fix background byte ordering in PDF

jcupitt · jcupitt · commit aa5abf3e7e3d · 2022-05-16T14:28:53.000+01:00
the `background` param was BGRA rather than vips-style RGBA see #2804
diff --git a/libvips/foreign/cairo.c b/libvips/foreign/cairo.c
@@ -69,6 +69,41 @@ vips__premultiplied_bgra2rgba( guint32 * restrict p, int n )
 	}
 }
 
+/* Unpremultiplied RGBA (vips convention) to cairo-style premul BGRA.
+ */
+void
+vips__rgba2bgra_premultiplied( guint32 * restrict p, int n )
+{
+	int x;
+
+	for( x = 0; x < n; x++ ) {
+		guint32 rgba = GUINT32_FROM_BE( p[x] );
+		guint8 a = rgba & 0xff;
+
+                guint32 bgra;
+
+                if( a == 0 )
+			bgra = 0;
+		else if( a == 255 )
+			bgra = (rgba & 0x00ff00ff) |
+				(rgba & 0x0000ff00) << 16 |
+				(rgba & 0xff000000) >> 16;
+                else {
+			int r = (rgba >> 24) & 0xff;
+			int g = (rgba >> 16) & 0xff;
+			int b = (rgba >> 8) & 0xff;
+
+			r = ((r * a) + 128) >> 8;
+			g = ((g * a) + 128) >> 8;
+			b = ((b * a) + 128) >> 8;
+
+                        bgra = (b << 24) | (g << 16) | (r << 8) | a;
+		}
+
+                p[x] = GUINT32_TO_BE( bgra );
+	}
+}
+
 /* Convert from PDFium-style BGRA to RGBA.
  */
 void
diff --git a/libvips/foreign/pdfiumload.c b/libvips/foreign/pdfiumload.c
@@ -524,6 +524,10 @@ vips_foreign_load_pdf_header( VipsForeignLoad *load )
 		VIPS_AREA( pdf->background )->n )) )
 		return( -1 );
 
+	/* Swap B and R.
+	 */
+	vips__bgra2rgba( (guint32 *) pdf->ink, 1 ); 
+
 	return( 0 );
 }
 
@@ -572,10 +576,10 @@ vips_foreign_load_pdf_generate( VipsRegion *or,
 		if( vips_foreign_load_pdf_get_page( pdf, pdf->page_no + i ) )
 			return( -1 ); 
 
-		/* 4 means RGBA.
-		 */
 		g_mutex_lock( vips_pdfium_mutex );
 
+		/* 4 means RGBA.
+		 */
 		bitmap = FPDFBitmap_CreateEx( rect.width, rect.height, 4, 
 			VIPS_REGION_ADDR( or, rect.left, rect.top ), 
 			VIPS_REGION_LSKIP( or ) );  
diff --git a/libvips/foreign/popplerload.c b/libvips/foreign/popplerload.c
@@ -380,16 +380,17 @@ vips_foreign_load_pdf_header( VipsForeignLoad *load )
 	vips_foreign_load_pdf_set_image( pdf, load->out ); 
 
 	/* Convert the background to the image format. 
-	 *
-	 * FIXME ... we probably should convert this to pre-multiplied BGRA
-	 * to match the Cairo convention. See vips__premultiplied_bgra2rgba().
 	 */
 	if( !(pdf->ink = vips__vector_to_ink( class->nickname, 
 		load->out, 
 		VIPS_AREA( pdf->background )->data, NULL, 
 		VIPS_AREA( pdf->background )->n )) )
 		return( -1 );
 
+	/* Swap to cairo-style premultiplied bgra.
+	 */
+	vips__rgba2bgra_premultiplied( (guint32 *) pdf->ink, 1 ); 
+
 	vips_source_minimise( pdf->source );
 
 	return( 0 );
diff --git a/libvips/include/vips/internal.h b/libvips/include/vips/internal.h
@@ -325,6 +325,8 @@ char *vips__xml_properties( VipsImage *image );
  */
 VIPS_API
 void vips__premultiplied_bgra2rgba( guint32 * restrict p, int n );
+VIPS_API
+void vips__rgba2bgra_premultiplied( guint32 * restrict p, int n );
 void vips__bgra2rgba( guint32 * restrict p, int n );
 void vips__Lab2LabQ_vec( VipsPel *out, float *in, int width );
 void vips__LabQ2Lab_vec( float *out, VipsPel *in, int width );
