Technotes


PrGeneral Bug


Technote PR 08November 1987


Revised by: March 1988
Written by: Scott "ZZ" Zimmerman November 1987

This technical note documents a bug in the implementation of the PrGeneral procedure in the LaserWriter driver version 4.0. The bug has to do with the format of the information returned by the GetRslData opcode. This technical note will also describe a workaround for the problem.


One of the opcodes supported by the PrGeneral procedure (Technical Note #128) is named GetRslData. The GetRslData operation initializes a resolution record that is of the following form:

	TRslRg = RECORD {used in TGetRslBlk}
		iMin:	Integer;	{0 if printer only supports discrete resolutions}
		iMax:	Integer;	{0 if printer only supports discrete 
                                     resolutions}
	END;
						
	TRslRec = RECORD	{used in TGetRslBlk}
		iXRsl:	Integer;	{a discrete, physical X resolution}
		iYRsl:	Integer;	{a discrete, physical Y resolution}
	END;
	
	TGetRslBlk = RECORD {data block for GetRslData call}
		iOpCode:	Integer;	{input; = getRslDataOp}
		iError: 	Integer;	{output}
		lReserved:	LongInt;	{reserved for future use}
		iRgType:	Integer;	{output; this declaration is for RgType1}
		XRslRg: 	TRslRg; 	{output; range of X resolutions}
		YRslRg: 	TRslRg; 	{output; range of Y resolutions}
		iRslRecCnt: Integer;	{output; how many RslRecs follow}
		rgRslRec:	ARRAY[1..27] 
				OF TRslRec; {output; number used depends on printer type}
	END;

The LaserWriter 4.0 implementation has a bug that affects the YRslRg and XRslRg fields of the TGetRslBlk record. The correct values for the fields are:

		TGetRslBlk.XRslRg.iMin := 25;
		TGetRslBlk.XRslRg.iMax := 1500;
		TGetRslBlk.YRslRg.iMin := 25;
		TGetRslBlk.YRslRg.iMax := 1500;

Unfortunately, the information returned by the LaserWriter 4.0 version of PrGeneral is:

		TGetRslBlk.XRslRg.iMin := 25;
		TGetRslBlk.XRslRg.iMax := 25; 		TGetRslBlk.YRslRg.iMin := 1500;
		TGetRslBlk.YRslRg.iMax := 1500;

The recommended workaround for this problem is to use the PrDrvrVers function (Inside Macintosh II-163) to find out which version of the print driver you are using. If you are using 4.0, modify the resolution data before using it. The following code fragment illustrates this workaround:

	PROCEDURE CheckRslRecord(VAR theRslRecord: TGetRslBlk);
	CONST
		BogusDriver = 40;
	BEGIN
		IF PrDrvrVers = BogusDriver THEN BEGIN
			theRslRecord.XRslRg.iMax := theRslRecord.YRslRg.iMax;
			theRslRecord.YRslRg.iMin := theRslRecord.XRslRg.iMin;
		END;		
	END;

When the bug is fixed in a future version of the driver, the CheckRslRecord procedure will no longer have any effect on the resolution record. This will make sure your application gets the correct resolution data no matter which version of the driver is being used.

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