pngfileformat.java

源码为Eclipse开源开发平台桌面开发工具SWT的源代码,

void setImageDataValues(byte[] data, ImageData imageData) {
	byte[] result = validateBitDepth(data);
	setPixelData(result, imageData);
}
/**
 * Read the image data from the data stream. This must handle
 * decoding the data, filtering, and interlacing.
 */
void readPixelData(PngIdatChunk chunk, PngChunkReader chunkReader) {
	decodingStream = new PngDecodingDataStream(chunk, chunkReader);
	int interlaceMethod = headerChunk.getInterlaceMethod();
	if (interlaceMethod == PngIhdrChunk.INTERLACE_METHOD_NONE) {
		readNonInterlacedImage();
	} else {
		readInterlacedImage();
	}
	decodingStream.assertImageDataAtEnd();
	decodingStream.checkAdler();
}
/**
 * Answer the number of bytes in a word-aligned row of pixel data.
 */
int getAlignedBytesPerRow() {
	return ((getBytesPerRow(headerChunk.getWidth()) + 3) / 4) * 4;
}
/**
 * Answer the number of bytes in each row of the image
 * data. Each PNG row is byte-aligned, so images with bit
 * depths less than a byte may have unused bits at the
 * end of each row. The value of these bits is undefined.
 */
int getBytesPerRow() {
	return getBytesPerRow(headerChunk.getWidth());
}
/**
 * Answer the number of bytes needed to represent a pixel.
 * This value depends on the image's color type and bit
 * depth. 
 * Note that this method rounds up if an image's pixel size
 * isn't byte-aligned.
 */
int getBytesPerPixel() {
	int bitsPerPixel = headerChunk.getBitsPerPixel();
	return (bitsPerPixel + 7) / 8;	
}
/**
 * Answer the number of bytes in a row of the given pixel
 * width. Each row is byte-aligned, so images with bit
 * depths less than a byte may have unused bits at the
 * end of each row. The value of these bits is undefined.
 */
int getBytesPerRow(int rowWidthInPixels) {
	int bitsPerPixel = headerChunk.getBitsPerPixel();
	int bitsPerRow = bitsPerPixel * rowWidthInPixels;
	int bitsPerByte = 8;
	return (bitsPerRow + (bitsPerByte - 1)) / bitsPerByte;
}
/**
 * 1. Read one of the seven frames of interlaced data.
 * 2. Update the imageData.
 * 3. Notify the image loader's listeners of the frame load.
 */
void readInterlaceFrame(
	int rowInterval,
	int columnInterval,
	int startRow,
	int startColumn,
	int frameCount) 
{
	int width = headerChunk.getWidth();
	int alignedBytesPerRow = getAlignedBytesPerRow();
	int height = headerChunk.getHeight();
	if (startRow >= height || startColumn >= width) return;
	
