support rsvg_handle_get_intrinsic_size_in_pixels

librsvg 2.52+ has this new bit of API for finding the SVG dimensions

.gitignore

@@ -1,4 +1,6 @@
-compile
+release
+build
+debug
 .pytest_cache
 .dirstamp
 a.out
@@ -29,8 +31,6 @@ tags
 *.o
 *.a
 fuzz/*_fuzzer
-Vips-8.0.gir
-Vips-8.0.typelib
 .*.swp
 *.lo
 *.bak

libvips/foreign/svgload.c

@@ -24,6 +24,8 @@
  * 	- librsvg can no longer render very large images :( 
  * 14/10/21
  * 	- allow utf-8 headers for svg detection
+ * 28/4/22
+ * 	- support rsvg_handle_get_intrinsic_size_in_pixels()
  */
 
 /*
@@ -317,8 +319,75 @@ vips_foreign_load_svg_get_flags( VipsForeignLoad *load )
 	return( VIPS_FOREIGN_SEQUENTIAL );
 }
 
+#ifdef HAVE_RSVG_HANDLE_GET_INTRINSIC_SIZE_IN_PIXELS
+
 static int
-vips_foreign_load_svg_parse( VipsForeignLoadSvg *svg, VipsImage *out )
+vips_foreign_load_svg_get_size( VipsForeignLoadSvg *svg, 
+	int *out_width, int *out_height )
+{
+	VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( svg );
+
+	double width;
+	double height;
+	double scale;
+
+	/* If the SVG does not define a width or height we will fall back to
+	 * this size. The SVG will be rendered to fit this viewport
+	 * by rsvg_handle_render_document() below.
+	 */
+	width = 1928;
+	height = 1080;
+
+	/* Get dimensions with the default scale.
+	 */
+	rsvg_handle_set_dpi( svg->page, 72.0 );
+	rsvg_handle_get_intrinsic_size_in_pixels( svg->page, &width, &height );
+	if( width <= 0 || height <= 0 ) {
+		vips_error( class->nickname, "%s", _( "bad dimensions" ) );
+		return( -1 );
+	}
+
+	/* Calculate dimensions at required dpi/scale.
+	 */
+	scale = svg->scale * svg->dpi / 72.0;
+	if( scale != 1.0 ) {
+		double scaled_width;
+		double scaled_height;
+
+		rsvg_handle_set_dpi( svg->page, svg->dpi * svg->scale );
+		rsvg_handle_get_intrinsic_size_in_pixels( svg->page, 
+			&scaled_width, &scaled_height );
+
+		if( scaled_width == width &&
+			scaled_height == height ) {
+			/* SVG without width and height always reports the same 
+			 * dimensions regardless of dpi. Apply dpi/scale using 
+			 * cairo instead.
+			 */
+			svg->cairo_scale = scale;
+			width = width * scale;
+			height = height * scale;
+		} 
+		else {
+			/* SVG with width and height reports correctly scaled 
+			 * dimensions.
+			 */
+			width = scaled_width;
+			height = scaled_height;
+		}
+	}
+
+	*out_width = VIPS_ROUND_UINT( width );
+	*out_height = VIPS_ROUND_UINT( height );
+
+	return ( 0 );
+}
+
+#else /*!HAVE_RSVG_HANDLE_GET_INTRINSIC_SIZE_IN_PIXELS*/
+
+static int
+vips_foreign_load_svg_get_size( VipsForeignLoadSvg *svg, 
+	int *out_width, int *out_height )
 {
 	VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( svg );
 
@@ -326,7 +395,6 @@ vips_foreign_load_svg_parse( VipsForeignLoadSvg *svg, VipsImage *out )
 	int width;
 	int height;
 	double scale;
-	double res;
 
 	/* Calculate dimensions at default dpi/scale.
 	 */
@@ -366,6 +434,24 @@ vips_foreign_load_svg_parse( VipsForeignLoadSvg *svg, VipsImage *out )
 		}
 	}
 
+	*out_width = width;
+	*out_height = height;
+
+	return ( 0 );
+}
+
+#endif/*HAVE_RSVG_HANDLE_GET_INTRINSIC_SIZE_IN_PIXELS*/
+
+static int
+vips_foreign_load_svg_parse( VipsForeignLoadSvg *svg, VipsImage *out )
+{
+	int width;
+	int height;
+	double res;
+
+	if( vips_foreign_load_svg_get_size( svg, &width, &height ) )
+		return( -1 );
+
 	/* We need pixels/mm for vips.
 	 */
 	res = svg->dpi / 25.4;

meson.build

@@ -354,6 +354,10 @@ if librsvg_dep.found() and cairo_dep.found()
     if librsvg_dep.version().version_compare('>=2.46')
         cfg_var.set('HAVE_RSVG_HANDLE_RENDER_DOCUMENT', '1')
     endif
+    # 2.56 for rsvg_handle_get_intrinsic_size_in_pixels
+    if librsvg_dep.version().version_compare('>=2.52')
+        cfg_var.set('HAVE_RSVG_HANDLE_GET_INTRINSIC_SIZE_IN_PIXELS', '1')
+    endif
 endif
 
 openslide_dep = dependency('openslide', version: '>=3.3.0', required: get_option('openslide'))