composite in scanlines, not pixels

try compositing a scanline at a time, should improve cache locality for
deep image stacks

seems to work, needs benchmarking

ChangeLog

@@ -9,6 +9,7 @@
 - add bandand()/or()/eor() to cplusplus binding [clcaalu]
 - implement shrink-on-load for tiff pyramids [jcupitt]
 - added vips_image_set_blob_copy() [jcupitt]
+- don't stop composite on first non-transparent image [felixbuenemann]
 
 23/9/18 started 8.7.1
 - update function list in docs [janko-m] 

libvips/conversion/composite.cpp

@@ -11,6 +11,7 @@
  * 	- x/y params let you position images
  * 27/11/18
  * 	- don't stop on first non-transparent image [felixbuenemann]
+ * 	- composite in scanlines, not pixels [jcupitt]
  */
 
 /*
@@ -163,6 +164,13 @@ typedef struct {
 	 */
 	VipsPel **p;
 
+	/* We composite images a scanline at a time, working up the image
+	 * stack. Keep intermediate pixels in this scanline buffer. 
+	 *
+	 * This will be float for the vector path, double otherwise.
+	 */
+	double *scanline;
+
 } VipsCompositeSequence;
 
 static int
@@ -179,6 +187,7 @@ vips_composite_stop( void *vseq, void *a, void *b )
 	}
 
 	VIPS_FREE( seq->p );
+	VIPS_FREE( seq->scanline );
 
 	VIPS_FREE( seq );
 
@@ -230,6 +239,14 @@ vips_composite_start( VipsImage *out, void *a, void *b )
 		return( NULL );
 	}
 
+	/* Scanline buffer.
+	 */
+	if( !(seq->scanline = 
+		VIPS_ARRAY( NULL, in[0]->Xsize * in[0]->Bands, double )) ) {
+		vips_composite_stop( seq, NULL, NULL );
+		return( NULL );
+	}
+
 	return( seq );
 }
 
@@ -329,13 +346,13 @@ vips_composite_base_max_band( VipsCompositeBase *composite, double *max_band )
  * xB	colour band of source B
  */
 
-/* A is the new pixel coming in, of any non-complex type T. 
+/* A is the new scaline coming in, of any non-complex type T. 
  *
  * We must scale incoming pixels to 0 - 1 by dividing by the scale[] vector.
  *
  * If premultipled is not set, we premultiply incoming pixels before blending.
  *
- * B is the double pixel we are accumulating. 
+ * B is the double scanline we are accumulating. 
  */
 template <typename T>
 static void
@@ -524,7 +541,8 @@ vips_composite_base_blend( VipsCompositeBase *composite,
 				double g;
 
 				if( B[b] <= 0.25 ) 
-					g = ((16 * B[b] - 12) * B[b] + 4) * B[b];
+					g = ((16 * B[b] - 12) * 
+						B[b] + 4) * B[b];
 				else 
 					g = sqrt( B[b] );
 
@@ -786,7 +804,8 @@ vips_composite_base_blend3( VipsCompositeBase *composite,
  */
 template <typename T, gint64 min_T, gint64 max_T>
 static void 
-vips_combine_pixels( VipsCompositeBase *composite, VipsPel *q, VipsPel **p )
+vips_combine_pixels( VipsCompositeBase *composite, 
+	VipsPel *q, VipsPel **p, double *scanline, int width )
 {
 	VipsBlendMode *mode = (VipsBlendMode *) composite->mode->area.data;
 	int n_mode = composite->mode->area.n;
@@ -795,61 +814,85 @@ vips_combine_pixels( VipsCompositeBase *composite, VipsPel *q, VipsPel **p )
 	T * restrict tq = (T * restrict) q;
 	T ** restrict tp = (T ** restrict) p;
 
-	double B[MAX_BANDS + 1];
-	double aB;
+	double *B1;
+	T * restrict tp1;
+	T * restrict tq1;
 
-	/* Load and scale the base pixel to 0 - 1.
+	/* Load and scale the base scanline to 0 - 1.
 	 */
-	for( int b = 0; b <= bands; b++ )
-		B[b] = tp[0][b] / composite->max_band[b];
+	B1 = scanline;
+	tp1 = tp[0];
+	for( int x = 0; x < width; x++ ) {
+		for( int b = 0; b <= bands; b++ ) 
+			B1[b] = tp1[b] / composite->max_band[b];
 
