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* Crop avatar before resizing (#1268) Signed-off-by: Rob Watson <rfwatson@users.noreply.github.com> * Fix spelling error Signed-off-by: Rob Watson <rfwatson@users.noreply.github.com>
193 lines
5.1 KiB
Go
193 lines
5.1 KiB
Go
/*
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Package cutter provides a function to crop image.
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By default, the original image will be cropped at the
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given size from the top left corner.
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croppedImg, err := cutter.Crop(img, cutter.Config{
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Width: 250,
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Height: 500,
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})
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Most of the time, the cropped image will share some memory
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with the original, so it should be used read only. You must
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ask explicitely for a copy if nedded.
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croppedImg, err := cutter.Crop(img, cutter.Config{
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Width: 250,
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Height: 500,
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Options: Copy,
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})
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It is possible to specify the top left position:
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croppedImg, err := cutter.Crop(img, cutter.Config{
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Width: 250,
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Height: 500,
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Anchor: image.Point{100, 100},
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Mode: TopLeft, // optional, default value
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})
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The Anchor property can represents the center of the cropped image
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instead of the top left corner:
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croppedImg, err := cutter.Crop(img, cutter.Config{
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Width: 250,
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Height: 500,
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Mode: Centered,
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})
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The default crop use the specified dimension, but it is possible
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to use Width and Heigth as a ratio instead. In this case,
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the resulting image will be as big as possible to fit the asked ratio
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from the anchor position.
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croppedImg, err := cutter.Crop(baseImage, cutter.Config{
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Width: 4,
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Height: 3,
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Mode: Centered,
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Options: Ratio,
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})
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*/
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package cutter
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import (
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"image"
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"image/draw"
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)
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// Config is used to defined
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// the way the crop should be realized.
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type Config struct {
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Width, Height int
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Anchor image.Point // The Anchor Point in the source image
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Mode AnchorMode // Which point in the resulting image the Anchor Point is referring to
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Options Option
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}
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// AnchorMode is an enumeration of the position an anchor can represent.
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type AnchorMode int
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const (
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// TopLeft defines the Anchor Point
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// as the top left of the cropped picture.
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TopLeft AnchorMode = iota
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// Centered defines the Anchor Point
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// as the center of the cropped picture.
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Centered = iota
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)
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// Option flags to modify the way the crop is done.
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type Option int
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const (
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// Ratio flag is use when Width and Height
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// must be used to compute a ratio rather
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// than absolute size in pixels.
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Ratio Option = 1 << iota
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// Copy flag is used to enforce the function
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// to retrieve a copy of the selected pixels.
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// This disable the use of SubImage method
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// to compute the result.
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Copy = 1 << iota
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)
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// An interface that is
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// image.Image + SubImage method.
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type subImageSupported interface {
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SubImage(r image.Rectangle) image.Image
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}
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// Crop retrieves an image that is a
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// cropped copy of the original img.
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//
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// The crop is made given the informations provided in config.
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func Crop(img image.Image, c Config) (image.Image, error) {
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maxBounds := c.maxBounds(img.Bounds())
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size := c.computeSize(maxBounds, image.Point{c.Width, c.Height})
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cr := c.computedCropArea(img.Bounds(), size)
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cr = img.Bounds().Intersect(cr)
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if c.Options&Copy == Copy {
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return cropWithCopy(img, cr)
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}
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if dImg, ok := img.(subImageSupported); ok {
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return dImg.SubImage(cr), nil
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}
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return cropWithCopy(img, cr)
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}
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func cropWithCopy(img image.Image, cr image.Rectangle) (image.Image, error) {
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result := image.NewRGBA(cr)
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draw.Draw(result, cr, img, cr.Min, draw.Src)
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return result, nil
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}
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func (c Config) maxBounds(bounds image.Rectangle) (r image.Rectangle) {
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if c.Mode == Centered {
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anchor := c.centeredMin(bounds)
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w := min(anchor.X-bounds.Min.X, bounds.Max.X-anchor.X)
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h := min(anchor.Y-bounds.Min.Y, bounds.Max.Y-anchor.Y)
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r = image.Rect(anchor.X-w, anchor.Y-h, anchor.X+w, anchor.Y+h)
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} else {
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r = image.Rect(c.Anchor.X, c.Anchor.Y, bounds.Max.X, bounds.Max.Y)
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}
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return
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}
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// computeSize retrieve the effective size of the cropped image.
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// It is defined by Height, Width, and Ratio option.
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func (c Config) computeSize(bounds image.Rectangle, ratio image.Point) (p image.Point) {
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if c.Options&Ratio == Ratio {
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// Ratio option is on, so we take the biggest size available that fit the given ratio.
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if float64(ratio.X)/float64(bounds.Dx()) > float64(ratio.Y)/float64(bounds.Dy()) {
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p = image.Point{bounds.Dx(), (bounds.Dx() / ratio.X) * ratio.Y}
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} else {
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p = image.Point{(bounds.Dy() / ratio.Y) * ratio.X, bounds.Dy()}
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}
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} else {
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p = image.Point{ratio.X, ratio.Y}
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}
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return
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}
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// computedCropArea retrieve the theorical crop area.
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// It is defined by Height, Width, Mode and
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func (c Config) computedCropArea(bounds image.Rectangle, size image.Point) (r image.Rectangle) {
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min := bounds.Min
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switch c.Mode {
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case Centered:
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rMin := c.centeredMin(bounds)
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r = image.Rect(rMin.X-size.X/2, rMin.Y-size.Y/2, rMin.X-size.X/2+size.X, rMin.Y-size.Y/2+size.Y)
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default: // TopLeft
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rMin := image.Point{min.X + c.Anchor.X, min.Y + c.Anchor.Y}
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r = image.Rect(rMin.X, rMin.Y, rMin.X+size.X, rMin.Y+size.Y)
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}
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return
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}
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func (c *Config) centeredMin(bounds image.Rectangle) (rMin image.Point) {
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if c.Anchor.X == 0 && c.Anchor.Y == 0 {
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rMin = image.Point{
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X: bounds.Dx() / 2,
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Y: bounds.Dy() / 2,
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}
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} else {
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rMin = image.Point{
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X: c.Anchor.X,
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Y: c.Anchor.Y,
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}
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}
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return
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}
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func min(a, b int) (r int) {
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if a < b {
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r = a
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} else {
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r = b
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}
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return
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}
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