/
thumbnail.go
66 lines (57 loc) · 1.84 KB
/
thumbnail.go
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// Copyright 2022 Google LLC
//
// 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 main
import (
"bytes"
"context"
"image"
"image/png"
"math"
"golang.org/x/image/draw"
"github.com/ServiceWeaver/weaver"
)
type ImageScaler interface {
Scale(_ context.Context, img []byte, maxWidth, maxHeight int) ([]byte, error)
}
// scaler scales an image.
type scaler struct {
weaver.Implements[ImageScaler]
}
// Scale resizes img so it has at most the specified maximum width and height
// while preserving its aspect ratio.
func (s *scaler) Scale(_ context.Context, img []byte, maxWidth, maxHeight int) ([]byte, error) {
src, _, err := image.Decode(bytes.NewBuffer(img))
if err != nil {
return nil, err
}
bounds := src.Bounds()
w := bounds.Max.X - bounds.Min.X
h := bounds.Max.Y - bounds.Min.Y
if w <= maxWidth && h <= maxHeight {
return img, nil
}
// Find the smallest scaling ratio across the two dimensions.
sx := float64(maxWidth) / float64(w)
sy := float64(maxHeight) / float64(h)
ratio := math.Min(sx, sy)
scaledWidth := int(ratio * float64(w))
scaledHeight := int(ratio * float64(h))
dst := image.NewRGBA(image.Rect(0, 0, scaledWidth, scaledHeight))
draw.NearestNeighbor.Scale(dst, dst.Rect, src, src.Bounds(), draw.Over, nil)
var buf bytes.Buffer
if err := png.Encode(&buf, dst); err != nil {
return nil, err
}
return buf.Bytes(), nil
}