CGContextSaveGState

CGContextSaveGState is a function in Core Graphics that pushes a copy of the current graphics state onto the graphics state stack for a given graphics context. The graphics state is a collection of settings that affect drawing operations, and saving it allows a program to temporarily modify these settings and later restore them to their previous values. The save operation is per-context, so each CGContext has its own stack.

A graphics state typically includes transformation information (the current transformation matrix), the clipping path, alpha and compositing settings, dash patterns and other line styles, color and pattern information, color space, and other drawing parameters such as stroke and fill attributes. When you call the save function, all of these elements are preserved on the stack, so changes you make after saving can be undone by restoring the previous state.

Common usage patterns involve saving the state before applying a local change, performing drawing with the altered state, and then restoring the state to continue drawing with the original settings. This is especially useful when applying temporary transforms, clipping regions, or color and line style changes for a specific drawing operation.

In Swift, the equivalent calls are context.saveGState() and context.restoreGState(), while in Objective-C they are CGContextSaveGState(context) and CGContextRestoreGState(context). It is important to balance each save with a corresponding restore to avoid leaving the graphics state altered and to maintain predictable rendering.