Merge pull request #226 from cshum/feature/getpoint

GetPoint method

vips/arithmetic.c

@@ -45,3 +45,7 @@ int find_trim(VipsImage *in, int *left, int *top, int *width, int *height,
   vips_area_unref(VIPS_AREA(vipsBackground));
   return code;
 }
+
+int getpoint(VipsImage *in, double **vector, int n, int x, int y) {
+  return vips_getpoint(in, vector, &n, x, y, NULL);
+}

vips/arithmetic.go

@@ -2,6 +2,7 @@ package vips
 
 // #include "arithmetic.h"
 import "C"
+import "unsafe"
 
 // https://libvips.github.io/libvips/API/current/libvips-arithmetic.html#vips-add
 func vipsAdd(left *C.VipsImage, right *C.VipsImage) (*C.VipsImage, error) {
@@ -99,3 +100,17 @@ func vipsFindTrim(in *C.VipsImage, threshold float64, backgroundColor *Color) (i
 
 	return int(left), int(top), int(width), int(height), nil
 }
+
+// https://libvips.github.io/libvips/API/current/libvips-arithmetic.html#vips-getpoint
+func vipsGetPoint(in *C.VipsImage, n int, x int, y int) ([]float64, error) {
+	incOpCounter("getpoint")
+	var out *C.double
+	defer gFreePointer(unsafe.Pointer(out))
+
+	if err := C.getpoint(in, &out, C.int(n), C.int(x), C.int(y)); err != 0 {
+		return nil, handleVipsError()
+	}
+
+	// maximum n is 4
+	return (*[4]float64)(unsafe.Pointer(out))[:n:n], nil
+}

vips/arithmetic.h

@@ -12,3 +12,4 @@ int invert_image(VipsImage *in, VipsImage **out);
 int average(VipsImage *in, double *out);
 int find_trim(VipsImage *in, int *left, int *top, int *width, int *height,
               double threshold, double r, double g, double b);
+int getpoint(VipsImage *in, double **vector, int n, int x, int y);

vips/image.go

@@ -1272,6 +1272,16 @@ func (r *ImageRef) FindTrim(threshold float64, backgroundColor *Color) (int, int
 	return vipsFindTrim(r.image, threshold, backgroundColor)
 }
 
+// GetPoint reads a single pixel on an image.
+// The pixel values are returned in a slice of length n.
+func (r *ImageRef) GetPoint(x int, y int) ([]float64, error) {
+	n := 3
+	if vipsHasAlpha(r.image) {
+		n = 4
+	}
+	return vipsGetPoint(r.image, n, x, y)
+}
+
 // DrawRect draws an (optionally filled) rectangle with a single colour
 func (r *ImageRef) DrawRect(ink ColorRGBA, left int, top int, width int, height int, fill bool) error {
 	err := vipsDrawRect(r.image, ink, left, top, width, height, fill)

vips/image_golden_test.go

@@ -446,6 +446,73 @@ func TestImage_Rank(t *testing.T) {
 	}, nil, nil)
 }
 
+func TestImage_GetPointWhite(t *testing.T) {
+	goldenTest(t, resources+"png-24bit.png", func(img *ImageRef) error {
+		point, err := img.GetPoint(10, 10)
+
+		assert.Equal(t, 3, len(point))
+		assert.Equal(t, 255.0, point[0])
+		assert.Equal(t, 255.0, point[1])
+		assert.Equal(t, 255.0, point[2])
+
+		return err
+	}, nil, nil)
+}
+
+func TestImage_GetPointYellow(t *testing.T) {
+	goldenTest(t, resources+"png-24bit.png", func(img *ImageRef) error {
+		point, err := img.GetPoint(400, 10)
+
+		assert.Equal(t, 3, len(point))
+		assert.Equal(t, 255.0, point[0])
+		assert.Equal(t, 255.0, point[1])
+		assert.Equal(t, 0.0, point[2])
+
+		return err
+	}, nil, nil)
+}
+
+func TestImage_GetPointWhiteR(t *testing.T) {
+	goldenTest(t, resources+"png-24bit.png", func(img *ImageRef) error {
+		point, err := img.GetPoint(10, 10)
+
+		assert.Equal(t, 3, len(point))
+		assert.Equal(t, 255.0, point[0])
+		assert.Equal(t, 255.0, point[1])
+		assert.Equal(t, 255.0, point[2])
+
+		return err
+	}, nil, nil)
+}
+
+func TestImage_GetPoint_WithAlpha(t *testing.T) {
+	goldenTest(t, resources+"with_alpha.png", func(img *ImageRef) error {
+		point, err := img.GetPoint(10, 10)
+
+		assert.Equal(t, 4, len(point))
+		assert.Equal(t, 0.0, point[0])
+		assert.Equal(t, 0.0, point[1])
+		assert.Equal(t, 0.0, point[2])
+		assert.Equal(t, 255.0, point[3])
+
+		return err
+	}, nil, nil)
+}
+
+func TestImage_GetPoint_WithAlpha2(t *testing.T) {
+	goldenTest(t, resources+"with_alpha.png", func(img *ImageRef) error {
+		point, err := img.GetPoint(0, 0)
+
+		assert.Equal(t, 4, len(point))
+		assert.Equal(t, 0.0, point[0])
+		assert.Equal(t, 0.0, point[1])
+		assert.Equal(t, 0.0, point[2])
+		assert.Equal(t, 0.0, point[3])
+
+		return err
+	}, nil, nil)
+}
+
 func TestImage_SimilarityRGB(t *testing.T) {
 	goldenTest(t, resources+"jpg-24bit.jpg", func(img *ImageRef) error {
 		return img.Similarity(0.5, 5, &ColorRGBA{R: 127, G: 127, B: 127, A: 127},