example_test.go

     1  // Copyright 2016 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package png_test
     6  
     7  import (
     8  	"encoding/base64"
     9  	"fmt"
    10  	"image"
    11  	"image/color"
    12  	"image/png"
    13  	"io"
    14  	"log"
    15  	"os"
    16  	"strings"
    17  )
    18  
    19  const gopher = `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`
    20  
    21  // gopherPNG creates an io.Reader by decoding the base64 encoded image data string in the gopher constant.
    22  func gopherPNG() io.Reader { return base64.NewDecoder(base64.StdEncoding, strings.NewReader(gopher)) }
    23  
    24  func ExampleDecode() {
    25  	// This example uses png.Decode which can only decode PNG images.
    26  	// Consider using the general image.Decode as it can sniff and decode any registered image format.
    27  	img, err := png.Decode(gopherPNG())
    28  	if err != nil {
    29  		log.Fatal(err)
    30  	}
    31  
    32  	levels := []string{" ", "░", "▒", "▓", "█"}
    33  
    34  	for y := img.Bounds().Min.Y; y < img.Bounds().Max.Y; y++ {
    35  		for x := img.Bounds().Min.X; x < img.Bounds().Max.X; x++ {
    36  			c := color.GrayModel.Convert(img.At(x, y)).(color.Gray)
    37  			level := c.Y / 51 // 51 * 5 = 255
    38  			if level == 5 {
    39  				level--
    40  			}
    41  			fmt.Print(levels[level])
    42  		}
    43  		fmt.Print("\n")
    44  	}
    45  }
    46  
    47  func ExampleEncode() {
    48  	const width, height = 256, 256
    49  
    50  	// Create a colored image of the given width and height.
    51  	img := image.NewNRGBA(image.Rect(0, 0, width, height))
    52  
    53  	for y := 0; y < height; y++ {
    54  		for x := 0; x < width; x++ {
    55  			img.Set(x, y, color.NRGBA{
    56  				R: uint8((x + y) & 255),
    57  				G: uint8((x + y) << 1 & 255),
    58  				B: uint8((x + y) << 2 & 255),
    59  				A: 255,
    60  			})
    61  		}
    62  	}
    63  
    64  	f, err := os.Create("image.png")
    65  	if err != nil {
    66  		log.Fatal(err)
    67  	}
    68  
    69  	if err := png.Encode(f, img); err != nil {
    70  		f.Close()
    71  		log.Fatal(err)
    72  	}
    73  
    74  	if err := f.Close(); err != nil {
    75  		log.Fatal(err)
    76  	}
    77  }
    78
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