make bandrank work with many input images

400+ tested and seems to work

see https://github.com/jcupitt/libvips/issues/822

libvips/conversion/bandary.c

@@ -79,21 +79,6 @@
 
 G_DEFINE_ABSTRACT_TYPE( VipsBandary, vips_bandary, VIPS_TYPE_CONVERSION );
 
-/* Our sequence value.
- */
-typedef struct {
-	VipsBandary *bandary;
-
-	/* Set of input regions.
-	 */
-	VipsRegion **ir;
-
-	/* For each input, an input pointer.
-	 */
-	VipsPel **p;
-
-} VipsBandarySequence;
-
 static int
 vips_bandary_stop( void *vseq, void *a, void *b )
 {
@@ -108,6 +93,7 @@ vips_bandary_stop( void *vseq, void *a, void *b )
 	}
 
 	VIPS_FREE( seq->p );
+	VIPS_FREE( seq->pixels );
 
 	VIPS_FREE( seq );
 
@@ -129,6 +115,7 @@ vips_bandary_start( VipsImage *out, void *a, void *b )
 	seq->bandary = bandary;
 	seq->ir = NULL;
 	seq->p = NULL;
+	seq->pixels = NULL;
 
 	/* How many images?
 	 */
@@ -158,6 +145,14 @@ vips_bandary_start( VipsImage *out, void *a, void *b )
 		return( NULL );
 	}
 
+	/* Pixel buffer. This is used as working space by some subclasses.
+	 */
+	if( !(seq->pixels = VIPS_ARRAY( NULL, 
+		n * VIPS_IMAGE_SIZEOF_PEL( bandary->ready[0] ), VipsPel )) ) {
+		vips_bandary_stop( seq, NULL, NULL );
+		return( NULL );
+	}
+
 	return( seq );
 }
 
@@ -182,7 +177,7 @@ vips_bandary_gen( VipsRegion *or, void *vseq, void *a, void *b, gboolean *stop )
 	VIPS_GATE_START( "vips_bandary_gen: work" ); 
 
 	for( y = 0; y < r->height; y++ ) {
-		class->process_line( bandary, q, seq->p, r->width );
+		class->process_line( seq, q, seq->p, r->width );
 
 		for( i = 0; i < bandary->n; i++ )
 			seq->p[i] += VIPS_REGION_LSKIP( seq->ir[i] );

libvips/conversion/bandary.h

@@ -53,7 +53,27 @@ extern "C" {
 		VIPS_TYPE_BANDARY, VipsBandaryClass ))
 
 struct _VipsBandary;
-typedef void (*VipsBandaryProcessFn)( struct _VipsBandary *bandary, 
+
+/* Our sequence value.
+ */
+typedef struct {
+	struct _VipsBandary *bandary;
+
+	/* Set of input regions.
+	 */
+	VipsRegion **ir;
+
+	/* For each input, an input pointer.
+	 */
+	VipsPel **p;
+
+	/* A memory area large enough to hold one pixel from each input image.
+	 */
+	VipsPel *pixels;
+
+} VipsBandarySequence;
+
+typedef void (*VipsBandaryProcessFn)( VipsBandarySequence *seq, 
 	VipsPel *out, VipsPel **in, int width );
 
 typedef struct _VipsBandary {

libvips/conversion/bandbool.c

@@ -146,9 +146,10 @@ vips_bandbool_build( VipsObject *object )
 }
 
 static void
-vips_bandbool_buffer( VipsBandary *bandary, 
+vips_bandbool_buffer( VipsBandarySequence *seq,
 	VipsPel *out, VipsPel **in, int width )
 {
+	VipsBandary *bandary = seq->bandary;
 	VipsBandbool *bandbool = (VipsBandbool *) bandary;
 	VipsImage *im = bandary->ready[0];
 	int bands = im->Bands;

libvips/conversion/bandjoin.c

@@ -88,8 +88,10 @@ typedef VipsBandaryClass VipsBandjoinClass;
 G_DEFINE_TYPE( VipsBandjoin, vips_bandjoin, VIPS_TYPE_BANDARY );
 
 static void
-vips_bandjoin_buffer( VipsBandary *bandary, VipsPel *q, VipsPel **p, int width )
+vips_bandjoin_buffer( VipsBandarySequence *seq, 
+	VipsPel *q, VipsPel **p, int width )
 {
+	VipsBandary *bandary = seq->bandary;
 	VipsConversion *conversion = (VipsConversion *) bandary;
 	VipsImage **in = bandary->ready;
 
