parse crop and resize params before transforms

transform.go

@@ -251,12 +251,18 @@ func exifOrientation(r io.Reader) (opt Options) {
 // transformImage modifies the image m based on the transformations specified
 // in opt.
 func transformImage(m image.Image, opt Options) image.Image {
+	// Parse crop and resize parameters before applying any transforms.
+	// This is to ensure that any percentage-based values are based off the
+	// size of the original image.
+	rect := cropParams(m, opt)
+	w, h, resize := resizeParams(m, opt)
+
 	// crop if needed
-	if r := cropParams(m, opt); !m.Bounds().Eq(r) {
+	if !m.Bounds().Eq(rect) {
-		m = imaging.Crop(m, r)
+		m = imaging.Crop(m, rect)
 	}
 	// resize if needed
-	if w, h, ok := resizeParams(m, opt); ok {
+	if resize {
 		if opt.Fit {
 			m = imaging.Fit(m, w, h, resampleFilter)
 		} else {

transform_test.go

@@ -351,6 +351,13 @@ func TestTransformImage(t *testing.T) {
 			Options{CropHeight: 2, CropWidth: 2, CropX: 2, CropY: 2},
 			newImage(2, 2, yellow, yellow, yellow, yellow),
 		},
+
+		// percentage-based resize in addition to rectangular crop
+		{
+			newImage(12, 12, red),
+			Options{Width: 0.5, Height: 0.5, CropWidth: 8, CropHeight: 8},
+			newImage(6, 6, red),
+		},
 	}
 
 	for _, tt := range tests {