Release Notes

Open Source Used In AsyncOS 8.8 for Cisco Web Security Appliances
54
order. If the source data must be read in bottom-to-top order, you can use
the JPEG library's virtual array mechanism to invert the data efficiently.
Examples of this can be found in the sample application cjpeg.
The library maintains a count of the number of scanlines written so far
in the next_scanline field of the JPEG object. Usually you can just use
this variable as the loop counter, so that the loop test looks like
"while (cinfo.next_scanline < cinfo.image_height)".
Code for this step depends heavily on the way that you store the source data.
example.c shows the following code for the case of a full-size 2-D source
array containing 3-byte RGB pixels:
JSAMPROW row_pointer[1];/* pointer to a single row */
int row_stride;/* physical row width in buffer */
row_stride = image_width * 3;/* JSAMPLEs per row in image_buffer */
while (cinfo.next_scanline < cinfo.image_height) {
 row_pointer[0] = & image_buffer[cinfo.next_scanline * row_stride];
 jpeg_write_scanlines(&cinfo, row_pointer, 1);
}
jpeg_write_scanlines() returns the number of scanlines actually written.
This will normally be equal to the number passed in, so you can usually
ignore the return value. It is different in just two cases:
* If you try to write more scanlines than the declared image height,
the additional scanlines are ignored.
* If you use a suspending data destination manager, output buffer overrun
will cause the compressor to return before accepting all the passed lines.
This feature is discussed under "I/O suspension", below. The normal
stdio destination manager will NOT cause this to happen.
In any case, the return value is the same as the change in the value of
next_scanline.
6. jpeg_finish_compress(...);
After all the image data has been written, call jpeg_finish_compress() to
complete the compression cycle. This step is ESSENTIAL to ensure that the
last bufferload of data is written to the data destination.
jpeg_finish_compress() also releases working memory associated with the JPEG
object.
Typical code:
jpeg_finish_compress(&cinfo);