libjpeg API: Partial scanline decompression
This, in combination with the existing jpeg_skip_scanlines() function,
provides the ability to crop the image both horizontally and vertically
while decompressing (certain restrictions apply-- see libjpeg.txt.)
This also cleans up the documentation of the line skipping feature and
removes the "strip decompression" feature from djpeg, since the new
cropping feature is a superset of it.
Refer to #34 for discussion.
Closes #34
diff --git a/jdinput.c b/jdinput.c
index 23c4bf2..32a6b42 100644
--- a/jdinput.c
+++ b/jdinput.c
@@ -4,7 +4,8 @@
* This file was part of the Independent JPEG Group's software:
* Copyright (C) 1991-1997, Thomas G. Lane.
* libjpeg-turbo Modifications:
- * Copyright (C) 2010, D. R. Commander.
+ * Copyright (C) 2010, 2016, D. R. Commander.
+ * Copyright (C) 2015, Google, Inc.
* For conditions of distribution and use, see the accompanying README.ijg
* file.
*
@@ -105,6 +106,11 @@
compptr->height_in_blocks = (JDIMENSION)
jdiv_round_up((long) cinfo->image_height * (long) compptr->v_samp_factor,
(long) (cinfo->max_v_samp_factor * DCTSIZE));
+ /* Set the first and last MCU columns to decompress from multi-scan images.
+ * By default, decompress all of the MCU columns.
+ */
+ cinfo->master->first_MCU_col[ci] = 0;
+ cinfo->master->last_MCU_col[ci] = compptr->width_in_blocks - 1;
/* downsampled_width and downsampled_height will also be overridden by
* jdmaster.c if we are doing full decompression. The transcoder library
* doesn't use these values, but the calling application might.