Expose routines for reading and creating .png files

src/Libs/cairo-1.0/Internal/ImageSurface.cs

@@ -25,4 +25,7 @@ public class ImageSurface
 
     [DllImport(CairoImportResolver.Library, EntryPoint = "cairo_image_surface_get_width")]
     public static extern int GetWidth(SurfaceHandle handle);
+
+    [DllImport(CairoImportResolver.Library, EntryPoint = "cairo_image_surface_create_from_png")]
+    public static extern SurfaceOwnedHandle CreateFromPng(GLib.Internal.NonNullableUtf8StringOwnedHandle filename);
 }

src/Libs/cairo-1.0/Internal/Surface.cs

@@ -64,4 +64,9 @@ public partial class Surface
 
     [DllImport(CairoImportResolver.Library, EntryPoint = "cairo_surface_status")]
     public static extern Status Status(SurfaceHandle handle);
+
+    [DllImport(CairoImportResolver.Library, EntryPoint = "cairo_surface_write_to_png")]
+    public static extern Status WriteToPng(SurfaceHandle handle, GLib.Internal.NonNullableUtf8StringOwnedHandle filename);
+
+
 }

src/Libs/cairo-1.0/Public/ImageSurface.cs

@@ -45,5 +45,11 @@ public Span<byte> GetData()
             return new Span<byte>(data.ToPointer(), GetSizeInBytes());
         }
     }
+
+    public static Surface CreateFromPng(string filename)
+    {
+        using var filenameNative = GLib.Internal.NonNullableUtf8StringOwnedHandle.Create(filename);
+        return new Surface(Internal.ImageSurface.CreateFromPng(filenameNative));
+    }
 }
 

src/Libs/cairo-1.0/Public/Surface.cs

@@ -86,4 +86,10 @@ public void MarkDirty(int x, int y, int width, int height)
             ? null
             : new Device(deviceHandle.OwnedCopy());
     }
+
+    public Status WriteToPng(string filename)
+    {
+        using var filenameNative = GLib.Internal.NonNullableUtf8StringOwnedHandle.Create(filename);
+        return Internal.Surface.WriteToPng(Handle, filenameNative);
+    }
 }