Mac OS For QuickTime Programmers

QuickDraw Operations Offscreen

When using QuickDraw with QuickTime, you may want to work offscreen. "Offscreen Graphics Worlds," describes the following functions and data structures that QuickTime 3 programmers can access:

NewGWorld creates an offscreen graphics world. It uses NewScreenBuffer and NewTempScreenBuffer to create an offscreen PixMap record and allocate memory for the base address of its pixel image. It returns a pointer of type GWorldPtr by which your application refers to the offscreen graphics world. These types are described in "Data Structures" .
UpdateGWorld changes the pixel depth, boundary rectangle, or color table for an existing offscreen graphics world.
DisposeGWorld uses DisposeScreenBuffer to dispose of all the memory allocated for an offscreen graphics world.
GetGWorld gets the current graphics port (color graphics port or offscreen graphics world) and the current GDevice record (see "Creating, Setting, and Disposing of GDevice Records" ).
SetGWorld changes the current graphics port (color graphics port or offscreen graphics world).
GetGWorldDevice obtains a handle to the Graphic Device record associated with an offscreen graphics world.
GetGWorldPixMap obtains the pixel map previously created for an offscreen graphics world.
LockPixels prevents the base address of an offscreen pixel image from being moved while you draw into or copy from its pixel map.
UnlockPixels frees the base address of an offscreen pixel image when you have finished drawing into or copying from an offscreen graphics world.
GetPixelsState saves current information about the memory allocated for an offscreen pixel image.
SetPixelsState restores an offscreen pixel image to the state previously saved by GetPixelsState .
GetPixBaseAddr obtains a pointer to an offscreen pixel map.

Several of the routines listed above expect or return values defined by the GWorldFlags data type, which specify a number of options for offscreen graphics worlds. It is described in "Data Structures" .