More .obj investigating. 0x80 seems to be a special value

internal/data/object.go

@@ -1,7 +1,7 @@
 package data
 
 import (
-	"bytes"
+	"bufio"
 	"encoding/binary"
 	"fmt"
 	"io"
@@ -36,7 +36,7 @@ func (s SpriteHeader) Check(expectedSize uint32) error {
 type Sprite struct {
 	SpriteHeader
 
-	PixelData []byte
+	Rows [][]byte
 }
 
 type dirEntry struct {
@@ -113,27 +113,18 @@ func LoadObject(filename string) (*Object, error) {
 		return nil, err
 	}
 
-	// FIXME: this might - *might* - load interstitial data we don't really
-	// need, so wasting memory.
-	data, err := ioutil.ReadAll(f)
-	if err != nil {
-		return nil, err
-	}
-
-	buf := bytes.NewReader(data)
-
 	for _, dirEntry := range dir {
 		if err := dirEntry.Check(); err != nil {
 			return nil, err
 		}
 
-		if _, err := buf.Seek(int64(dirEntry.Offset), io.SeekStart); err != nil {
+		if _, err := f.Seek(int64(out.DataOffset+dirEntry.Offset), io.SeekStart); err != nil {
 			return nil, err
 		}
 
 		sprite := &Sprite{}
 
-		if err := binary.Read(buf, binary.LittleEndian, &sprite.SpriteHeader); err != nil {
+		if err := binary.Read(f, binary.LittleEndian, &sprite.SpriteHeader); err != nil {
 			return nil, err
 		}
 
@@ -141,11 +132,18 @@ func LoadObject(filename string) (*Object, error) {
 			return nil, err
 		}
 
-		// It's safe to assume that a `bytes.Reader` will always satisfy the
-		// requested read size.
-		sprite.PixelData = make([]byte, sprite.PixelSize)
-		if _, err := buf.Read(sprite.PixelData); err != nil {
-			return nil, err
+		// The pixeldata seems to be formed of Y null-terminated records, with
+		// varying numbers of bytes in each row. I don't know the internal
+		// structure yet, but there's definitely working pixel data in there
+		buf := bufio.NewReader(io.LimitReader(f, int64(sprite.PixelSize)))
+		sprite.Rows = make([][]byte, sprite.Height)
+
+		for y := 0; y < int(sprite.Height); y++ {
+			if row, err := buf.ReadBytes(0x00); err != nil {
+				return nil, err
+			} else {
+				sprite.Rows[y] = row
+			}
 		}
 
 		out.Sprites = append(out.Sprites, sprite)