mtsatellite/common/image.go

112 lines
2.2 KiB
Go

// Copyright 2014, 2015 by Sascha L. Teichmann
// Use of this source code is governed by the MIT license
// that can be found in the LICENSE file.
package common
import (
"bufio"
"bytes"
"errors"
"image"
"image/png"
"log"
"os"
"strconv"
"sync"
"time"
"github.com/bamiaux/rez"
)
// ResizeFilter is used to scale down the pyramid tiles.
var ResizeFilter = rez.NewLanczosFilter(3)
var rrand uint32
var rrandmu sync.Mutex
func reseed() uint32 {
return uint32(time.Now().UnixNano() + int64(os.Getpid()))
}
func nextSuffix() string {
rrandmu.Lock()
r := rrand
if r == 0 {
r = reseed()
}
r = r*1664525 + 1013904223 // constants from Numerical Recipes
rrand = r
rrandmu.Unlock()
return strconv.Itoa(int(1e9 + r%1e9))[1:]
}
func EncodeToMem(img image.Image) ([]byte, error) {
var buf bytes.Buffer
enc := png.Encoder{png.BestCompression}
if err := enc.Encode(&buf, img); err != nil {
return nil, err
}
return buf.Bytes(), nil
}
func SaveAsPNG(path string, img image.Image) (err error) {
var file *os.File
if file, err = os.Create(path); err != nil {
return
}
writer := bufio.NewWriter(file)
err = png.Encode(writer, img)
writer.Flush()
file.Close()
return
}
func tmpName(tmpl string) (string, error) {
tmpPre := tmpl + ".tmp"
nconflict := 0
for i := 0; i < 10000; i++ {
tmp := tmpPre + nextSuffix()
if _, err := os.Stat(tmp); err != nil {
if os.IsNotExist(err) {
return tmp, nil
}
return "", err
}
if nconflict++; nconflict > 10 {
nconflict = 0
rrand = reseed()
}
}
return "", errors.New("Cannot create temp name")
}
func SaveAsPNGAtomic(path string, img image.Image) (err error) {
var tmpPath string
if tmpPath, err = tmpName(path); err != nil {
return
}
// Still a bit racy
if err = SaveAsPNG(tmpPath, img); err != nil {
return
}
return os.Rename(tmpPath, path)
}
func LoadPNG(path string) image.Image {
var err error
var file *os.File
if file, err = os.Open(path); err != nil {
return image.White
}
defer file.Close()
reader := bufio.NewReader(file)
var img image.Image
if img, err = png.Decode(reader); err != nil {
log.Printf("WARN: decoding '%s' failed: %s\n", path, err)
return image.White
}
return img
}