correcting vertical scanning start point

ChangeLog

@@ -1,3 +1,9 @@
+2004-10-18  Ullrich Sigwanz <usigwanz@freesurf.ch>
+
+        * backend/niash_core.c: 
+        * backend/niash.c: correcting vertical scanning start 
+          point for changed max. page height
+
 2004-10-17  Ullrich Sigwanz <usigwanz@freesurf.ch>
 
         * backend/niash_core.c: using exact number of lines

backend/niash.c

@@ -1290,7 +1290,7 @@ sane_start (SANE_Handle h)
 
   s->ScanParams.iWidth = par.pixels_per_line * iScaleDown;
   s->ScanParams.iHeight = par.lines * iScaleDown;
-  s->ScanParams.iBottom = 14200UL;
+  s->ScanParams.iBottom = HP3300C_BOTTOM;
   s->ScanParams.fCalib = SANE_FALSE;
 
   /* perform a simple calibration just before scanning */

backend/niash_core.c

@@ -977,6 +977,20 @@ CircBufferGetLine (int iHandle, TDataPipe * p, unsigned char *pabLine,
 }
 
 
+/* try to keep the number of transfers the same, but make them all 
+   as good as possible the same size to avoid cranking in critical
+   situations
+*/
+static int
+_OptimizeXferSize (int iLines, int iLinesPerXfer)
+{
+  int iXfers;
+  iXfers = (iLines + iLinesPerXfer - 1) / iLinesPerXfer;
+  while (--iLinesPerXfer > 0
+	 && (iLines + iLinesPerXfer - 1) / iLinesPerXfer == iXfers);
+  return iLinesPerXfer + 1;
+}
+
 STATIC void
 CircBufferInit (int iHandle, TDataPipe * p,
 		int iWidth, int iHeight,
@@ -1052,6 +1066,10 @@ CircBufferInit (int iHandle, TDataPipe * p,
 	{
 	  p->iLinesPerXferBuf = MAX_LINES_PER_XFERBUF;
 	}
+      /* final optimization to keep critical scans smooth */
+      p->iLinesPerXferBuf =
+	_OptimizeXferSize (p->iLinesLeft, p->iLinesPerXferBuf);
+
       DBG (DBG_MSG, "_iXFerSize = %d for %d transfer(s)\n",
 	   (int) p->iLinesPerXferBuf * p->iBytesPerLine,
 	   (p->iLinesLeft + p->iLinesPerXferBuf - 1) / p->iLinesPerXferBuf);