canon_dr: DR-2580C pads the backside of duplex scans

ChangeLog

@@ -1,3 +1,7 @@
+2011-11-01 m. allan noah <kitno455 at gmail dot com>
+	* backend/canon_dr.[ch]: backend v39
+	- DR-2580C pads the backside of duplex scans
+
 2011-10-21 Stéphane Voltz <stef.dev@free.fr>
 	* backend/genesys.c backend/genesys.h backend/genesys_devices.c
 	backend/genesys_gl*.c backend/genesys_gl843.h

backend/canon_dr.c

@@ -1174,6 +1174,8 @@ init_model (struct scanner *s)
     s->duplex_interlace = DUPLEX_INTERLACE_FBFB;
     s->need_ccal = 1;
     s->need_fcal = 1;
+    s->duplex_offset = 432;
+    s->duplex_offset_side = SIDE_BACK;
 
     /*lies*/
     s->can_halftone=0;
@@ -3235,7 +3237,7 @@ update_params(struct scanner *s, int calib)
       memcpy(&s->i,&s->u,sizeof(struct img_params));
       /*dumb scanners pad the top of front page in duplex*/
       if(s->i.source == SOURCE_ADF_DUPLEX)
-        s->i.skip_lines[0] = s->duplex_offset * s->i.dpi_y / 1200;
+        s->i.skip_lines[s->duplex_offset_side] = s->duplex_offset * s->i.dpi_y / 1200;
     }
 
     DBG (15, "update_params: i params: w:%d h:%d m:%d f:%d b:%d\n",

backend/canon_dr.h

@@ -194,6 +194,7 @@ struct scanner
   int duplex_interlace; /* different models interlace sides differently      */
   int jpeg_interlace;   /* different models interlace jpeg sides differently */
   int duplex_offset;    /* number of lines of padding added to front (1/1200)*/
+  int duplex_offset_side; /* padding added to front or back? */
 
   int sw_lut;           /* no hardware brightness/contrast support */
   int bg_color;         /* needed to fill in after rotation */