@@ -296,9 +298,10 @@ vips_bandjoin_const_finalize( GObject *object )
 }
 
 static void
-vips_bandjoin_const_buffer( VipsBandary *bandary, 
+vips_bandjoin_const_buffer( VipsBandarySequence *seq,
 	VipsPel *q, VipsPel **p, int width )
 {
+	VipsBandary *bandary = seq->bandary;
 	VipsConversion *conversion = (VipsConversion *) bandary;
 	VipsBandjoinConst *bandjoin = (VipsBandjoinConst *) bandary;
 	VipsImage *in = bandary->ready[0];

libvips/conversion/bandmean.c

@@ -120,9 +120,10 @@ G_DEFINE_TYPE( VipsBandmean, vips_bandmean, VIPS_TYPE_BANDARY );
 }
 
 static void
-vips_bandmean_buffer( VipsBandary *bandary, 
+vips_bandmean_buffer( VipsBandarySequence *seq, 
 	VipsPel *out, VipsPel **in, int width )
 {
+	VipsBandary *bandary = seq->bandary;
 	VipsImage *im = bandary->ready[0];
 	const int bands = im->Bands;
 	const int sz = width * 

libvips/conversion/bandrank.c

@@ -147,18 +147,18 @@ G_DEFINE_TYPE( VipsBandrank, vips_bandrank, VIPS_TYPE_BANDARY );
 /* Sort input band elements in the stack. Needs to be big enough for
  * sizeof(band-element) * number-of-images.
  */
-#define SORT_BUFFER (1024)
-
 static void
-vips_bandrank_buffer( VipsBandary *bandary, VipsPel *q, VipsPel **p, int width )
+vips_bandrank_buffer( VipsBandarySequence *seq, 
+	VipsPel *q, VipsPel **p, int width )
 {
+	VipsBandary *bandary = seq->bandary;
 	VipsBandrank *bandrank = (VipsBandrank *) bandary;
 	VipsImage **in = bandary->ready;
 	int sz = width * in[0]->Bands; 
+	VipsPel *sort_buffer = seq->pixels;
 
 	int i, j, k;
 	int x;
-	VipsPel sort_buffer[SORT_BUFFER]; 
 
 	/* Special-case max and min.
 	 */
@@ -196,15 +196,6 @@ vips_bandrank_build( VipsObject *object )
 			return( vips_bandary_copy( bandary ) );
 		}
 
-		/* We need to keep one band element for every input image 
-		 * on the stack.
-		 */
-		if( sizeof( double ) * n > SORT_BUFFER ) {
-			vips_error( class->nickname, 
-				"%s", _( "too many input images" ) );
-			return( -1 );
-		}
-
 		if( vips__bandalike_vec( class->nickname, in, band, n, 0 ) )
 			return( -1 ); 
 

libvips/conversion/extract.c

@@ -337,9 +337,10 @@ typedef VipsBandaryClass VipsExtractBandClass;
 G_DEFINE_TYPE( VipsExtractBand, vips_extract_band, VIPS_TYPE_BANDARY );
 
 static void
-vips_extract_band_buffer( VipsBandary *bandary, 
+vips_extract_band_buffer( VipsBandarySequence *seq,
 	VipsPel *out, VipsPel **in, int width )
 {
+	VipsBandary *bandary = seq->bandary;
 	VipsConversion *conversion = (VipsConversion *) bandary;
 	VipsExtractBand *extract = (VipsExtractBand *) bandary;
 	VipsImage *im = bandary->ready[0];