minecraft - maps/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  	return d.Data().(nbt.Compound), nil
    35  }
    36  
    37  func getDimensions(d nbt.Compound) image.Rectangle {
    38  	var width, height int
    39  	w := d.Get("width")
    40  	if w.TagID() == nbt.TagShort {
    41  		width = int(w.Data().(nbt.Short))
    42  	}
    43  	h := d.Get("height")
    44  	if h.TagID() == nbt.TagShort {
    45  		height = int(h.Data().(nbt.Short))
    46  	}
    47  	return image.Rectangle{
    48  		image.Point{0, 0},
    49  		image.Point{width, height},
    50  	}
    51  }
    52  
    53  // Decode takes a reader for an uncompressed Minecraft map.
    54  //
    55  // Minecraft maps are gzip compressed, so the reader given to this func should
    56  // be wrapped in gzip.NewReader.
    57  func Decode(r io.Reader) (image.Image, error) {
    58  	d, err := readData(r)
    59  	if err != nil {
    60  		return nil, err
    61  	}
    62  
    63  	c := d.Get("colors")
    64  	if c.TagID() != nbt.TagByteArray {
    65  		return nil, nbt.WrongTag{
    66  			Expecting: nbt.TagByteArray,
    67  			Got:       c.TagID(),
    68  		}
    69  	}
    70  
    71  	rect := getDimensions(d)
    72  
    73  	return &image.Paletted{
    74  		Pix:     c.Data().(nbt.ByteArray).Bytes(),
    75  		Stride:  rect.Max.X,
    76  		Rect:    rect,
    77  		Palette: palette,
    78  	}, nil
    79  }
    80  
    81  // Config reader the configuration for an uncompressed Minecraft map.
    82  //
    83  // Minecraft maps are gzip compressed, so the reader given to this func should
    84  // be wrapped in gzip.NewReader.
    85  func Config(r io.Reader) (image.Config, error) {
    86  	d, err := readData(r)
    87  	if err != nil {
    88  		return image.Config{}, err
    89  	}
    90  	rect := getDimensions(d)
    91  	return image.Config{
    92  		ColorModel: palette,
    93  		Width:      int(rect.Max.X),
    94  		Height:     int(rect.Max.Y),
    95  	}, nil
    96  }
    97