Function signature changed again, no need for multiple return value

README.md

@@ -21,7 +21,8 @@ Import package with
 import "github.com/nfnt/resize"
 ```
 
-Resize creates a scaled image with new dimensions (width, height) using the interpolation function interp.
+Resize creates a scaled image with new dimensions (`width`, `height`) using the interpolation function interp.
+If either `width` or `height` is set to 0, it will be set to an aspect ratio preserving value.
 
 ```go
 resize.Resize(width, height int, img image.Image, interp resize.InterpolationFunction) image.Image, error 
@@ -60,10 +61,8 @@ func main() {
 	file.Close()
 
 	// resize to width 1000 using Lanczos resampling
-	m, err := resize.Resize(1000, -1, img, resize.Lanczos3)
-	if err != nil {
-		return
-	}
+	// and preserve aspect ration
+	m := resize.Resize(1000, 0, img, resize.Lanczos3)
 
 	out, err := os.Create("test_resized.jpg")
 	if err != nil {

resize.go

@@ -25,7 +25,6 @@ THIS SOFTWARE.
 package resize
 
 import (
-	"errors"
 	"image"
 	"image/color"
 	"runtime"
@@ -47,9 +46,9 @@ func (t *Trans2) Eval(x, y float32) (u, v float32) {
 }
 
 // Calculate scaling factors using old and new image dimensions.
-func calcFactors(width, height int, oldWidth, oldHeight float32) (scaleX, scaleY float32) {
-	if width == -1 {
-		if height == -1 {
+func calcFactors(width, height uint, oldWidth, oldHeight float32) (scaleX, scaleY float32) {
+	if width == 0 {
+		if height == 0 {
 			scaleX = 1.0
 			scaleY = 1.0
 		} else {
@@ -58,7 +57,7 @@ func calcFactors(width, height int, oldWidth, oldHeight float32) (scaleX, scaleY
 		}
 	} else {
 		scaleX = oldWidth / float32(width)
-		if height == -1 {
+		if height == 0 {
 			scaleY = scaleX
 		} else {
 			scaleY = oldHeight / float32(height)
@@ -73,14 +72,10 @@ type InterpolationFunction func(float32, float32, image.Image) color.RGBA64
 
 // Resize an image to new width w and height h using the interpolation function interp.
 // A new image with the given dimensions will be returned.
-// If one of the parameters w or h is set to -1, its size will be calculated so that
+// If one of the parameters w or h is set to 0, its size will be calculated so that
 // the aspect ratio is that of the originating image.
 // The resizing algorithm uses channels for parallel computation.
-func Resize(width, height int, img image.Image, interp InterpolationFunction) (out image.Image, err error) {
-	if width < -1 || height < -1 {
-		err = errors.New("Wrong width/height argument")
-		return
-	}
+func Resize(width, height uint, img image.Image, interp InterpolationFunction) image.Image {
 	oldBounds := img.Bounds()
 	oldWidth := float32(oldBounds.Dx())
 	oldHeight := float32(oldBounds.Dy())
@@ -108,7 +103,6 @@ func Resize(width, height int, img image.Image, interp InterpolationFunction) (o
 	for i := 0; i < NCPU; i++ {
 		<-c
 	}
-	out = m
 
-	return
+	return m
 }

resize_test.go

@@ -11,30 +11,23 @@ var img = image.NewGray16(image.Rect(0, 0, 3, 3))
 func Test_Nearest(t *testing.T) {
 	img.Set(1, 1, color.White)
 
-	m, err := Resize(6, -1, img, NearestNeighbor)
+	m := Resize(6, 0, img, NearestNeighbor)
 
-	if err != nil || m.At(2, 2) != m.At(3, 3) {
+	if m.At(2, 2) != m.At(3, 3) {
 		t.Fail()
 	}
 }
 
 func Test_Param1(t *testing.T) {
-	m, err := Resize(-1, -1, img, NearestNeighbor)
-	if err != nil || m.Bounds() != img.Bounds() {
+	m := Resize(0, 0, img, NearestNeighbor)
+	if m.Bounds() != img.Bounds() {
 		t.Fail()
 	}
 }
 
 func Test_Param2(t *testing.T) {
-	_, err := Resize(-100, -1, img, NearestNeighbor)
-	if err == nil {
-		t.Fail()
-	}
-}
-
-func Test_Param3(t *testing.T) {
-	m, err := Resize(0, -1, img, NearestNeighbor)
-	if err != nil || m.Bounds() != image.Rect(0, 0, 0, 0) {
+	m := Resize(100, 0, img, NearestNeighbor)
+	if m.Bounds() != image.Rect(0, 0, 100, 100) {
 		t.Fail()
 	}
 }
@@ -42,8 +35,8 @@ func Test_Param3(t *testing.T) {
 func Test_ZeroImg(t *testing.T) {
 	zeroImg := image.NewGray16(image.Rect(0, 0, 0, 0))
 
-	m, err := Resize(-1, -1, zeroImg, NearestNeighbor)
-	if err != nil || m.Bounds() != zeroImg.Bounds() {
+	m := Resize(0, 0, zeroImg, NearestNeighbor)
+	if m.Bounds() != zeroImg.Bounds() {
 		t.Fail()
 	}
 }