	int pixelsPerRow = (width - startColumn + columnInterval - 1) / columnInterval;
	int bytesPerRow = getBytesPerRow(pixelsPerRow);
	byte[] row1 = new byte[bytesPerRow];
	byte[] row2 = new byte[bytesPerRow];
	byte[] currentRow = row1;	
	byte[] lastRow = row2;	
	for (int row = startRow; row < height; row += rowInterval) {
		byte filterType = decodingStream.getNextDecodedByte();
		for (int col = 0; col < bytesPerRow; col++) {
			currentRow[col] = decodingStream.getNextDecodedByte();
		}
		filterRow(currentRow, lastRow, filterType);
		if (headerChunk.getBitDepth() >= 8) {
			int bytesPerPixel = getBytesPerPixel();
			int dataOffset = (row * alignedBytesPerRow) + (startColumn * bytesPerPixel);
			for (int rowOffset = 0; rowOffset < currentRow.length; rowOffset += bytesPerPixel) {
				for (int byteOffset = 0; byteOffset < bytesPerPixel; byteOffset++) {
					data[dataOffset + byteOffset] = currentRow[rowOffset + byteOffset];
				}
				dataOffset += (columnInterval * bytesPerPixel);
			}
		} else {
			int bitsPerPixel = headerChunk.getBitDepth();
			int pixelsPerByte = 8 / bitsPerPixel;
			int column = startColumn;
			int rowBase = row * alignedBytesPerRow;
			int valueMask = 0;
			for (int i = 0; i < bitsPerPixel; i++) {
				valueMask <<= 1;
				valueMask |= 1;
			}
			int maxShift = 8 - bitsPerPixel;
			for (int byteOffset = 0; byteOffset < currentRow.length; byteOffset++) {
				for (int bitOffset = maxShift; bitOffset >= 0; bitOffset -= bitsPerPixel) {
					if (column < width) {
						int dataOffset = rowBase + (column * bitsPerPixel / 8);							
						int value = (currentRow[byteOffset] >> bitOffset) & valueMask;
						int dataShift = maxShift - (bitsPerPixel * (column % pixelsPerByte));
						data[dataOffset] |= value << dataShift;
					}
					column += columnInterval;
				}
			}
		}
		currentRow = (currentRow == row1) ? row2 : row1;
		lastRow = (lastRow == row1) ? row2 : row1;
	}
	setImageDataValues(data, imageData);
	fireInterlacedFrameEvent(frameCount);
}
/**
 * Read the pixel data for an interlaced image from the
 * data stream.
 */
void readInterlacedImage() {
	readInterlaceFrame(8, 8, 0, 0, 0);
	readInterlaceFrame(8, 8, 0, 4, 1);	
	readInterlaceFrame(8, 4, 4, 0, 2);	
	readInterlaceFrame(4, 4, 0, 2, 3);
	readInterlaceFrame(4, 2, 2, 0, 4);
	readInterlaceFrame(2, 2, 0, 1, 5);	
	readInterlaceFrame(2, 1, 1, 0, 6);
}
/**
 * Fire an event to let listeners know that an interlaced
 * frame has been loaded.
 * finalFrame should be true if the image has finished
 * loading, false if there are more frames to come.
 */
void fireInterlacedFrameEvent(int frameCount) {
	if (loader.hasListeners()) {
		ImageData image = (ImageData) imageData.clone();
		boolean finalFrame = frameCount == 6;
		loader.notifyListeners(new ImageLoaderEvent(loader, image, frameCount, finalFrame));
	}
}
/**
 * Read the pixel data for a non-interlaced image from the
 * data stream.
 * Update the imageData to reflect the new data.
 */
void readNonInterlacedImage() {
	int dataOffset = 0;
	int alignedBytesPerRow = getAlignedBytesPerRow();
	int bytesPerRow = getBytesPerRow();
	byte[] row1 = new byte[bytesPerRow];
	byte[] row2 = new byte[bytesPerRow];
	byte[] currentRow = row1;	
	byte[] lastRow = row2;
	for (int row = 0; row < headerChunk.getHeight(); row++) {
		byte filterType = decodingStream.getNextDecodedByte();
		for (int col = 0; col < bytesPerRow; col++) {
			currentRow[col] = decodingStream.getNextDecodedByte();
		}
		filterRow(currentRow, lastRow, filterType);
		System.arraycopy(currentRow, 0, data, dataOffset, bytesPerRow);
		dataOffset += alignedBytesPerRow;
		currentRow = (currentRow == row1) ? row2 : row1;
		lastRow = (lastRow == row1) ? row2 : row1;
	}
	setImageDataValues(data, imageData);
}
/**
 * SWT does not support 16-bit depth color formats.
 * Convert the 16-bit data to 8-bit data.
 * The correct way to do this is to multiply each
 * 16 bit value by the value:
 * (2^8 - 1) / (2^16 - 1).
 * The fast way to do this is just to drop the low
 * byte of the 16-bit value.
 */
static void compress16BitDepthTo8BitDepth(
	byte[] source,
	int sourceOffset,
	byte[] destination, 
	int destinationOffset,
	int numberOfValues) 
{
	//double multiplier = (Compatibility.pow2(8) - 1) / (Compatibility.pow2(16) - 1);
	for (int i = 0; i < numberOfValues; i++) {
		int sourceIndex = sourceOffset + (2 * i);
		int destinationIndex = destinationOffset + i;
		//int value = (source[sourceIndex] << 8) | source[sourceIndex + 1];
		//byte compressedValue = (byte)(value * multiplier);
		byte compressedValue = source[sourceIndex];
		destination[destinationIndex] = compressedValue;
	}
}
/**
 * SWT does not support 16-bit depth color formats.
 * Convert the 16-bit data to 8-bit data.
 * The correct way to do this is to multiply each
 * 16 bit value by the value:
 * (2^8 - 1) / (2^16 - 1).
 * The fast way to do this is just to drop the low
 * byte of the 16-bit value.
 */
static int compress16BitDepthTo8BitDepth(int value) {
	//double multiplier = (Compatibility.pow2(8) - 1) / (Compatibility.pow2(16) - 1);
	//byte compressedValue = (byte)(value * multiplier);
	return value >> 8;
}
/**
 * PNG supports four filtering types. These types are applied
 * per row of image data. This method unfilters the given row
 * based on the filterType.
 */
void filterRow(byte[] row, byte[] previousRow, int filterType) {
	int byteOffset = headerChunk.getFilterByteOffset();
	switch (filterType) {
		case PngIhdrChunk.FILTER_NONE:
			break;
		case PngIhdrChunk.FILTER_SUB:
			for (int i = byteOffset; i < row.length; i++) {
				int current = row[i] & 0xFF;
				int left = row[i - byteOffset] & 0xFF;
				row[i] = (byte)((current + left) & 0xFF);
			}
			break;
		case PngIhdrChunk.FILTER_UP:
			for (int i = 0; i < row.length; i++) {
				int current = row[i] & 0xFF;
				int above = previousRow[i] & 0xFF;				
				row[i] = (byte)((current + above) & 0xFF);
			}
			break;
		case PngIhdrChunk.FILTER_AVERAGE:
			for (int i = 0; i < row.length; i++) {
				int left = (i < byteOffset) ? 0 : row[i - byteOffset] & 0xFF;
				int above = previousRow[i] & 0xFF;
				int current = row[i] & 0xFF;
				row[i] = (byte)((current + ((left + above) / 2)) & 0xFF);
			}
			break;
		case PngIhdrChunk.FILTER_PAETH:
			for (int i = 0; i < row.length; i++) {
				int left = (i < byteOffset) ? 0 : row[i - byteOffset] & 0xFF;
				int aboveLeft = (i < byteOffset) ? 0 : previousRow[i - byteOffset] & 0xFF;
				int above = previousRow[i] & 0xFF;
				
				int a = Math.abs(above - aboveLeft);
				int b = Math.abs(left - aboveLeft);
				int c = Math.abs(left - aboveLeft + above - aboveLeft);
				
				int preductor = 0;
				if (a <= b && a <= c) {
					preductor = left;
				} else if (b <= c) {
					preductor = above;
				} else {
					preductor = aboveLeft;
				}
				
				int currentValue = row[i] & 0xFF;
				row[i] = (byte) ((currentValue + preductor) & 0xFF);
			}
			break;
	}
}

}