Image resource refactor

This commit pulls most of the image related logic into its own package, to make it easier to reason about and extend.

This is also a rewrite of the transformation logic used in Hugo Pipes, mostly to allow constructs like the one below:

    {{ ($myimg | fingerprint ).Width }}

Fixes #5903
Fixes #6234
Fixes #6266

resources/images/image.go

@@ -0,0 +1,170 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package images
+
+import (
+	"image"
+	"image/jpeg"
+	"io"
+	"sync"
+
+	"github.com/disintegration/imaging"
+	"github.com/gohugoio/hugo/common/hugio"
+	"github.com/pkg/errors"
+)
+
+func NewImage(f imaging.Format, proc *ImageProcessor, img image.Image, s Spec) *Image {
+	if img != nil {
+		return &Image{
+			Format: f,
+			Proc:   proc,
+			Spec:   s,
+			imageConfig: &imageConfig{
+				config:       imageConfigFromImage(img),
+				configLoaded: true,
+			},
+		}
+	}
+	return &Image{Format: f, Proc: proc, Spec: s, imageConfig: &imageConfig{}}
+}
+
+type Image struct {
+	Format imaging.Format
+
+	Proc *ImageProcessor
+
+	Spec Spec
+
+	*imageConfig
+}
+
+func (i *Image) EncodeTo(conf ImageConfig, img image.Image, w io.Writer) error {
+	switch i.Format {
+	case imaging.JPEG:
+
+		var rgba *image.RGBA
+		quality := conf.Quality
+
+		if nrgba, ok := img.(*image.NRGBA); ok {
+			if nrgba.Opaque() {
+				rgba = &image.RGBA{
+					Pix:    nrgba.Pix,
+					Stride: nrgba.Stride,
+					Rect:   nrgba.Rect,
+				}
+			}
+		}
+		if rgba != nil {
+			return jpeg.Encode(w, rgba, &jpeg.Options{Quality: quality})
+		}
+		return jpeg.Encode(w, img, &jpeg.Options{Quality: quality})
+	default:
+		return imaging.Encode(w, img, i.Format)
+	}
+}
+
+// Height returns i's height.
+func (i *Image) Height() int {
+	i.initConfig()
+	return i.config.Height
+}
+
+// Width returns i's width.
+func (i *Image) Width() int {
+	i.initConfig()
+	return i.config.Width
+}
+
+func (i Image) WithImage(img image.Image) *Image {
+	i.Spec = nil
+	i.imageConfig = &imageConfig{
+		config:       imageConfigFromImage(img),
+		configLoaded: true,
+	}
+
+	return &i
+}
+
+func (i Image) WithSpec(s Spec) *Image {
+	i.Spec = s
+	i.imageConfig = &imageConfig{}
+	return &i
+}
+
+func (i *Image) initConfig() error {
+	var err error
+	i.configInit.Do(func() {
+		if i.configLoaded {
+			return
+		}
+
+		var (
+			f      hugio.ReadSeekCloser
+			config image.Config
+		)
+
+		f, err = i.Spec.ReadSeekCloser()
+		if err != nil {
+			return
+		}
+		defer f.Close()
+
+		config, _, err = image.DecodeConfig(f)
+		if err != nil {
+			return
+		}
+		i.config = config
+	})
+
+	if err != nil {
+		return errors.Wrap(err, "failed to load image config")
+	}
+
+	return nil
+}
+
+type ImageProcessor struct {
+	Cfg Imaging
+}
+
+func (p *ImageProcessor) Fill(src image.Image, conf ImageConfig) (image.Image, error) {
+	if conf.AnchorStr == SmartCropIdentifier {
+		return smartCrop(src, conf.Width, conf.Height, conf.Anchor, conf.Filter)
+	}
+	return imaging.Fill(src, conf.Width, conf.Height, conf.Anchor, conf.Filter), nil
+}
+
+func (p *ImageProcessor) Fit(src image.Image, conf ImageConfig) (image.Image, error) {
+	return imaging.Fit(src, conf.Width, conf.Height, conf.Filter), nil
+}
+
+func (p *ImageProcessor) Resize(src image.Image, conf ImageConfig) (image.Image, error) {
+	return imaging.Resize(src, conf.Width, conf.Height, conf.Filter), nil
+}
+
+type Spec interface {
+	// Loads the image source.
+	ReadSeekCloser() (hugio.ReadSeekCloser, error)
+}
+
+type imageConfig struct {
+	config       image.Config
+	configInit   sync.Once
+	configLoaded bool
+}
+
+func imageConfigFromImage(img image.Image) image.Config {
+	b := img.Bounds()
+	return image.Config{Width: b.Max.X, Height: b.Max.Y}
+}