vImagePremultipliedConstAlphaBlend_Planar8(_:_:_:_:_:_:)
Performs premultiplied alpha compositing of two 8-bit planar buffers and applies an extra alpha value to the top buffer.
Declaration
func vImagePremultipliedConstAlphaBlend_Planar8(_ srcTop: UnsafePointer<vImage_Buffer>, _ constAlpha: Pixel_8, _ srcTopAlpha: UnsafePointer<vImage_Buffer>, _ srcBottom: UnsafePointer<vImage_Buffer>, _ dest: UnsafePointer<vImage_Buffer>, _ flags: vImage_Flags) -> vImage_ErrorParameters
- srcTop:
The vImage buffer that provides the source top image.
- constAlpha:
The constant alpha value that the function applies to the top image.
- srcTopAlpha:
The vImage buffer that provides the source top alpha.
- srcBottom:
The vImage buffer that provides the 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:
uint8_t destColor = (srcTopColor * constAlpha * 255 + (255*255 - srcTopAlpha * constAlpha) * srcBottomColor + 127*255) / (255*255);