Tile generation did not work with TJXFORM_HFLIP, because the underlying transform code was using an in-place algorithm, which modified the source coefficients after the first tile was generated. Thus, create a new option which allows TurboJPEG to turn off the in-place horizontal flip if there are multiple transforms being performed from the same set of coefficients.

jpegtran.c

@@ -142,6 +142,7 @@ parse_switches (j_compress_ptr cinfo, int argc, char **argv,
   transformoption.trim = FALSE;
   transformoption.force_grayscale = FALSE;
   transformoption.crop = FALSE;
+  transformoption.slow_hflip = FALSE;
   cinfo->err->trace_level = 0;
 
   /* Scan command line options, adjust parameters */

transupp.c

@@ -1022,7 +1022,7 @@ jtransform_request_workspace (j_decompress_ptr srcinfo,
   case JXFORM_FLIP_H:
     if (info->trim)
       trim_right_edge(info, srcinfo->output_width);
-    if (info->y_crop_offset != 0)
+    if (info->y_crop_offset != 0 || info->slow_hflip)
       need_workspace = TRUE;
     /* do_flip_h_no_crop doesn't need a workspace array */
     break;
@@ -1448,7 +1448,7 @@ jtransform_execute_transform (j_decompress_ptr srcinfo,
 	      src_coef_arrays, dst_coef_arrays);
     break;
   case JXFORM_FLIP_H:
-    if (info->y_crop_offset != 0)
+    if (info->y_crop_offset != 0 || info->slow_hflip)
       do_flip_h(srcinfo, dstinfo, info->x_crop_offset, info->y_crop_offset,
 		src_coef_arrays, dst_coef_arrays);
     else

transupp.h

@@ -128,6 +128,13 @@ typedef struct {
   boolean trim;			/* if TRUE, trim partial MCUs as needed */
   boolean force_grayscale;	/* if TRUE, convert color image to grayscale */
   boolean crop;			/* if TRUE, crop source image */
+  boolean slow_hflip;  /* For best performance, the JXFORM_FLIP_H transform
+                          normally modifies the source coefficients in place.
+                          Setting this to TRUE will instead use a slower,
+                          double-buffered algorithm, which leaves the source
+                          coefficients in tact (necessary if other transformed
+                          images must be generated from the same set of
+                          coefficients. */
 
   /* Crop parameters: application need not set these unless crop is TRUE.
    * These can be filled in by jtransform_parse_crop_spec().

turbojpegl.c

@@ -751,6 +751,8 @@ DLLEXPORT int DLLCALL tjTransform(tjhandle hnd,
 		xinfo[i].trim=(t[i].options&TJXFORM_TRIM)? 1:0;
 		xinfo[i].force_grayscale=(t[i].options&TJXFORM_GRAY)? 1:0;
 		xinfo[i].crop=(t[i].options&TJXFORM_CROP)? 1:0;
+		if(n!=1 && t[i].op==TJXFORM_HFLIP) xinfo[i].slow_hflip=1;
+		else xinfo[i].slow_hflip=0;
 
 		if(xinfo[i].crop)
 		{