minecraft - decode.go

     1  package maps // import "vimagination.zapto.org/minecraft/maps"
     2  
     3  import (
     4  	"image"
     5  	"io"
     6  
     7  	"vimagination.zapto.org/minecraft/nbt"
     8  )
     9  
    10  func init() {
    11  	image.RegisterFormat("minecraftmap", "\x0a\x00\x00\x0a\x00\x04data", Decode, Config)
    12  }
    13  
    14  func readData(r io.Reader) (nbt.Compound, error) {
    15  	t, err := nbt.Decode(r)
    16  	if err != nil {
    17  		return nil, err
    18  	}
    19  
    20  	if t.TagID() != nbt.TagCompound {
    21  		return nil, nbt.WrongTag{
    22  			Expecting: nbt.TagCompound,
    23  			Got:       t.TagID(),
    24  		}
    25  	}
    26  
    27  	d := t.Data().(nbt.Compound).Get("data")
    28  	if d.TagID() != nbt.TagCompound {
    29  		return nil, nbt.WrongTag{
    30  			Expecting: nbt.TagCompound,
    31  			Got:       d.TagID(),
    32  		}
    33  	}
    34  
    35  	return d.Data().(nbt.Compound), nil
    36  }
    37  
    38  func getDimensions(d nbt.Compound) image.Rectangle {
    39  	var width, height int
    40  
    41  	if w := d.Get("width"); w.TagID() == nbt.TagShort {
    42  		width = int(w.Data().(nbt.Short))
    43  	}
    44  
    45  	if h := d.Get("height"); h.TagID() == nbt.TagShort {
    46  		height = int(h.Data().(nbt.Short))
    47  	}
    48  
    49  	return image.Rectangle{
    50  		image.Point{0, 0},
    51  		image.Point{width, height},
    52  	}
    53  }
    54  
    55  // Decode takes a reader for an uncompressed Minecraft map.
    56  //
    57  // Minecraft maps are gzip compressed, so the reader given to this func should
    58  // be wrapped in gzip.NewReader.
    59  func Decode(r io.Reader) (image.Image, error) {
    60  	d, err := readData(r)
    61  	if err != nil {
    62  		return nil, err
    63  	}
    64  
    65  	c := d.Get("colors")
    66  	if c.TagID() != nbt.TagByteArray {
    67  		return nil, nbt.WrongTag{
    68  			Expecting: nbt.TagByteArray,
    69  			Got:       c.TagID(),
    70  		}
    71  	}
    72  
    73  	rect := getDimensions(d)
    74  
    75  	return &image.Paletted{
    76  		Pix:     c.Data().(nbt.ByteArray).Bytes(),
    77  		Stride:  rect.Max.X,
    78  		Rect:    rect,
    79  		Palette: palette,
    80  	}, nil
    81  }
    82  
    83  // Config reader the configuration for an uncompressed Minecraft map.
    84  //
    85  // Minecraft maps are gzip compressed, so the reader given to this func should
    86  // be wrapped in gzip.NewReader.
    87  func Config(r io.Reader) (image.Config, error) {
    88  	d, err := readData(r)
    89  	if err != nil {
    90  		return image.Config{}, err
    91  	}
    92  
    93  	rect := getDimensions(d)
    94  
    95  	return image.Config{
    96  		ColorModel: palette,
    97  		Width:      int(rect.Max.X),
    98  		Height:     int(rect.Max.Y),
    99  	}, nil
   100  }
   101