-	aB = B[bands];
-	if( !composite->premultiplied )
-		for( int b = 0; b < bands; b++ )
-			B[b] *= aB;
+		if( !composite->premultiplied ) {
+			double aB = B1[bands];
+
+			for( int b = 0; b < bands; b++ )
+				B1[b] *= aB;
+		}
+
+		B1 += bands + 1;
+		tp1 += bands + 1;
+	}
 
 	for( int i = 1; i < n; i++ ) {
 		VipsBlendMode m = n_mode == 1 ? mode[0] : mode[i - 1];
 
-		vips_composite_base_blend<T>( composite, m, B, tp[i] ); 
+		B1 = scanline;
+		tp1 = tp[i];
+		for( int x = 0; x < width; x++ ) {
+			vips_composite_base_blend<T>( composite, m, B1, tp1 ); 
+
+			B1 += bands + 1;
+			tp1 += bands + 1;
+		}
 	}
 
-	/* Unpremultiply, if necessary.
+	/* Write back as a full range pixel, clipping to range. Unpremultiply, 
+	 * if necessary.
 	 */
-	if( !composite->premultiplied ) {
-		double aR = B[bands];
+	B1 = scanline;
+	tq1 = tq;
+	for( int x = 0; x < width; x++ ) {
+		if( !composite->premultiplied ) {
+			double aR = B1[bands];
 
-		if( aR == 0 )
-			for( int b = 0; b < bands; b++ )
-				B[b] = 0;
-		else
-			for( int b = 0; b < bands; b++ )
-				B[b] = B[b] / aR;
-	}
-
-	/* Write back as a full range pixel, clipping to range.
-	 */
-	for( int b = 0; b <= bands; b++ ) {
-		double v;
-
-		v = B[b] * composite->max_band[b];
-		if( min_T != 0 || 
-			max_T != 0 ) {
-			v = VIPS_CLIP( min_T, v, max_T ); 
+			if( aR == 0 )
+				for( int b = 0; b < bands; b++ )
+					B1[b] = 0;
+			else
+				for( int b = 0; b < bands; b++ )
+					B1[b] = B1[b] / aR;
 		}
 
-		tq[b] = v;
+		for( int b = 0; b <= bands; b++ ) {
+			double v;
+
+			v = B1[b] * composite->max_band[b];
+			if( min_T != 0 || 
+				max_T != 0 ) {
+				v = VIPS_CLIP( min_T, v, max_T ); 
+			}
+
+			tq1[b] = v;
+		}
+
+		B1 += bands + 1;
+		tq1 += bands + 1;
 	}
 }
 
 #ifdef HAVE_VECTOR_ARITH
-/* Three band (four with alpha) vecvtior case. Non-double output. min_T and 
+/* Three band (four with alpha) vector case. Non-double output. min_T and 
  * max_T are the numeric range for this type. 0, 0 means no limit,
  * for example float.
  */
 template <typename T, gint64 min_T, gint64 max_T>
 static void 
-vips_combine_pixels3( VipsCompositeBase *composite, VipsPel *q, VipsPel **p )
+vips_combine_pixels3( VipsCompositeBase *composite, 
+	VipsPel *q, VipsPel **p, double *scanline, int width )
 {
 	VipsBlendMode *mode = (VipsBlendMode *) composite->mode->area.data;
 	int n_mode = composite->mode->area.n;
@@ -857,59 +900,108 @@ vips_combine_pixels3( VipsCompositeBase *composite, VipsPel *q, VipsPel **p )
 	T * restrict tq = (T * restrict) q;
 	T ** restrict tp = (T ** restrict) p;
 
-	v4f B;
-	float aB;
+	float *B1;
+	T * restrict tp1;
+	T * restrict tq1;
 
-	B[0] = tp[0][0];
-	B[1] = tp[0][1];
-	B[2] = tp[0][2];
-	B[3] = tp[0][3];
+	printf( "on vector path\n" );
 
-	/* Scale the base pixel to 0 - 1.
-	 */
-	B /= composite->max_band_vec;
-	aB = B[3];
+	B1 = (float *) scanline;
+	tp1 = tp[0];
+	for( int x = 0; x < width; x++ ) { 
+		v4f B;
+		float aB;
 
