GXBufferData(IM:XP)

Inside Macintosh: QuickDraw GX Printing Extensions and Drivers /

Chapter 4 - Printing Messages / Printing Messages Reference

Printing Messages / Device Communications Messages

GXBufferData
QuickDraw GX sends the GXBufferData message to send data to the device using the standard buffering mechanism. You can override the GXBufferData message to provide your own buffering scheme or to change data prior to buffering. Your override of the GXBufferData message must match the following formal declaration:
OSErr MyBufferData (Ptr data, long length, long bufferOptions);
data
A pointer to the data to add to the buffer.
length
The number of bytes of data to add.
bufferOptions
Options for adding the data to the buffer, as shown in Table 4-10.

function result
An error code. The value noErr indicates that the operation was successful.

DESCRIPTION
QuickDraw GX sends the GXBufferData message in preparation for sending data to
a device using the standard buffering mechanism. This message is sent whenever any message handler wishes to buffer the data to be sent to the printing device.
The default implementation of this message uses the default buffering. It buffers the data until all of the buffers are full. You can specify buffering options in the bufferOptions parameter. The constants for these options are shown in Table 4-10.
Table 4-10 Options for adding data to the buffer
Constant Value Explanation
gxNoBufferOptions 0x00000000 No options apply.
gxMakeBufferHex 0x00000001 All data is converted into ASCII hex equivalents: each byte becomes 2 ASCII bytes.
gxDontSplitBuffer 0x00000002 The data sent in this message cannot be split across buffers. If it is too large to fit into what is left of the current buffer, then add it to the next buffer instead.

When the buffers are completely full, QuickDraw GX sends the GXDumpBuffer message to write the data in the buffer to the device and then sends the GXFreeBuffer message to open the buffer to write additional data.

SPECIAL CONSIDERATIONS
You can send the GXBufferData message to add data to the printer's data stream.
If you are implementing your own buffering scheme, you need to perform a total override of the GXBufferData message. Otherwise, you need to modify the data and then forward the message.

RESULT CODES
gxSegmentLoadFailedErr A required code segment could not be found,
or there was not enough memory to load it.
gxPrUserAbortErr The user has canceled printing.
gxGBBufferTooSmallErr The buffer is too small to accept the requested data, and you have specified that buffers are not to be split.

The default implementation of the GXBufferData message can also return the communications errors that are listed in Table 4-2 on page 4-42.

SEE ALSO
The GXDumpBuffer message is described on page 4-142.
The GXFreeBuffer message is described on page 4-143.

**Table 4-10 Options for adding data to the buffer**
Constant	Value	Explanation
gxNoBufferOptions	0x00000000	No options apply.
gxMakeBufferHex	0x00000001	All data is converted into ASCII hex equivalents: each byte becomes 2 ASCII bytes.
gxDontSplitBuffer	0x00000002	The data sent in this message cannot be split across buffers. If it is too large to fit into what is left of the current buffer, then add it to the next buffer instead.

gxSegmentLoadFailedErr	A required code segment could not be found, or there was not enough memory to load it.
gxPrUserAbortErr	The user has canceled printing.
gxGBBufferTooSmallErr	The buffer is too small to accept the requested data, and you have specified that buffers are not to be split.