move C API back to int operations

always return results through params

ChangeLog

@@ -8,6 +8,7 @@
 - in im_vips2tiff, enable YCbCr compression for jpeg write
 - VipsMin stops search early if it can
 - C API supports optional output args
+- switch back to int-valued operations
 
 10/8/11 started 7.26.3
 - don't use G_VALUE_COLLECT_INIT(), many platforms do not have a glib this

TODO

@@ -1,25 +1,4 @@
-- is our C API too awkward? we'll need
-
-	if( !(c = vips_add( a, b )) ||
-		!(d = vips_add( a, c )) )
-		return NULL;
-
-  seems wordy compared to 
-
-	if( vips_add( a, b, &c ) ||
-		vips_add( a, c, &d ) )
-		return -1;
-
-  plus VipsPool will be more natural with #2, I think, and things like
-  vips_avg() have to be form #2
-
-  also, we have
-
-  	if( vips_call( "add", a, b, &c ) ||
-		vips_call( "add", a, c, &d ) )
-		return( -1 );
-
-  which is much closer to #2
+- revise vipspool, write a test prog
 
 
 

libvips/arithmetic/add.c

@@ -321,19 +321,15 @@ vips_add_init( VipsAdd *add )
 {
 }
 
-VipsImage *
-vips_add( VipsImage *in1, VipsImage *in2, ... )
+int
+vips_add( VipsImage *in1, VipsImage *in2, VipsImage **out, ... )
 {
 	va_list ap;
 	int result;
-	VipsImage *out;
 
-	va_start( ap, in2 );
-	result = vips_call_split( "add", ap, in1, in2, &out );
+	va_start( ap, out );
+	result = vips_call_split( "add", ap, in1, in2, out );
 	va_end( ap );
 
-	if( result )
-		return( NULL );
-
-	return( out );
+	return( result );
 }

libvips/arithmetic/subtract.c

@@ -254,24 +254,20 @@ vips_subtract_class_init( VipsSubtractClass *class )
 	bclass->process_line = subtract_buffer;
 }
 
-VipsImage *
-vips_subtract( VipsImage *in1, VipsImage *in2, ... )
-{
-	va_list ap;
-	int result;
-	VipsImage *out;
-
-	va_start( ap, in2 );
-	result = vips_call_split( "subtract", ap, in1, in2, &out );
-	va_end( ap );
-
-	if( result )
-		return( NULL );
-
-	return( out );
-}
-
 static void
 vips_subtract_init( VipsSubtract *subtract )
 {
 }
+
+int
+vips_subtract( VipsImage *in1, VipsImage *in2, VipsImage **out, ... )
+{
+	va_list ap;
+	int result;
+
+	va_start( ap, in2 );
+	result = vips_call_split( "subtract", ap, in1, in2, out );
+	va_end( ap );
+
+	return( result );
+}

libvips/include/vips/arithmetic.h

@@ -37,8 +37,8 @@
 extern "C" {
 #endif /*__cplusplus*/
 
-VipsImage *vips_add( VipsImage *in1, VipsImage *in2, ... );
-VipsImage *vips_subtract( VipsImage *in1, VipsImage *in2, ... );
+int vips_add( VipsImage *in1, VipsImage *in2, VipsImage **out, ... );
+int vips_subtract( VipsImage *in1, VipsImage *in2, VipsImage **out, ... );
 int vips_avg( VipsImage *in, double *out, ... );
 int vips_min( VipsImage *in, double *out, ... );
 

libvips/iofuncs/pool.c

@@ -53,21 +53,20 @@
 
   Here's how to handle ref counts when calling vips operations:
 
-	VipsImage *
-	thing( VipsImage *in1, VipsImage *in2 )
+	int
+	thing( VipsImage *in1, VipsImage *in2, VipsImage **out )
 	{
 		VipsImage *t;
-		VipsImage *out;
 
 		if( vips_add( in1, in2, &t, NULL ) )
-			return( NULL );
-		if( vips_add( in1, t, &out, NULL ) ) {
+			return( -1 );
+		if( vips_add( in1, t, out, NULL ) ) {
 			g_object_unref( t );
-			return( NULL );
+			return( -1 );
 		}
 		g_object_unref( t );
 
-		return( out );
+		return( 0 );
 	}
 
   The first vips_add() call returns (via the reference argument) a new 
@@ -79,18 +78,16 @@
   VipsPool provides a nicer way to track the objects that you create and free 
   them safely. The above function would become:
 
-  	VipsImage *
-	thing( VipsPool *pool, VipsImage *in1, VipsImage *in2 )
+  	int
+	thing( VipsPool *pool, VipsImage *in1, VipsImage *in2, VipsImage **out )
 	{
 		VipsPoolContext *context = vips_pool_context_new( pool );
 
-		VipsImage *out;
-
 		if( vips_add( in1, in2, VIPS_VAR_IMAGE_REF( 1 ), NULL ) ||
-			vips_add( in1, VIPS_VAR_IMAGE( 1 ), &out, NULL ) )
-			return( NULL );
+			vips_add( in1, VIPS_VAR_IMAGE( 1 ), out, NULL ) )
+			return( -1 );
 
-		return( out );
+		return( 0 );
 	}
 
   vips_pool_context_new() creates a new context to hold a set of temporary