Now that we have scanners and other massive-picture producing types of applications, there is a need to address the problem of how to display a PICT format object that is bigger than a current PICT resource is allowed to be. Note that this technique applies equally well to version 1 and version 2
(word-opcode) pictures as produced by the Macintosh II.
Think of the handle returned by a GetResource('PICT',ID) as a ΓÇ£handleΓÇ¥ in the more general sense of being an abstract ΓÇ£tagΓÇ¥ΓÇösomething that the ROM routines can use to draw the picture with. DonΓÇÖt assume that the entire picture has been read into memory or that you can directly read any bytes beyond the basic Picture record structure (picSize followed by picFrame). Someday we may provide a mechanism for the resource to be disk- instead of memory-based. The QuickDraw bottleneck procedures will know how to get data from and put data into the pictures in any case.
Spooling from a PICT file
In order to display pictures of arbitrary size, your application should be able to import a QuickDraw picture from a file of type PICT. This is the file produced by a “Save as…” from MacDraw with the PICT option selected.
What follows is a small program fragment that demonstrates how to spool in a picture from [the data fork of] a PICT file. The picture can be larger than the historical 32K resource size. See technical note #88 if you are unfamiliar with the Signal mechanism. We assume that a CatchSignals has been done before GetandDrawPICTFile is called.
MPW Pascal Example
{the following variable must be at the top level}
VAR
globalRef : INTEGER; {refNum of the file to read from}
{the following procedure must be at the top level}
DrawPicture(myPicture,&(**myPicture).picFrame); /*draw the picture*/
err = GetFPos(globalRef,&filePos);/*get position for check*/
if (err != noErr) return err;
err = FSClose(globalRef);
if (err != noErr) return err;
DisposHandle((Handle)myPicture);
(*qd.thePort).grafProcs = savedProcs;/*restore the procs*/
/*Check for errors. if there wasn't enough room,*/
/*DrawPicture will abort; the FILE position mark*/
/*won't be at the end of the FILE.*/
if (filePos != myEOF) return abortPICT;
else return noErr;
} /*if (reply.good) */
} /* GetDrawPICTFile */
More on Picture Compatibility
Many applications already support PICT resources larger than 32K. The 128K ROMs (and later) allow pictures as large as memory (or spooling) will accommodate. This was made possible by having QuickDraw ignore the size word and simply read the picture until the end-of-picture opcode was reached.
For maximum safety and convenience, let QuickDraw generate and interpret your pictures.
While Apple has provided you with the data formats that allow you to read or write picture data directly, we recommend that you always let DrawPicture or OpenPicture and ClosePicture process the opcodes.
One reason to read a picture directly by scanning the opcodes would be to disassemble it to, for example, extract a Color QuickDraw pixel map to save off in a private data structure. This shouldnΓÇÖt normally be necessary.
If you do look at the picture data be sure and check the version information. You may want to put up an alert in your application that indicates to the user when a picture was created using a later version of the picture format than your application recognizes, letting them know that some elements of the picture cannot be displayed. If the version information indicates a QuickDraw picture version later than the one recognized by your application, your program should skip over the new opcodes and only attempt to parse the ones it knows.
As with reading picture data directly, it is best to use QuickDraw to create data in the PICT format. If you do need to create PICT format data directly, it is essential that you use the latest opcode specifications and that you thoroughly test the data produced on both color and black and white Macintosh machines. Contact Macintosh Developer Technical Support if you are not sure that you have the latest specifications.
Apple does not guarantee that a picture which wasnΓÇÖt produced by QuickDraw will work.
