void decodePass(int xOffset, int yOffset, int xStep, int yStep, int passWidth, int passHeight) {
if ((passWidth == 0) || (passHeight == 0)) {
return;
}
int bytesPerRow = (inputBands * passWidth * bitDepth + 7) / 8;
byte[] curr = new byte[bytesPerRow];
byte[] prior = new byte[bytesPerRow];
// Decode the (sub)image row-by-row
int srcY, dstY;
for (srcY = 0, dstY = yOffset; srcY < passHeight; srcY++, dstY += yStep) {
// Read the filter type byte and a row of data
int filter = 0;
try {
filter = dataStream.read();
dataStream.readFully(curr, 0, bytesPerRow);
} catch (Exception e) {
// empty on purpose
}
switch (filter) {
case PNG_FILTER_NONE:
break;
case PNG_FILTER_SUB:
decodeSubFilter(curr, bytesPerRow, bytesPerPixel);
break;
case PNG_FILTER_UP:
decodeUpFilter(curr, prior, bytesPerRow);
break;
case PNG_FILTER_AVERAGE:
decodeAverageFilter(curr, prior, bytesPerRow, bytesPerPixel);
break;
case PNG_FILTER_PAETH:
decodePaethFilter(curr, prior, bytesPerRow, bytesPerPixel);
break;
default:
// Error -- uknown filter type
throw new RuntimeException("PNG filter unknown.");
}
processPixels(curr, xOffset, xStep, dstY, passWidth);
// Swap curr and prior
byte[] tmp = prior;
prior = curr;
curr = tmp;
}
}
