All Databases Inside Mac - Basic Toolbox

SetPortBits

SetPortBits Assigns a new bit map to the active GrafPort

#include <Quickdraw.h> Quickdraw

void SetPortBits(newBitMap );

BitMap *newBitMap ; pointer to a BitMap structure

SetPortBits replaces the portBits field of the active GrafPort with a new

value, effectively changing the entire contents of the port.

Returns: none

Notes: SetPortBits is useful for performing off-screen drawing. For instance,

you can use a series of Quickdraw calls to create an image in an off- screen

memory buffer, then use CopyBits to copy the bit-mapped image into the

normal screen.

Be sure that newBitMap is fully prepared before using this call; that is,

the memory for the bit-image has been allocated and the baseAddr,

rowBytes, and bounds fields have been set up.

Note that BitMap.rowBytes must be an even number and that it must be as

large or larger, in bits, than the width of the BitMap.bounds. The total

amount of memory needed for the off-screen bitMap is the product of the

height of the rectangle times the bytes-per-row. Here's a formula that

performs the calculation:

rectHigh = bounds.bottom - bounds.top;

rectWide = bounds.right - bounds.left;

rowBytes = ((rectWide -1) / 16) + 1) * 2;

buffSize = rowBytes * rectHigh; /* size in bytes */

The third line above correctly adjusts for the required word alignment.

Example

#include <Quickdraw.h>

#include <Memory.h>

OffScreenDraw( short rWide, short rHigh, Rect rDest )

// rWide, rHigh; size of off-screen rectangle

// rDest; on-screen destination */

{

BitMap saveBits;

BitMap tempBits;

short bytesPerRow;

saveBits = thePort->portBits; /* save current */

/* now create an off-screen "canvas" */

bytesPerRow = (( (rWide -1) / 16) + 1) * 2;

tempBits.baseAddr = (QDPtr)NewPtr( bytesPerRow * rHigh );

tempBits.rowBytes = bytesPerRow;

SetRect( &tempBits.bounds, 0,0, rWide, rHigh );

SetPortBits( &tempBits ); /* install the new BitMap */

EraseRect( & (thePort -> portBits.bounds) );/* clear out old material */

/* ... Draw some ovals, etc.; normally generate a complex figure ... */

SetPortBits( &saveBits ); /* restore the old BitMap */

/* copy temp map onto real map */

CopyBits( &tempBits, &saveBits, &tempBits.bounds, &rDest, srcOr, nil );

DisposPtr( (Ptr)tempBits.baseAddr );

}