112 lines
3.2 KiB
Go
112 lines
3.2 KiB
Go
|
// Package collage composes poster collage images from multiple source images.
|
|||
|
|
package collage
|
|||
|
|
|
|||
|
|
import (
|
|||
|
|
"bytes"
|
|||
|
|
"errors"
|
|||
|
|
"image"
|
|||
|
|
"image/color"
|
|||
|
|
"image/jpeg"
|
|||
|
|
_ "image/png"
|
|||
|
|
|
|||
|
|
"golang.org/x/image/draw"
|
|||
|
|
_ "golang.org/x/image/webp"
|
|||
|
|
)
|
|||
|
|
|
|||
|
|
// ErrNotEnoughImages is returned when no source images are usable.
|
|||
|
|
var ErrNotEnoughImages = errors.New("collage: no usable source images")
|
|||
|
|
|
|||
|
|
const (
|
|||
|
|
posterWidth = 600
|
|||
|
|
posterHeight = 900
|
|||
|
|
jpegQuality = 92
|
|||
|
|
)
|
|||
|
|
|
|||
|
|
// ComposePoster builds a poster collage from raw image bytes.
|
|||
|
|
// Returns JPEG bytes suitable for feeding into processCollectionImage.
|
|||
|
|
//
|
|||
|
|
// Layout:
|
|||
|
|
// - 1 image: scale-fill the full canvas
|
|||
|
|
// - 2-3 images: 2 side-by-side columns
|
|||
|
|
// - 4+ images: 2×2 grid (first 4 used)
|
|||
|
|
func ComposePoster(images [][]byte) ([]byte, error) {
|
|||
|
|
decoded := make([]image.Image, 0, len(images))
|
|||
|
|
for _, data := range images {
|
|||
|
|
img, _, err := image.Decode(bytes.NewReader(data))
|
|||
|
|
if err != nil {
|
|||
|
|
continue
|
|||
|
|
}
|
|||
|
|
decoded = append(decoded, img)
|
|||
|
|
}
|
|||
|
|
if len(decoded) == 0 {
|
|||
|
|
return nil, ErrNotEnoughImages
|
|||
|
|
}
|
|||
|
|
if len(decoded) > 4 {
|
|||
|
|
decoded = decoded[:4]
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
canvas := image.NewNRGBA(image.Rect(0, 0, posterWidth, posterHeight))
|
|||
|
|
|
|||
|
|
// Fill with dark background in case images don't cover fully.
|
|||
|
|
for y := range posterHeight {
|
|||
|
|
for x := range posterWidth {
|
|||
|
|
canvas.SetNRGBA(x, y, color.NRGBA{R: 24, G: 24, B: 27, A: 255})
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
switch len(decoded) {
|
|||
|
|
case 1:
|
|||
|
|
scaleFill(canvas, decoded[0], image.Rect(0, 0, posterWidth, posterHeight))
|
|||
|
|
case 2, 3:
|
|||
|
|
halfW := posterWidth / 2
|
|||
|
|
scaleFill(canvas, decoded[0], image.Rect(0, 0, halfW, posterHeight))
|
|||
|
|
scaleFill(canvas, decoded[1], image.Rect(halfW, 0, posterWidth, posterHeight))
|
|||
|
|
default:
|
|||
|
|
halfW := posterWidth / 2
|
|||
|
|
halfH := posterHeight / 2
|
|||
|
|
scaleFill(canvas, decoded[0], image.Rect(0, 0, halfW, halfH))
|
|||
|
|
scaleFill(canvas, decoded[1], image.Rect(halfW, 0, posterWidth, halfH))
|
|||
|
|
scaleFill(canvas, decoded[2], image.Rect(0, halfH, halfW, posterHeight))
|
|||
|
|
scaleFill(canvas, decoded[3], image.Rect(halfW, halfH, posterWidth, posterHeight))
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
var buf bytes.Buffer
|
|||
|
|
if err := jpeg.Encode(&buf, canvas, &jpeg.Options{Quality: jpegQuality}); err != nil {
|
|||
|
|
return nil, err
|
|||
|
|
}
|
|||
|
|
return buf.Bytes(), nil
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
// scaleFill scales src to cover dst completely (crop-to-fill), centering the
|
|||
|
|
// source image so excess is cropped equally from both sides.
|
|||
|
|
func scaleFill(dst *image.NRGBA, src image.Image, rect image.Rectangle) {
|
|||
|
|
dstW := rect.Dx()
|
|||
|
|
dstH := rect.Dy()
|
|||
|
|
srcBounds := src.Bounds()
|
|||
|
|
srcW := srcBounds.Dx()
|
|||
|
|
srcH := srcBounds.Dy()
|
|||
|
|
|
|||
|
|
// Compute scale factor to cover the destination rectangle.
|
|||
|
|
scaleX := float64(dstW) / float64(srcW)
|
|||
|
|
scaleY := float64(dstH) / float64(srcH)
|
|||
|
|
scale := scaleX
|
|||
|
|
if scaleY > scaleX {
|
|||
|
|
scale = scaleY
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
// Scaled source dimensions.
|
|||
|
|
scaledW := int(float64(srcW) * scale)
|
|||
|
|
scaledH := int(float64(srcH) * scale)
|
|||
|
|
|
|||
|
|
// Compute crop offset to center.
|
|||
|
|
offsetX := (scaledW - dstW) / 2
|
|||
|
|
offsetY := (scaledH - dstH) / 2
|
|||
|
|
|
|||
|
|
// Scale the full source into a temporary image, then copy the centered region.
|
|||
|
|
tmp := image.NewNRGBA(image.Rect(0, 0, scaledW, scaledH))
|
|||
|
|
draw.BiLinear.Scale(tmp, tmp.Bounds(), src, srcBounds, draw.Over, nil)
|
|||
|
|
|
|||
|
|
// Copy the centered crop into the destination rectangle.
|
|||
|
|
draw.Copy(dst, rect.Min, tmp, image.Rect(offsetX, offsetY, offsetX+dstW, offsetY+dstH), draw.Over, nil)
|
|||
|
|
}
|