add line_user ... helps vips7 compat

so we now have a working im_draw_line_user() wrapper for the nip2
paintbox

TODO

@@ -1,3 +1,13 @@
+- we will need a fastlineuser, or have to modify nip2
+
+- try:
+
+	im = VIPS::Image.new(ARGV[0])
+	mask = im.less(240)
+	columns, rows = mask.project
+
+  with wtc.jpg, segv if libvips is compiled with -O, OK without
+
 - ink to vec etc. should work for complex .. output or accept a double-length 
   vector
 

libvips/deprecated/vips7compat.c

@@ -4554,10 +4554,8 @@ im_draw_line_user( VipsImage *image,
 	int x1, int y1, int x2, int y2, 
 	VipsPlotFn plot, void *a, void *b, void *c )
 {
-	im_error( "im_draw_line_user", 
-		"not supported ... use a VipsLine subclass instead, "
-		"or vips_line_mask()" ); 
-	return( -1 ); 
+	return( vips_line_user( image, x1, y1, x2, y2, 
+		plot, a, b, c, NULL ) ); 
 }
 
 int

libvips/draw/Makefile.am

@@ -8,6 +8,7 @@ libdraw_la_SOURCES = \
 	flood.c \
 	paintmask.c \
 	linemask.c \
+	lineuser.c \
 	im_draw_image.c \
 	im_draw_point.c \
 	im_draw_rect.c \

libvips/draw/draw.c

@@ -83,9 +83,10 @@ vips_draw_build( VipsObject *object )
 	draw->psize = VIPS_IMAGE_SIZEOF_PEL( draw->image );
 	draw->noclip = FALSE;
 
-	if( !(draw->pixel_ink = vips__vector_to_ink( 
-		class->nickname, draw->image,
-		draw->ink->data, draw->ink->n )) )
+	if( draw->ink &&
+		!(draw->pixel_ink = vips__vector_to_ink( 
+			class->nickname, draw->image,
+			draw->ink->data, draw->ink->n )) )
 		return( -1 );
 
 	return( 0 );
@@ -132,12 +133,14 @@ vips_draw_operation_init( void )
 	extern GType vips_paintmask_get_type( void ); 
 	extern GType vips_line_get_type( void ); 
 	extern GType vips_line_mask_get_type( void ); 
+	extern GType vips_line_user_get_type( void ); 
 	extern GType vips_circle_get_type( void ); 
 	extern GType vips_flood_get_type( void ); 
 
 	vips_paintmask_get_type();
 	vips_line_get_type();
 	vips_line_mask_get_type();
+	vips_line_user_get_type();
 	vips_circle_get_type();
 	vips_flood_get_type();
 }

