_channels = 3;
int image_width = SCREEN_WIDTH();

unsigned long row_stride = image_width * no_of_channels; // 960 bytes in this case
unsigned long x_offset = x * no_of_channels;

/* assuming RGB byte order (as opposed to BGR) */
UInt8 r = *(rawData + row_stride * y + x_offset );
UInt8 g = *(rawData + row_stride * y + x_offset + 1);
UInt8 b = *(rawData + row_stride * y + x_offset + 2);

最后三行可以解决这个问题，但是编译器表示不会将x和y用作float。所以我将它们投放到int，但现在它说了

  

指向不完整类型const结构的指针__CFData

我该如何解决？

Answer 1

您希望对字节指针本身进行算术运算，而不是对CFData结构（将字节作为成员）进行算术运算。这意味着使用上面的buf变量：

UInt8 r = *(buf + row_stride * y + x_offset );
UInt8 g = *(buf + row_stride * y + x_offset + 1);
UInt8 b = *(buf + row_stride * y + x_offset + 2);