support tiffsave_buffer pyramids

add support for tiff pyramid save to memory, thanks bubba

see https://github.com/jcupitt/libvips/issues/702

ChangeLog

@@ -13,6 +13,7 @@
 - add vips_find_trim(), search for non-background areas 
 - remove lcms1 support, it had bitrotted
 - `join` tagged as seq
+- support tiffsave_buffer for pyramids, thanks bubba
 
 2/8/17 started 8.5.8
 - fix transparency detection in merge, thanks Haida

libvips/foreign/tiff.c

@@ -2,6 +2,9 @@
  *
  * 14/10/16
  * 	- from vips2tiff.c
+ *
+ * 26/8/17
+ * 	- add openout_read, to help tiffsave_buffer for pyramids
  */
 
 /*
@@ -309,9 +312,26 @@ typedef struct _VipsTiffOpenoutBuffer {
 static tsize_t 
 openout_buffer_read( thandle_t st, tdata_t data, tsize_t size )
 {
-	g_assert_not_reached(); 
-	
-	return( 0 ); 
+	VipsTiffOpenoutBuffer *buffer = (VipsTiffOpenoutBuffer *) st;
+
+	off_t write_point;
+	size_t available;
+	unsigned char *from;
+
+	write_point = vips_dbuf_tell( &buffer->dbuf ); 
+	from = vips_dbuf_get_write( &buffer->dbuf, &available );
+	vips_dbuf_seek( &buffer->dbuf, write_point, SEEK_SET ); 
+
+	if( available < size ) { 
+		vips_error( "openout_buffer_read", 
+			"%s", _( "read beyond end of buffer" ) );
+		return( 0 );
+	}
+
+	memcpy( data, from, size ); 
+
+	vips_dbuf_seek( &buffer->dbuf, size, SEEK_CUR );                                 
+	return( size );
 }
 
 static tsize_t 

libvips/foreign/vips2tiff.c

@@ -171,6 +171,8 @@
  * 29/1/17
  * 	- enable bigtiff automatically for large, uncompressed writes, thanks 
  * 	  AndreasSchmid1 
+ * 26/8/17
+ * 	- support pyramid creation to buffer, thanks bubba
  */
 
 /*
@@ -1665,8 +1667,16 @@ wtiff_gather( Wtiff *wtiff )
 			printf( "Appending layer %s ...\n", layer->lname );
 #endif /*DEBUG*/
 
-			if( !(in = vips__tiff_openin( layer->lname )) ) 
-				return( -1 );
+			if( layer->lname ) {
+				if( !(in = vips__tiff_openin( layer->lname )) ) 
+					return( -1 );
+			}
+			else {
+				if( !(in = vips__tiff_openin_buffer( wtiff->im,
+					layer->buf, layer->len )) ) 
+					return( -1 );
+			}
+
 			if( wtiff_copy_tiff( wtiff, wtiff->layer->tif, in ) ) {
 				TIFFClose( in );
 				return( -1 );

libvips/iofuncs/dbuf.c

@@ -299,10 +299,10 @@ vips_dbuf_truncate( VipsDbuf *dbuf )
 }
 
 /**
- * vips_dbuf_truncate:
+ * vips_dbuf_tell:
  * @dbuf: the buffer
  *
- * Truncate the data so that it ends at the write point. No memory is freed. 
+ * Returns: the current write point
  */
 off_t
 vips_dbuf_tell( VipsDbuf *dbuf )