Add read_ptr method to Vips::Image

Author: ankane

Diff for: lib/vips/image.rb

@@ -41,6 +41,10 @@ module Vips
   attach_function :vips_image_get_height, [:pointer], :int
   attach_function :vips_image_get_bands, [:pointer], :int
 
+  enum :vips_band_format, [:notset, -1, :uchar, :char, :ushort, :short, :uint, :int, :float, :complex, :double, :dpcomplex]
+  attach_function :vips_format_sizeof, [:vips_band_format], :int64
+  attach_function :vips_image_get_data, [:pointer], :pointer
+
   if Vips.at_least_libvips?(8, 5)
     attach_function :vips_image_get_fields, [:pointer], :pointer
     attach_function :vips_image_hasalpha, [:pointer], :int
@@ -1231,6 +1235,19 @@ 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 = Vips.vips_image_get_data copy
+      raise Vips::Error if ptr.null?
+
+      ptr.instance_variable_set(:@vips_reference, copy)
+
+      ptr.slice(0, width * height * bands * Vips.vips_format_sizeof(format))
+    end
+
     # Return the largest integral value not greater than the argument.
     #
     # @return [Image] floor of image

Diff for: spec/image_spec.rb

@@ -127,6 +127,21 @@
     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 read pointer" do
+    image = Vips::Image.black(16, 16) + 128
+    data = image.read_ptr
+    expect(data).to be_a(FFI::Pointer)
+    expect(data.size).to eq(1024)
+
+    x = Vips::Image.new_from_memory data,
+      image.width, image.height, image.bands, image.format
+
+    expect(x.width).to eq(16)
+    expect(x.height).to eq(16)
+    expect(x.bands).to eq(1)
+    expect(x.avg).to eq(128)
+  end
+
   if has_jpeg?
     it "can save an image to a buffer" do
       image = Vips::Image.black(16, 16) + 128