CGBitmapContextCreate

CGBitmapContextCreate is a Core Graphics function that creates a bitmap-based graphics context backed by a memory buffer. It is part of Quartz 2D and is commonly used for offscreen drawing, image generation, and pixel-level rendering.

The function signature is CGContextRef CGBitmapContextCreate(void *data, size_t width, size_t height, size_t bitsPerComponent, size_t bytesPerRow, CGColorSpaceRef colorspace, CGBitmapInfo bitmapInfo). The data parameter points to memory that will back the bitmap; if data is NULL, Core Graphics allocates a buffer. Width and height specify the pixel dimensions of the context. bitsPerComponent is the number of bits used for each color component (typical value is 8). bytesPerRow indicates the length of a row in bytes; passing 0 lets the system compute an appropriate value. colorspace selects the color space (commonly a device RGB color space). bitmapInfo encodes alpha handling and byte order, such as premultiplied alpha and the order of color components.

The created context can be used like any other Core Graphics drawing destination. After drawing, you can obtain a CGImage via CGBitmapContextCreateImage or access the raw pixel data with CGBitmapContextGetData. The context must be released when finished with CGContextRelease. If you supplied an external data buffer, you are responsible for its memory; if data was NULL, the system typically manages the backing buffer as part of the context.

In Swift, the same functionality is exposed through higher-level CGContext initializers that bridge to CGBitmapContextCreate, providing a more Swift-friendly API while preserving the underlying behavior.