8bit archeology returns

While working on Märchen Maze translation I checked if other Namcot games use the same image encoding format. It appears that not only some Namcot games use it but there are Pack-In-Video games as well. Maybe the same subcontractor studio was involved.
Anyway, here is the list of the games I checked so far.

• Märchen Maze
• Obocchama Kun
• World Jockey
• Zipang

The encoding is pretty simple. The image is split in 32 bytes blocs. Each bloc can be encoded using one of he following 4 techniques :

0. 0 filled : the bloc is filled with 0. A plain old memset is enough.

   1	memset(out, 0, 32)

1. Sparse : the bloc contains 0 bytes. The first 4 bytes indicates if the corresponding bloc byte is 0 or read from the data buffer.

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   uint8_t *input; // pointer to encoded input data. uint8_t *out;   // pointer to output data. // ... // sparse_decode int i, j; uint8_t *header = input; uint8_t *data   = input+4; uint8_t  bit; for(i=0; i<4; i++) {     bit = header[i];     for(j=0; j<8; j++)     {         *out++ = (bit & 1) ? *data++ : 0x00;         bit >>= 1;     } }

2. XOR Sparse : Just like the “sparse” encoding but the bloc was previously processed using a sequence of xor on each consecutive 16 bytes in order to increase the number of 0 in the bloc.

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   sparse_decode(out, input); // xor for(i=0; i<16; i+=2) {     out[i+0x02] ^= out[i+0x00];     out[i+0x03] ^= out[i+0x01];     out[i+0x12] ^= out[i+0x10];     out[i+0x13] ^= out[i+0x11]; }

3. Raw : the bloc data is stored unencoded, just call

   1	memcpy(out, data, 32)

The encoding type is packed in 4 bits stored separately from the image data. This means that a byte stores the encoding type for 4 blocs.

The pseudo code for the whole decoding routine looks like this.

• Source code for Märchen Maze, Obocchama Kun and Zipang.
• Source code for World Jockey.