fix vips_shrink() seq again

perhaps properly this time

ChangeLog

@@ -1,13 +1,14 @@
 12/3/13 started 7.33.0
 - vipsthumbnail lets you specify the sharpening mask
 - turn off caching for im_copy()/vips_copy(), we use copy to stop sharing, and
-it's cheap so caching doesn't help anyway
+  it's cheap so caching doesn't help anyway
 - auto rshift down to 8 bits on save, if necessary
 - im_gaussnoise(), im_copy_file(), im_grid(), im_scale(), im_scaleps(),
   im_wrap(), im_rotquad(), im_zoom(), im_subsample(), im_msb(), im_text(),
   im_system(), im_system_image()
   redone as classes
 - add --angle option to dzsave
+- another vips_shrink() fix argh
 
 14/5/13 started 7.32.4
 - icc import and export could segv on very wide images

TODO

@@ -1,58 +1,3 @@
-- try
-
-	$ vips shrink Chicago.png x.v 230 230
-	** VIPS:ERROR:vipspng.c:432:png2vips_generate: assertion failed: (r->top == read->y_pos)
-	Aborted (core dumped)
-
-$ vips shrink Chicago.png x.v 230 230 --vips-progress
-vips_sequential_class_init
-vips x.v: 127 x 18 pixels, 4 threads, 127 x 1 tiles, 1280 lines in buffer
-vips_sequential_build
-
-thread 0x24a7cf0 request for 230 lines, start line 0
-thread 0x24a7cf0 has lock ...
-thread 0x24a7cf0 reading ...
-
-thread 0x24a7ca0 request for 230 lines, start line 230
-
-thread 0x24a7d40 request for 230 lines, start line 460
-
-thread 0x24a7d90 request for 230 lines, start line 690
-
-thread 0x24a7cf0 updating y_pos to 230 and waking stalled
-thread 0x24a7cf0 unlocking ...
-
-thread 0x24a7ca0 has lock ...
-thread 0x24a7ca0 reading ...
-
-thread 0x24a7cf0 request for 230 lines, start line 0
-
-thread 0x24a7ca0 updating y_pos to 460 and waking stalled
-thread 0x24a7ca0 unlocking ...
-
-thread 0x24a7d40 has lock ...
-thread 0x24a7d40 reading ...
-
-thread 0x24a7ca0 request for 230 lines, start line 230
-
-thread 0x24a7d40 updating y_pos to 690 and waking stalled
-thread 0x24a7d40 unlocking ...
-
-thread 0x24a7d90 has lock ...
-thread 0x24a7d90 reading ...
-
-thread 0x24a7d40 request for 230 lines, start line 460
-
-thread 0x24a7d90 updating y_pos to 920 and waking stalled
-thread 0x24a7d90 unlocking ...
-
-thread 0x24a7cf0 has lock ...
-thread 0x24a7cf0 reading ...
-**
-VIPS:ERROR:vipspng.c:432:png2vips_generate: assertion failed: (r->top ==
-read->y_pos)
-Aborted (core dumped)
-
 
 - move other/im_makexy.c into copnversion? should sit with bvips_black()?
 

libvips/conversion/sequential.c

@@ -119,13 +119,13 @@ vips_sequential_generate( VipsRegion *or,
         VipsRect *r = &or->valid;
 	VipsRegion *ir = (VipsRegion *) seq;
 