libvips/draw/lineuser.c

@@ -0,0 +1,173 @@
+/* call a user function along a line ... useful for vips7 compat
+ *
+ * Copyright: J. Cupitt
+ * Written: 15/06/1992
+ * 22/7/93 JC
+ *	- im_incheck() added
+ * 16/8/94 JC
+ *	- im_incheck() changed to im_makerw()
+ * 24/10/03 JC
+ *	- now blends with 0-255 user
+ * 5/12/06
+ * 	- im_invalidate() after paint
+ * 6/3/10
+ * 	- don't im_invalidate() after paint, this now needs to be at a higher
+ * 	  level
+ * 28/9/10
+ * 	- gtk-doc
+ * 	- renamed as im_draw_user()
+ * 	- use Draw base class
+ * 6/2/14
+ * 	- now a subclass of VipsLine
+ * 9/2/14
+ * 	- from lineuser
+ */
+
+
+
+/*
+
+    This file is part of VIPS.
+    
+    VIPS is free software; you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+    02110-1301  USA
+
+ */
+
+/*
+
+    These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk
+
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif /*HAVE_CONFIG_H*/
+#include <vips/intl.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <vips/vips.h>
+
+#include "pdraw.h"
+#include "line.h"
+
+typedef struct _VipsLineUser {
+	VipsLine parent_object;
+
+	VipsPlotFn plot_fn;
+	void *a;
+	void *b;
+	void *c;
+
+} VipsLineUser;
+
+typedef VipsLineClass VipsLineUserClass;
+
+G_DEFINE_TYPE( VipsLineUser, vips_line_user, VIPS_TYPE_LINE );
+
+static int
+vips_line_user_plot_point( VipsLine *line, int x, int y ) 
+{
+	VipsDraw *draw = (VipsDraw *) line;
+	VipsLineUser *line_user = (VipsLineUser *) line;
+
+	return( line_user->plot_fn( draw->image, 
+		x, y, line_user->a, line_user->b, line_user->c ) ); 
+}
+
+static void
+vips_line_user_class_init( VipsLineUserClass *class )
+{
+	GObjectClass *gobject_class = G_OBJECT_CLASS( class );
+	VipsObjectClass *vobject_class = VIPS_OBJECT_CLASS( class );
+	VipsOperationClass *operation_class = (VipsOperationClass *) class;
+
+	gobject_class->set_property = vips_object_set_property;
+	gobject_class->get_property = vips_object_get_property;
+
+	vobject_class->nickname = "line_user";
+	vobject_class->description = _( "call a plot function along a line" ); 
+
+	operation_class->flags = VIPS_OPERATION_DEPRECATED;
+
+	class->plot_point = vips_line_user_plot_point; 
+
+	VIPS_ARG_POINTER( class, "plot_fn", 7, 
+		_( "Plot" ), 
+		_( "User plot function" ),
+		VIPS_ARGUMENT_REQUIRED_INPUT,
+		G_STRUCT_OFFSET( VipsLineUser, plot_fn ) ); 
+
+	VIPS_ARG_POINTER( class, "a", 8, 
+		_( "a" ), 
+		_( "first user argument" ),
+		VIPS_ARGUMENT_REQUIRED_INPUT,
+		G_STRUCT_OFFSET( VipsLineUser, a ) ); 
+
+	VIPS_ARG_POINTER( class, "b", 9, 
+		_( "b" ), 
+		_( "second user argument" ),
+		VIPS_ARGUMENT_REQUIRED_INPUT,
+		G_STRUCT_OFFSET( VipsLineUser, b ) ); 
+
+	VIPS_ARG_POINTER( class, "c", 10, 
+		_( "c" ), 
+		_( "third user argument" ),
+		VIPS_ARGUMENT_REQUIRED_INPUT,
+		G_STRUCT_OFFSET( VipsLineUser, c ) ); 
+
+}
+
+static void
+vips_line_user_init( VipsLineUser *line_user )
+{
+}
+
+/**
+ * vips_line_user:
+ * @image: image to draw on
+ * @x1: start of line
+ * @y1: start of line
+ * @x2: end of line
+ * @y2: end of line
+ * @user: plot function to call along line
+ * @a: user plot function argument 
+ * @b: user plot function argument 
+ * @c: user plot function argument 
+ *
+ * Calls a user plot function for every point on a line. This is mostly useful
+ * for vips7 compatibility. 
+ *
+ * See also: vips_line(), vips_line_mask().
+ *
+ * Returns: 0 on success, or -1 on error.
+ */
+int
+vips_line_user( VipsImage *image, 
+	int x1, int y1, int x2, int y2, 
+	VipsPlotFn plot_fn, void *a, void *b, void *c, ... )
+{
+	va_list ap;
+	int result;
+
+	va_start( ap, c );
+	result = vips_call_split( "line_user", ap, 
+		image, NULL, x1, y1, x2, y2, plot_fn, a, b, c );
+	va_end( ap );
+
+	return( result );
+}

libvips/include/vips/draw.h

@@ -51,6 +51,18 @@ int vips_line( VipsImage *image,
 int vips_line1( VipsImage *image, 
 	double ink, int x1, int y1, int x2, int y2, ... )
 	__attribute__((sentinel));
+int vips_line_mask( VipsImage *image, 
+	double *ink, int n, int x1, int y1, int x2, int y2, 
+	VipsImage *mask, ... )
+	__attribute__((sentinel));
+int vips_line_mask1( VipsImage *image, 
+	double ink, int x1, int y1, int x2, int y2, VipsImage *mask, ... )
+	__attribute__((sentinel));
+typedef int (*VipsPlotFn)( VipsImage *, int, int, void *, void *, void * ); 
+int vips_line_user( VipsImage *image, 
+	int x1, int y1, int x2, int y2, 
+	VipsPlotFn plot_fn, void *a, void *b, void *c, ... )
+	__attribute__((sentinel));
 
 int vips_circle( VipsImage *image, 
 	double *ink, int n, int cx, int cy, int radius, ... )