feat(#60): support zero top and left params in extract operation

image.go

@@ -48,6 +48,11 @@ func (i *Image) Extract(top, left, width, height int) ([]byte, error) {
 		AreaWidth:  width,
 		AreaHeight: height,
 	}
+
+	if top == 0 && left == 0 {
+		options.Top = -1
+	}
+
 	return i.Process(options)
 }
 

image_test.go

@@ -48,6 +48,20 @@ func TestImageExtract(t *testing.T) {
 	Write("fixtures/test_extract_out.jpg", buf)
 }
 
+func TestImageExtractZero(t *testing.T) {
+	buf, err := initImage("test.jpg").Extract(0, 0, 300, 200)
+	if err != nil {
+		t.Errorf("Cannot process the image: %s", err)
+	}
+
+	err = assertSize(buf, 300, 200)
+	if err != nil {
+		t.Error(err)
+	}
+
+	Write("fixtures/test_extract_zero_out.jpg", buf)
+}
+
 func TestImageEnlarge(t *testing.T) {
 	buf, err := initImage("test.png").Enlarge(500, 375)
 	if err != nil {

resize.go

@@ -229,7 +229,7 @@ func extractOrEmbedImage(image *C.VipsImage, o Options) (*C.VipsImage, error) {
 		left, top := (o.Width-inWidth)/2, (o.Height-inHeight)/2
 		image, err = vipsEmbed(image, left, top, o.Width, o.Height, o.Extend)
 		break
-	case o.Top > 0 || o.Left > 0:
+	case o.Top != 0 || o.Left != 0:
 		if o.AreaWidth == 0 {
 			o.AreaHeight = o.Width
 		}

vips.go

@@ -8,6 +8,7 @@ import "C"
 
 import (
 	"errors"
+	"math"
 	"os"
 	"runtime"
 	"strings"
@@ -340,6 +341,10 @@ func vipsSave(image *C.VipsImage, o vipsSaveOptions) ([]byte, error) {
 	return buf, nil
 }
 
+func max(x int) int {
+	return int(math.Max(float64(x), 0))
+}
+
 func vipsExtract(image *C.VipsImage, left, top, width, height int) (*C.VipsImage, error) {
 	var buf *C.VipsImage
 	defer C.g_object_unref(C.gpointer(image))
@@ -348,6 +353,7 @@ func vipsExtract(image *C.VipsImage, left, top, width, height int) (*C.VipsImage
 		return nil, errors.New("Maximum image size exceeded")
 	}
 
+	top, left = max(top), max(left)
 	err := C.vips_extract_area_bridge(image, &buf, C.int(left), C.int(top), C.int(width), C.int(height))
 	if err != 0 {
 		return nil, catchVipsError()