-	if( !composite->premultiplied ) {
-		B *= aB;
-		B[3] = aB;
+		B[0] = tp1[0];
+		B[1] = tp1[1];
+		B[2] = tp1[2];
+		B[3] = tp1[3];
+
+		/* Scale the base pixel to 0 - 1.
+		 */
+		B /= composite->max_band_vec;
+		aB = B[3];
+
+		if( !composite->premultiplied ) {
+			B *= aB;
+			B[3] = aB;
+		}
+
+		B1[0] = B[0];
+		B1[1] = B[1];
+		B1[2] = B[2];
+		B1[3] = B[3];
+
+		B1 += 4;
+		tp1 += 4;
 	}
 
 	for( int i = 1; i < n; i++ ) {
 		VipsBlendMode m = n_mode == 1 ? mode[0] : mode[i - 1];
 
-		vips_composite_base_blend3<T>( composite, m, B, tp[i] ); 
-	}
+		B1 = (float *) scanline;
+		tp1 = tp[i];
+		for( int x = 0; x < width; x++ ) {
+			v4f B;
 
-	/* Unpremultiply, if necessary.
-	 */
-	if( !composite->premultiplied ) {
-		float aR = B[3];
+			B[0] = B1[0];
+			B[1] = B1[1];
+			B[2] = B1[2];
+			B[3] = B1[3];
 
-		if( aR == 0 )
-			for( int b = 0; b < 3; b++ ) 
-				B[b] = 0;
-		else {
-			B /= aR;
-			B[3] = aR;
+			vips_composite_base_blend3<T>( composite, m, B, tp1 ); 
+
+			B1[0] = B[0];
+			B1[1] = B[1];
+			B1[2] = B[2];
+			B1[3] = B[3];
+
+			B1 += 4;
+			tp1 += 4;
 		}
 	}
 
-	/* Write back as a full range pixel, clipping to range.
-	 */
-	B *= composite->max_band_vec;
-	if( min_T != 0 || 
-		max_T != 0 ) {
-		float low = min_T;
-		float high = max_T;
+	B1 = (float *) scanline;
+	tq1 = tq;
+	for( int x = 0; x < width; x++ ) { 
+		v4f B;
 
-		B = VIPS_CLIP( low, B, high );
+		B[0] = B1[0];
+		B[1] = B1[1];
+		B[2] = B1[2];
+		B[3] = B1[3];
+
+		/* Unpremultiply, if necessary.
+		 */
+		if( !composite->premultiplied ) {
+			float aR = B[3];
+
+			if( aR == 0 )
+				for( int b = 0; b < 3; b++ ) 
+					B[b] = 0;
+			else {
+				B /= aR;
+				B[3] = aR;
+			}
+		}
+
+		B *= composite->max_band_vec;
+		if( min_T != 0 || 
+			max_T != 0 ) {
+			float low = min_T;
+			float high = max_T;
+
+			B = VIPS_CLIP( low, B, high );
+		}
+
+		tq1[0] = B[0];
+		tq1[1] = B[1];
+		tq1[2] = B[2];
+		tq1[3] = B[3];
+
+		B1 += 4;
+		tq1 += 4;
 	}
-
-	tq[0] = B[0];
-	tq[1] = B[1];
-	tq[2] = B[2];
-	tq[3] = B[3];
 }
 #endif /*HAVE_VECTOR_ARITH*/
 
@@ -920,7 +1012,6 @@ vips_composite_base_gen( VipsRegion *output_region,
 	VipsCompositeSequence *seq = (VipsCompositeSequence *) vseq;
 	VipsCompositeBase *composite = (VipsCompositeBase *) b;
 	VipsRect *r = &output_region->valid;
-	int ps = VIPS_IMAGE_SIZEOF_PEL( output_region->im );
 	int n = composite->in->area.n;
 
 	if( vips_reorder_prepare_many( output_region->im, seq->ir, r ) )
@@ -937,85 +1028,90 @@ vips_composite_base_gen( VipsRegion *output_region,
 		seq->p[n] = NULL;
 		q = VIPS_REGION_ADDR( output_region, r->left, r->top + y );
 
-		for( int x = 0; x < r->width; x++ ) {
-			switch( seq->ir[0]->im->BandFmt ) {
-			case VIPS_FORMAT_UCHAR: 	
+		switch( seq->ir[0]->im->BandFmt ) {
+		case VIPS_FORMAT_UCHAR: 	
 #ifdef HAVE_VECTOR_ARITH
-				if( composite->bands == 3 ) 
-					vips_combine_pixels3
-						<unsigned char, 0, UCHAR_MAX>
-						( composite, q, seq->p );
-				else
+			if( composite->bands == 3 ) 
+				vips_combine_pixels3
+					<unsigned char, 0, UCHAR_MAX>
+					( composite, q, seq->p, seq->scanline, 
+					  r->width );
+			else
 #endif 
-					vips_combine_pixels
-						<unsigned char, 0, UCHAR_MAX>
-						( composite, q, seq->p );
-				break;
-
-			case VIPS_FORMAT_CHAR: 		
 				vips_combine_pixels
-					<signed char, SCHAR_MIN, SCHAR_MAX>
-					( composite, q, seq->p );
-				break; 
+					<unsigned char, 0, UCHAR_MAX>
+					( composite, q, seq->p, seq->scanline, 
+					  r->width );
+			break;
 