-	VIPS_DEBUG_MSG( "thread %p request for %d lines, start line %d\n", 
-		g_thread_self(), r->height, r->top );
+	VIPS_DEBUG_MSG( "thread %p request for line %d, height %d\n", 
+		g_thread_self(), r->top, r->height );
 
 	if( sequential->trace )
 		vips_diag( class->nickname, 
-			"request for %d lines, starting at line %d", 
-			r->height, r->top );
+			"request for line %d, height %d", 
+			r->top, r->height );
 
 	g_mutex_lock( sequential->lock );
 

libvips/conversion/tilecache.c

@@ -863,10 +863,9 @@ vips_line_cache_gen( VipsRegion *or,
 	/* We size up the cache to the largest request.
 	 */
 	if( or->valid.height > 
-		block_cache->max_tiles * block_cache->tile_height ) {
+		block_cache->max_tiles * block_cache->tile_height ) 
 		block_cache->max_tiles = 
 			1 + (or->valid.height / block_cache->tile_height);
-	}
 
 	g_mutex_unlock( block_cache->lock );
 

libvips/resample/shrink.c

@@ -38,6 +38,9 @@
  * 	- don't change xres/yres, see comment below
  * 8/4/13
  * 	- oops demand_hint was incorrect, thanks Jan
+ * 6/6/13
+ * 	- don't chunk horizontally, fixes seq problems with large shrink
+ * 	  factors
  */
 
 /*
@@ -255,43 +258,46 @@ vips_shrink_gen( VipsRegion *or, void *vseq, void *a, void *b, gboolean *stop )
 	 * pixels, so we walk *r in chunks which map to the tile size.
 	 *
 	 * Make sure we can't ask for a zero step.
+	 *
+	 * We don't chunk horizontally. We want "vips shrink x.jpg b.jpg 100
+	 * 100" to run sequentially. If we chunk horizontally, we will fetch
+	 * 100x100 lines from the top of the image, then 100x100 100 lines
+	 * down, etc. for each thread, then when they've finished, fetch
+	 * 100x100, 100 pixels across from the top of the image. This will
+	 * break sequentiality. 
 	 */
-	int xstep = shrink->mw > VIPS__TILE_WIDTH ? 
-		1 : VIPS__TILE_WIDTH / shrink->mw;
 	int ystep = shrink->mh > VIPS__TILE_HEIGHT ? 
 		1 : VIPS__TILE_HEIGHT / shrink->mh;
 
-	int x, y;
+	int y;
 
 #ifdef DEBUG
 	printf( "vips_shrink_gen: generating %d x %d at %d x %d\n",
 		r->width, r->height, r->left, r->top ); 
 #endif /*DEBUG*/
 
-	for( y = 0; y < r->height; y += ystep )  
-		for( x = 0; x < r->width; x += xstep ) { 
-			/* Clip the this rect against the demand size.
-			 */
-			int width = VIPS_MIN( xstep, r->width - x );
-			int height = VIPS_MIN( ystep, r->height - y );
+	for( y = 0; y < r->height; y += ystep ) {
+		/* Clip the this rect against the demand size.
+		 */
+		int height = VIPS_MIN( ystep, r->height - y );
 
-			VipsRect s;
+		VipsRect s;
 
-			s.left = (r->left + x) * shrink->xshrink;
-			s.top = (r->top + y) * shrink->yshrink;
-			s.width = ceil( width * shrink->xshrink );
-			s.height = ceil( height * shrink->yshrink );
+		s.left = r->left * shrink->xshrink;
+		s.top = (r->top + y) * shrink->yshrink;
+		s.width = ceil( r->width * shrink->xshrink );
+		s.height = ceil( height * shrink->yshrink );
 #ifdef DEBUG
-			printf( "shrink_gen: requesting %d x %d at %d x %d\n",
-				s.width, s.height, s.left, s.top ); 
+		printf( "shrink_gen: requesting %d x %d at %d x %d\n",
+			s.width, s.height, s.left, s.top ); 
 #endif /*DEBUG*/
-			if( vips_region_prepare( ir, &s ) )
-				return( -1 );
+		if( vips_region_prepare( ir, &s ) )
+			return( -1 );
 
-			vips_shrink_gen2( shrink, seq, 
-				or, ir, 
-				r->left + x, r->top + y, width, height );
-		}
+		vips_shrink_gen2( shrink, seq, 
+			or, ir, 
+			r->left, r->top + y, r->width, height );
+	}
 
 	return( 0 );
 }