beginTransparencyLayer(auxiliaryInfo:)
Begins a transparency layer.
Declaration
func beginTransparencyLayer(auxiliaryInfo: CFDictionary?)Parameters
- auxiliaryInfo:
A dictionary that specifies any additional information, or
NULL.
Discussion
Until a corresponding call to endTransparencyLayer(), all subsequent drawing operations in the specified context are composited into a fully transparent backdrop (which is treated as a separate destination buffer from the context).
After a call to CGContextEndTransparencyLayer, the result is composited into the context using the global alpha and shadow state of the context. This operation respects the clipping region of the context.
After a call to this function, all of the parameters in the graphics state remain unchanged with the exception of the following:
The global alpha is set to
1.The shadow is turned off.
Ending the transparency layer restores these parameters to their previous values. Core Graphics maintains a transparency layer stack for each context, and transparency layers may be nested.