-			case VIPS_FORMAT_USHORT: 	
+		case VIPS_FORMAT_CHAR: 		
+			vips_combine_pixels
+				<signed char, SCHAR_MIN, SCHAR_MAX>
+				( composite, q, seq->p, seq->scanline, 
+				  r->width );
+			break; 
+
+		case VIPS_FORMAT_USHORT: 	
 #ifdef HAVE_VECTOR_ARITH
-				if( composite->bands == 3 ) 
-					vips_combine_pixels3
-						<unsigned short, 0, USHRT_MAX>
-						( composite, q, seq->p );
-				else
+			if( composite->bands == 3 ) 
+				vips_combine_pixels3
+					<unsigned short, 0, USHRT_MAX>
+					( composite, q, seq->p, seq->scanline, 
+					  r->width );
+			else
 #endif 
-					vips_combine_pixels
-						<unsigned short, 0, USHRT_MAX>
-						( composite, q, seq->p );
-				break; 
-
-			case VIPS_FORMAT_SHORT: 	
 				vips_combine_pixels
-					<signed short, SHRT_MIN, SHRT_MAX>
-					( composite, q, seq->p );
-				break; 
+					<unsigned short, 0, USHRT_MAX>
+					( composite, q, seq->p, seq->scanline, 
+					  r->width );
+			break; 
 
-			case VIPS_FORMAT_UINT: 		
-				vips_combine_pixels
-					<unsigned int, 0, UINT_MAX>
-					( composite, q, seq->p );
-				break; 
+		case VIPS_FORMAT_SHORT: 	
+			vips_combine_pixels
+				<signed short, SHRT_MIN, SHRT_MAX>
+				( composite, q, seq->p, seq->scanline, 
+				  r->width );
+			break; 
 
-			case VIPS_FORMAT_INT: 		
-				vips_combine_pixels
-					<signed int, INT_MIN, INT_MAX>
-					( composite, q, seq->p );
-				break; 
+		case VIPS_FORMAT_UINT: 		
+			vips_combine_pixels
+				<unsigned int, 0, UINT_MAX>
+				( composite, q, seq->p, seq->scanline, 
+				  r->width );
+			break; 
 
-			case VIPS_FORMAT_FLOAT:
+		case VIPS_FORMAT_INT: 		
+			vips_combine_pixels
+				<signed int, INT_MIN, INT_MAX>
+				( composite, q, seq->p, seq->scanline, 
+				  r->width );
+			break; 
+
+		case VIPS_FORMAT_FLOAT:
 #ifdef HAVE_VECTOR_ARITH
-				if( composite->bands == 3 ) 
-					vips_combine_pixels3
-						<float, 0, USHRT_MAX>
-						( composite, q, seq->p );
-				else
+			if( composite->bands == 3 ) 
+				vips_combine_pixels3
+					<float, 0, USHRT_MAX>
+					( composite, q, seq->p, seq->scanline, 
+					  r->width );
+			else
 #endif 
-					vips_combine_pixels
-						<float, 0, 0>
-						( composite, q, seq->p );
-				break;
-
-			case VIPS_FORMAT_DOUBLE:
 				vips_combine_pixels
-					<double, 0, 0>
-					( composite, q, seq->p );
-				break;
+					<float, 0, 0>
+					( composite, q, seq->p, seq->scanline, 
+					  r->width );
+			break;
 
-			default:
-				g_assert_not_reached();
-				return( -1 );
-			}
+		case VIPS_FORMAT_DOUBLE:
+			vips_combine_pixels
+				<double, 0, 0>
+				( composite, q, seq->p, seq->scanline, 
+				  r->width );
+			break;
 
-			for( int i = 0; i < n; i++ )
-				seq->p[i] += ps;
-			q += ps;
+		default:
+			g_assert_not_reached();
+			return( -1 );
 		}
 	}