add VIPS_ARGUMENT_MODIFY

a flag for arguments meaning the operator will modify an input

the python binding uses this to take a copy of the arg before calling

ChangeLog

@@ -5,6 +5,8 @@
 - return of vips_init(), but just for bindings
 - revised type.c to make it more binding-friendly
 - add @background arg to save: the colour to flatten against
+- add VIPS_ARGUMENT_MODIFY flag ... used for draw_circle etc, meaning an op
+  which modifies its argument
 
 8/9/14 started 7.40.9
 - support jfif resunit "none"

libvips/draw/draw.c

@@ -115,7 +115,7 @@ vips_draw_class_init( VipsDrawClass *class )
 	VIPS_ARG_IMAGE( class, "image", 1, 
 		_( "Image" ), 
 		_( "Image to draw on" ),
-		VIPS_ARGUMENT_REQUIRED_INPUT, 
+		VIPS_ARGUMENT_REQUIRED_INPUT | VIPS_ARGUMENT_MODIFY, 
 		G_STRUCT_OFFSET( VipsDraw, image ) );
 
 }

libvips/include/vips/object.h

@@ -63,7 +63,8 @@ typedef enum /*< flags >*/ {
 	VIPS_ARGUMENT_SET_ALWAYS = 8,
 	VIPS_ARGUMENT_INPUT = 16,
 	VIPS_ARGUMENT_OUTPUT = 32,
-	VIPS_ARGUMENT_DEPRECATED = 64
+	VIPS_ARGUMENT_DEPRECATED = 64,
+	VIPS_ARGUMENT_MODIFY = 128
 } VipsArgumentFlags;
 
 /* Useful flag combinations. User-visible ones are:

libvips/iofuncs/enumtypes.c

@@ -743,6 +743,7 @@ vips_argument_flags_get_type( void )
 			{VIPS_ARGUMENT_INPUT, "VIPS_ARGUMENT_INPUT", "input"},
 			{VIPS_ARGUMENT_OUTPUT, "VIPS_ARGUMENT_OUTPUT", "output"},
 			{VIPS_ARGUMENT_DEPRECATED, "VIPS_ARGUMENT_DEPRECATED", "deprecated"},
+			{VIPS_ARGUMENT_MODIFY, "VIPS_ARGUMENT_MODIFY", "modify"},
 			{0, NULL, NULL}
 		};
 		

libvips/iofuncs/object.c

@@ -169,6 +169,7 @@
  * @VIPS_ARGUMENT_INPUT: is an input argument (one we depend on)
  * @VIPS_ARGUMENT_OUTPUT: is an output argument (depends on us)
  * @VIPS_ARGUMENT_DEPRECATED: just there for back-compat, hide 
+ * @VIPS_ARGUMENT_MODIFY: the input argument will be modified
  *
  * Flags we associate with each object argument.
  *
@@ -186,6 +187,9 @@
  * looked for if required, are not checked for "have-been-set". You can
  * deprecate a required argument, but you must obviously add a new required
  * argument if you do.
+ *
+ * Input args with @VIPS_ARGUMENT_MODIFY will be modified by the operation.
+ * This is used for things like the in-place drawing operations. 
  */
 
 /* Our signals. 

python/vips8/vips.py

@@ -79,6 +79,11 @@ class Argument:
             if not isinstance(value, Vips.Blob):
                 value = Vips.Blob.new(None, value)
 
+        # MODIFY input images need to be copied before assigning them
+        if self.flags & Vips.ArgumentFlags.MODIFY:
+            print 'taking copy of MODIFY image arg'
+            value = value.copy()
+
         logging.debug('assigning %s' % self.prop.value_type)
 
         self.op.props.__setattr__(self.name, value)
@@ -171,16 +176,18 @@ def _call_base(name, required, optional, self = None, option_string = None):
     args = [Argument(op2, x) for x in op2.props]
     args.sort(lambda a, b: a.priority - b.priority)
 
-    # find all required output args 
-    # we can't check assigned here (since we captured the value before the call)
-    # but the getattr will test that for us anyway
-    required_output = [x for x in args if x.flags & enm.OUTPUT and 
-                       x.flags & enm.REQUIRED]
-
     # gather output args 
     out = []
-    for x in required_output:
-        out.append(x.get_value())
+
+    for x in args:
+        # required output arg
+        if x.flags & enm.OUTPUT and x.flags & enm.REQUIRED:
+            out.append(x.get_value())
+
+        # modified input arg ... this will get the result of the copy() we 
+        # did above
+        if x.flags & enm.INPUT and x.flags & enm.MODIFY:
+            out.append(x.get_value())
 
     # find all optional output args 
     optional_output = [x.name for x in args if x.flags & enm.OUTPUT and