small optimzing of drawing line by George Veskov (jkxxster at gmail dot com) irc nick jkxx

svn path=/trunk/; revision=25110

reactos/dll/win32/gdi32/objects/linedda.c

@@ -43,7 +43,44 @@ BOOL STDCALL LineDDA(INT nXStart, INT nYStart, INT nXEnd, INT nYEnd,
     INT cnt;
     INT dx = nXEnd - nXStart;
     INT dy = nYEnd - nYStart;
-
+	
+	// optimized for vertical and horizontal lines so we avoid unnecessary math
+	if(nXStart == nXEnd)
+	{
+	  // vertical line - use dx,dy as temp variables so we don't waste stack space
+	  if(nYStart < nYEnd)
+	  {
+	    dx = nYStart;
+	    dy = nYEnd;
+	  } else {
+	    dx = nYEnd;
+	    dy = nYStart;
+	  }
+	  for(cnt = dx; cnt <= dy; cnt++)
+	  {
+	   lpLineFunc(nXStart,cnt,lpData);
+	  } 
+	  return TRUE;
+	}
+	
+	if(nYStart == nYEnd)
+	{
+	  // horizontal line - use dx,dy as temp variables so we don't waste stack space
+	  if(nXStart < nXEnd)
+	  {
+	    dx = nXStart;
+	    dy = nXEnd;
+	  } else {
+	    dx = nXEnd;
+	    dy = nXStart;
+	  }
+	  for(cnt = dx; cnt <= dy; cnt++)
+	  {
+	   lpLineFunc(cnt, nYStart,lpData);
+	  }
+	  return TRUE;
+	}
+	// end of H/V line code
     if (dx < 0)  {
       dx = -dx; xadd = -1;
     }