revise loader demand hints

Add a check that header and load methods agree on the demand hint, and
make sure all loaders pass.

If they disagree, you can get bad performance in some cases, since the
pipeline can be built from the header dhint.

libvips/foreign/analyze2vips.c

@@ -552,6 +552,9 @@ vips__analyze_read_header( const char *filename, VipsImage *out )
 
 	attach_meta( out, d );
 
+        if( vips_image_pipelinev( out, VIPS_DEMAND_STYLE_THINSTRIP, NULL ) )
+		return( -1 );
+
 	return( 0 );
 }
 

libvips/foreign/foreign.c

@@ -932,13 +932,17 @@ vips_foreign_load_temp( VipsForeignLoad *load )
 static gboolean
 vips_foreign_load_iscompat( VipsImage *a, VipsImage *b )
 {
+        /* dhint must match too, or we can get terrible performance with some
+         * formats.
+         */
 	if( a->Xsize != b->Xsize ||
 		a->Ysize != b->Ysize ||
 		a->Bands != b->Bands ||
 		a->Coding != b->Coding ||
-		a->BandFmt != b->BandFmt ) {
+		a->BandFmt != b->BandFmt ||
-		vips_error( "VipsForeignLoad",
+                a->dhint != b->dhint ) {
-			"%s", _( "images do not match" ) ); 
+		vips_error( "VipsForeignLoad", "%s", 
+                        _( "images do not match between header and load" ) ); 
 		return( FALSE );
 	}
 

libvips/foreign/jp2kload.c

@@ -447,11 +447,9 @@ vips_foreign_load_jp2k_set_header( VipsForeignLoadJp2k *jp2k, VipsImage *out )
 		return( -1 );
 	}
 
-	/* Even though this is a tiled reader, we hint thinstrip since with
+	/* We use a tilecache on our output.
-	 * the cache we are quite happy serving that if anything downstream 
-	 * would like it.
 	 */
-        if( vips_image_pipelinev( out, VIPS_DEMAND_STYLE_THINSTRIP, NULL ) )
+        if( vips_image_pipelinev( out, VIPS_DEMAND_STYLE_SMALLTILE, NULL ) )
 		return( -1 );
 
 	vips_image_init_fields( out,

libvips/foreign/matlab.c

@@ -220,6 +220,11 @@ mat2vips_get_header( matvar_t *var, VipsImage *im )
 		 format,
 		 VIPS_CODING_NONE, interpretation, 1.0, 1.0 );
 
+        /* We read to a huge memory area.
+         */
+	if( vips_image_pipelinev( im, VIPS_DEMAND_STYLE_ANY, NULL ) )
+		return( -1 );
+
 	return( 0 );
 }
 

libvips/foreign/niftiload.c

@@ -482,7 +482,10 @@ vips_foreign_load_nifti_set_header( VipsForeignLoadNifti *nifti,
 	printf( "get_vips_properties: fmt = %d\n", fmt );
 #endif /*DEBUG*/
 
-	vips_image_pipelinev( out, VIPS_DEMAND_STYLE_SMALLTILE, NULL );
+        /* We load to memory then write to out, so we'll hint THINSTRIP.
+         */
+	vips_image_pipelinev( out, VIPS_DEMAND_STYLE_THINSTRIP, NULL );
+
 	vips_image_init_fields( out,
 		width, height, bands, fmt, 
 		VIPS_CODING_NONE, 

libvips/foreign/popplerload.c

@@ -277,11 +277,6 @@ vips_foreign_load_pdf_set_image( VipsForeignLoadPdf *pdf, VipsImage *out )
 	printf( "vips_foreign_load_pdf_set_image: %p\n", pdf );
 #endif /*DEBUG*/
 
-	/* We render to a linecache, so fat strips work well.
-	 */
-        if( vips_image_pipelinev( out, VIPS_DEMAND_STYLE_FATSTRIP, NULL ) )
-		return( -1 );
-
 	/* Extract and attach metadata. Set the old name too for compat.
 	 */
 	vips_image_set_int( out, "pdf-n_pages", pdf->n_pages ); 
@@ -308,6 +303,11 @@ vips_foreign_load_pdf_set_image( VipsForeignLoadPdf *pdf, VipsImage *out )
 		4, VIPS_FORMAT_UCHAR,
 		VIPS_CODING_NONE, VIPS_INTERPRETATION_sRGB, res, res );
 
+        /* We render to a tilecache, so it has to be SMALLTILE.
+         */
+        if( vips_image_pipelinev( out, VIPS_DEMAND_STYLE_SMALLTILE, NULL ) )
+		return( -1 );
+
 	return( 0 );
 }
 

libvips/foreign/svgload.c

@@ -543,10 +543,9 @@ vips_foreign_load_svg_parse( VipsForeignLoadSvg *svg, VipsImage *out )
 		4, VIPS_FORMAT_UCHAR,
 		VIPS_CODING_NONE, VIPS_INTERPRETATION_sRGB, res, res );
 
-	/* We render to a cache with a couple of rows of tiles, so fat strips 
+	/* We use a tilecache, so it's smalltile.
-	 * work well.
 	 */
-        if( vips_image_pipelinev( out, VIPS_DEMAND_STYLE_FATSTRIP, NULL ) )
+        if( vips_image_pipelinev( out, VIPS_DEMAND_STYLE_SMALLTILE, NULL ) )
 		return( -1 );
 
 	return( 0 );

libvips/foreign/vipspng.c

@@ -393,7 +393,6 @@ png2vips_header( Read *read, VipsImage *out )
 	png_uint_32 width, height;
 	int bitdepth, color_type;
 	int interlace_type;
-	VipsDemandStyle hint;
 
 	png_uint_32 res_x, res_y;
 	int unit_type;
@@ -524,17 +523,7 @@ png2vips_header( Read *read, VipsImage *out )
 	VIPS_SETSTR( out->filename, 
 		vips_connection_filename( VIPS_CONNECTION( read->source ) ) );
 
-	/* Uninterlaced images will be read in seq mode. Interlaced images are
+	if( vips_image_pipelinev( out, VIPS_DEMAND_STYLE_THINSTRIP, NULL ) )
-	 * read via a huge memory buffer.
-	 */
-	if( interlace_type == PNG_INTERLACE_NONE ) 
-		/* Sequential mode needs thinstrip to work with things like
-		 * vips_shrink().
-		 */
-		hint = VIPS_DEMAND_STYLE_THINSTRIP;
-	else 
-		hint = VIPS_DEMAND_STYLE_ANY;
-	if( vips_image_pipelinev( out, hint, NULL ) )
 		return( -1 );
 
 	/* Fetch the ICC profile. @name is useless, something like "icc" or