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* feature(thumbnails): add the ability to define custom image processors * fix(ci): add exported member comment * docs(thumbnails): mention processors in readme * fix: codacy and code review feedback * fix: thumbnail readme markdown Co-authored-by: Martin <github@diemattels.at> --------- Co-authored-by: Martin <github@diemattels.at>
86 lines
2.3 KiB
Go
86 lines
2.3 KiB
Go
package thumbnail
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import (
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"image"
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"image/color"
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"image/draw"
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"image/gif"
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"strings"
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"github.com/disintegration/imaging"
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)
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// Generator generates a web friendly file version.
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type Generator interface {
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Generate(image.Rectangle, interface{}, Processor) (interface{}, error)
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}
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// SimpleGenerator is the default image generator and is used for all image types expect gif.
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type SimpleGenerator struct{}
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// Generate generates a alternative image version.
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func (g SimpleGenerator) Generate(size image.Rectangle, img interface{}, processor Processor) (interface{}, error) {
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m, ok := img.(image.Image)
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if !ok {
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return nil, ErrInvalidType
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}
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return processor.Process(m, size.Dx(), size.Dy(), imaging.Lanczos), nil
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}
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// GifGenerator is used to create a web friendly version of the provided gif image.
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type GifGenerator struct{}
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// Generate generates a alternative gif version.
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func (g GifGenerator) Generate(size image.Rectangle, img interface{}, processor Processor) (interface{}, error) {
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// Code inspired by https://github.com/willnorris/gifresize/blob/db93a7e1dcb1c279f7eeb99cc6d90b9e2e23e871/gifresize.go
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m, ok := img.(*gif.GIF)
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if !ok {
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return nil, ErrInvalidType
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}
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// Create a new RGBA image to hold the incremental frames.
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srcX, srcY := m.Config.Width, m.Config.Height
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b := image.Rect(0, 0, srcX, srcY)
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tmp := image.NewRGBA(b)
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for i, frame := range m.Image {
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bounds := frame.Bounds()
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prev := tmp
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draw.Draw(tmp, bounds, frame, bounds.Min, draw.Over)
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processed := processor.Process(tmp, size.Dx(), size.Dy(), imaging.Lanczos)
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m.Image[i] = g.imageToPaletted(processed, frame.Palette)
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switch m.Disposal[i] {
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case gif.DisposalBackground:
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tmp = image.NewRGBA(b)
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case gif.DisposalPrevious:
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tmp = prev
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}
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}
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m.Config.Width = size.Dx()
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m.Config.Height = size.Dy()
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return m, nil
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}
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func (g GifGenerator) imageToPaletted(img image.Image, p color.Palette) *image.Paletted {
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b := img.Bounds()
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pm := image.NewPaletted(b, p)
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draw.FloydSteinberg.Draw(pm, b, img, image.Point{})
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return pm
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}
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// GeneratorForType returns the generator for a given file type
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// or nil if the type is not supported.
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func GeneratorForType(fileType string) (Generator, error) {
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switch strings.ToLower(fileType) {
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case typePng, typeJpg, typeJpeg:
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return SimpleGenerator{}, nil
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case typeGif:
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return GifGenerator{}, nil
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default:
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return nil, ErrNoEncoderForType
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}
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}
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