Add read_ptr method to Vips::Image

Author: ankane

lib/vips/image.rb

@@ -1235,10 +1235,20 @@ def to_a
       to_enum.to_a
     end
 
+    # Return a read-only pointer to the pixel data, if possible.
+    #
+    # @return [FFI::Pointer] pointer to the pixel data
+    def read_ptr
+      copy = copy_memory
+      ptr = copy.unsafe_data_ptr
+      ptr.instance_variable_set(:@_vips_reference, copy)
+      ptr
+    end
+
     # Return a pointer to the pixel data, if possible.
     #
     # @return [FFI::Pointer] pointer to the pixel data
-    def data_ptr
+    def unsafe_data_ptr
       ptr = Vips.vips_image_get_data self
       raise Vips::Error if ptr.null?
 

spec/image_spec.rb

@@ -127,9 +127,9 @@
     expect { Vips::Image.new_from_memory_copy(data, 16, 16, 1, :uchar) }.to raise_error(Vips::Error)
   end
 
-  it "can load an image from a data pointer" do
+  it "can load an image from a read pointer" do
     image = Vips::Image.black(16, 16) + 128
-    data = image.data_ptr
+    data = image.read_ptr
     expect(data).to be_a(FFI::Pointer)
     expect(data.size).to eq(1024)