vImageAlphaBlend_NonpremultipliedToPremultiplied_ARGB8888(_:_:_:_:)
Composites a nonpremultiplied 8-bit-per-channel, ARGB buffer over a premultiplied ARGB buffer and generates a premultiplied result.
Declaration
func vImageAlphaBlend_NonpremultipliedToPremultiplied_ARGB8888(_ srcTop: UnsafePointer<vImage_Buffer>, _ srcBottom: UnsafePointer<vImage_Buffer>, _ dest: UnsafePointer<vImage_Buffer>, _ flags: vImage_Flags) -> vImage_ErrorParameters
- srcTop:
The vImage buffer that provides the nonpremultiplied source top image.
- srcBottom:
The vImage buffer that provides the premultiplied source bottom image.
- dest:
A pointer to the destination vImage buffer structure. You’re responsible for filling out the Height, Width, and Rowbytes fields of this structure, and for allocating a data buffer of the appropriate size. On return, the data buffer this structure points to contains the destination image data. When you no longer need the data buffer, deallocate the memory to prevent memory leaks.
- flags:
The options to use when performing the operation. If your code implements its own tiling or its own multithreading, pass Kvimagedonottile; otherwise, pass Kvimagenoflags.
Return Value
kvImageNoError; otherwise, one of the error codes in Data Types and Constants.
Discussion
On return of this function, the value of each pixel in the destination buffer is:
result = (srcTop * srctopAlpha + (255 - srcTopAlpha) * bottomAlpha + 127 ) / 255;