[gs-cvs] rev 7016 - trunk/gs/src

[leonardo at ghostscript.com]

Author: leonardo
Date: 2006-08-31 03:34:11 -0700 (Thu, 31 Aug 2006)
New Revision: 7016

Modified:
   trunk/gs/src/gspaint.c
Log:
Fix : Improving the documentation about computing a text object tag in gspaint.c .

DETAILS :

It's how I understand it while communicating with Stefan and Henry.
I'll post it to code review for possible further improvements.
 
EXPECTED DIFFERENCES :

None.


Modified: trunk/gs/src/gspaint.c
===================================================================
--- trunk/gs/src/gspaint.c	2006-08-31 09:53:51 UTC (rev 7015)
+++ trunk/gs/src/gspaint.c	2006-08-31 10:34:11 UTC (rev 7016)
@@ -269,10 +269,33 @@
 	code = 0;
     } else {
 	int abits, acode, rcode = 0;
-        /* to distinguish text from vectors we hackly look at the
-           target device 1 bit per component is a cache and this is
-           text else it is a path */
 
+	/* Here we need to distinguish text from vectors to compute the object tag.
+	   Actually we need to know whether this function is called to rasterize a character,
+	   or to rasterize a vector graphics to the output device.
+	   Currently we assume it works for the bitrgbtags device only,
+	   which is a low level device with a 4-component color model.
+	   We use the fact that with printers a character is usually being rendered 
+	   to a 1bpp cache device rather than to the output device.
+	   Therefore we hackly look whether the target device
+	   "has a color" : either it's a multicomponent color model,
+	   or it is not gray (such as a yellow separation).
+
+	   This check has several limitations :
+	   1. It doesn't work with -dNOCACHE.
+	   2. It doesn't work with large characters,
+	      which cannot fit into a cache cell and thus they
+	      render directly to the output device.
+	   3. It doesn't work for TextAlphaBits=2 or 4.
+	      We don't care of this case because
+	      text antialiasing usually usn't applied to printers.
+	   4. It doesn't work for things like with "(xyz) true charpath stroke".
+	      That's unfortunate, we'd like to improve someday.
+	   5. It doesn't work for high level devices when a Type 3 character is being constructed.
+	      This case is not important for low level devices
+	      (which a printer is), because low level device doesn't accept
+	      Type 3 charproc streams immediately.
+	 */
         if (gx_device_has_color(gs_currentdevice(pgs))) {
 	    gx_unset_dev_color(pgs);
             gs_set_object_tag(pgs, GS_PATH_TAG);