Legacy Document

Inside Macintosh: Imaging With QuickDraw /

Chapter 6 - Offscreen Graphics Worlds / Offscreen Graphics Worlds Reference

Routines / Creating, Altering, and Disposing of Offscreen Graphics Worlds

NewScreenBuffer

The NewGWorld function uses the NewScreenBuffer function to create an offscreen PixMap record and allocate memory for the base address of its pixel image; applications generally don't need to use NewScreenBuffer.

FUNCTION NewScreenBuffer (globalRect: Rect; 
                          purgeable: Boolean; VAR gdh: GDHandle; 
                          VAR offscreenPixMap: PixMapHandle): 
                          QDErr;

globalRect

The boundary rectangle, in global coordinates, for the offscreen pixel map.

purgeable

A value of TRUE to make the memory block for the offscreen pixel map purgeable, or a value of FALSE to make it unpurgeable.

gdh

The handle to the GDevice record for the graphics device with the greatest pixel depth among all graphics devices whose boundary rectangles intersect the rectangle specified in the globalRect parameter.

offscreenPixMap

A handle to the new offscreen PixMap record.

DESCRIPTION

The NewScreenBuffer function creates a new offscreen PixMap record, using the pixel depth and color table of the device whose GDevice record is returned in the gdh parameter. The NewScreenBuffer function returns a handle to the new offscreen pixel map in the offscreenPixMap parameter.

As its function result, NewScreenBuffer returns one of three result codes.

SPECIAL CONSIDERATIONS

The NewScreenBuffer function may move or purge memory blocks in the application heap. Your application should not call this function at interrupt time.

ASSEMBLY-LANGUAGE INFORMATION

The trap macro and routine selector for the NewScreenBuffer function are

Trap macro	Selector
_QDExtensions	$000E0010

RESULT CODES

noErr	0	No error
paramErr	-50	Illegal parameter
cNoMemErr	-152	Failed to allocate memory for structures