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package com.bumptech.glide.gifdecoder.test;
import java.nio.ByteBuffer;
/**
* Utils for writing the bytes of various parts of GIFs to byte buffers.
*/
public class GifBytesTestUtil {
// Length in bytes.
public static final int HEADER_LENGTH = 13;
// Length in bytes.
public static final int IMAGE_DESCRIPTOR_LENGTH = 10;
public static void writeFakeImageData(ByteBuffer out, int lzwMinCodeSize) {
// 1 for lzwMinCodeSize, 1 for length, 1 for min content, 1 for block terminator.
verifyRemaining(out, 4);
verifyShortValues(lzwMinCodeSize);
out.put((byte) lzwMinCodeSize);
// Block length.
out.put((byte) 0x01);
// Block content.
out.put((byte) 0x01);
// End of block.
out.put((byte) 0x00);
}
public static void writeImageDescriptor(ByteBuffer out, int imageLeft, int imageTop, int imageWidth,
int imageHeight) {
verifyRemaining(out, IMAGE_DESCRIPTOR_LENGTH);
verifyShortValues(imageLeft, imageTop, imageWidth, imageHeight);
// Image separator
out.put((byte) 0x2C);
out.putShort((short) imageLeft).putShort((short) imageTop).putShort((short) imageWidth)
.putShort((short) imageHeight);
}
public static void writeHeaderAndLsd(ByteBuffer out, int width, int height, boolean hasGct, int gctSize) {
verifyRemaining(out, HEADER_LENGTH);
verifyShortValues(width, height);
// GIF
out.put((byte) 0x47).put((byte) 0x49).put((byte) 0x46);
// Version - 89a.
out.put((byte) 0x38).put((byte) 0x39).put((byte) 0x61);
/** LSD (Logical Screen Descriptor) **/
// Width.
out.putShort((short) width);
// Height.
out.putShort((short) height);
// Packed GCT (Global Color Table) flag + color resolution + sort flag + size of GCT.
// GCT flag (false) - most significant bit.
byte gctFlag = (byte) ((hasGct ? 1 : 0) << 7);
// Color resolution - next three bits.
byte colorResolution = 1 << 5;
// Sort flag - next bit;
byte sortFlag = 0 << 4;
// exponent of size of color table, size = 2^(1 + exponent) - least significant 3 bits.
byte size = (byte) gctSize;
byte packed = (byte) (gctFlag | colorResolution | sortFlag | size);
out.put(packed);
// Background color index.
out.put((byte) 0);
// Pixel aspect ratio.
out.put((byte) 0);
}
private static void verifyRemaining(ByteBuffer buffer, int expected) {
if (buffer.remaining() < expected) {
throw new IllegalArgumentException("Must have at least " + expected + " bytes to write");
}
}
private static void verifyShortValues(int... shortValues) {
for (int dimen : shortValues) {
if (dimen > Short.MAX_VALUE || dimen < 0) {
throw new IllegalArgumentException("Must pass in non-negative short dimensions, not: " + dimen);
}
}
}
}
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