add low/high to smartcrop

smartcrop attention had a centre setting, but not low or high

see https://github.com/libvips/libvips/issues/1089

ChangeLog

@@ -1,4 +1,6 @@
 21/9/18 started 8.8.0
+- much faster smartcrop [lovell]
+- add low/high to smartcrop [jcupitt]
 
 23/9/18 started 8.7.1
 - update function list in docs [janko-m] 

libvips/conversion/smartcrop.c

@@ -8,6 +8,10 @@
  * 	- revised attention smartcrop
  * 8/6/17
  * 	- revised again
+ * 15/9/18 lovell
+ * 	- move shrink to start of processing
+ * 22/9/18 jcupitt
+ * 	- add low and high
  */
 
 /*
@@ -352,6 +356,16 @@ vips_smartcrop_build( VipsObject *object )
 			return( -1 );
 		break;
 
+	case VIPS_INTERESTING_LOW:
+		left = 0;
+		top = 0;
+		break;
+
+	case VIPS_INTERESTING_HIGH:
+		left = smartcrop->in->Xsize - smartcrop->width;
+		top = smartcrop->in->Ysize - smartcrop->height;
+		break;
+
 	default:
 		g_assert_not_reached();
 

libvips/include/vips/conversion.h

@@ -99,6 +99,8 @@ typedef enum {
 	VIPS_INTERESTING_CENTRE,
 	VIPS_INTERESTING_ENTROPY,
 	VIPS_INTERESTING_ATTENTION,
+	VIPS_INTERESTING_LOW,
+	VIPS_INTERESTING_HIGH,
 	VIPS_INTERESTING_LAST
 } VipsInteresting;
 

libvips/iofuncs/enumtypes.c

@@ -364,6 +364,8 @@ vips_interesting_get_type( void )
 			{VIPS_INTERESTING_CENTRE, "VIPS_INTERESTING_CENTRE", "centre"},
 			{VIPS_INTERESTING_ENTROPY, "VIPS_INTERESTING_ENTROPY", "entropy"},
 			{VIPS_INTERESTING_ATTENTION, "VIPS_INTERESTING_ATTENTION", "attention"},
+			{VIPS_INTERESTING_LOW, "VIPS_INTERESTING_LOW", "low"},
+			{VIPS_INTERESTING_HIGH, "VIPS_INTERESTING_HIGH", "high"},
 			{VIPS_INTERESTING_LAST, "VIPS_INTERESTING_LAST", "last"},
 			{0, NULL, NULL}
 		};