private void writeHeader(
String version,
int logicalScreenWidth,
int logicalScreenHeight,
int colorResolution,
int pixelAspectRatio,
int backgroundColorIndex,
boolean sortFlag,
int bitsPerPixel,
byte[] globalColorTable)
throws IOException {
try {
// Signature
stream.writeBytes("GIF" + version);
// Screen Descriptor
// Width
stream.writeShort((short) logicalScreenWidth);
// Height
stream.writeShort((short) logicalScreenHeight);
// Global Color Table
// Packed fields
int packedFields = globalColorTable != null ? 0x80 : 0x00;
packedFields |= ((colorResolution - 1) & 0x7) << 4;
if (sortFlag) {
packedFields |= 0x8;
}
packedFields |= (bitsPerPixel - 1);
stream.write(packedFields);
// Background color index
stream.write(backgroundColorIndex);
// Pixel aspect ratio
stream.write(pixelAspectRatio);
// Global Color Table
if (globalColorTable != null) {
stream.write(globalColorTable);
}
} catch (IOException e) {
throw new IIOException("I/O error writing header!", e);
}
}
