58 lines
1.6 KiB
Java
58 lines
1.6 KiB
Java
package a2geek.apple2.image.encoder.encode;
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import a2geek.apple2.image.encoder.A2Image;
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/**
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* Perform repeated byte packing (really is a type of RLE).
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* <p>
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* Encoding becomes: <code>RR [ XX | RR XX NN ]</code>
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* where:<ul>
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* <li>RR is the repeat toggle byte (1st entry is to identify it).</li>
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* <li>XX is the color byte to place in Apple II memory.</li>
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* <li>NN is the number of bytes repeated.</li>
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* </ul>
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*
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* @author a2geek@users.noreply.github.com
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*/
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public class RleEncoder extends A2Encoder {
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public String getTitle() {
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return "RLE (Standard)";
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}
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public void encode(A2Image a2, int maxSize) {
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byte[] data = a2.getBytes();
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encode(data, maxSize);
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}
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public void encode(byte[] data, int maxSize) {
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reset(maxSize);
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// Identify an unused value:
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int count[] = new int[256];
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for (int i=0; i<data.length; i++) {
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count[data[i] & 0xff]++;
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}
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int repeatByte = 0;
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for (int i=0; i<count.length; i++) {
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if (count[i] == 0) {
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repeatByte = i;
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break;
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}
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}
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// Encode data!
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addByte(repeatByte);
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for (int i=0; i<data.length; i++) {
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int color = data[i] & 0xff;
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if (i < data.length-2 && (color == repeatByte || (color == (data[i+1] & 0xff) && color == (data[i+2] & 0xff)))) {
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int number = 1;
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while (i < data.length-1 && number < 0xff && (data[i+1] & 0xff) == color) {
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number++;
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i++;
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}
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addByte(repeatByte);
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addByte(color);
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addByte(number);
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} else {
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addByte(color);
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}
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}
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}
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}
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