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let interlaceUtils = require("./interlace");
let paethPredictor = require("./paeth-predictor");
function getByteWidth(width, bpp, depth) {
let byteWidth = width * bpp;
if (depth !== 8) {
byteWidth = Math.ceil(byteWidth / (8 / depth));
}
return byteWidth;
}
let Filter = (module.exports = function (bitmapInfo, dependencies) {
let width = bitmapInfo.width;
let height = bitmapInfo.height;
let interlace = bitmapInfo.interlace;
let bpp = bitmapInfo.bpp;
let depth = bitmapInfo.depth;
this.read = dependencies.read;
this.write = dependencies.write;
this.complete = dependencies.complete;
this._imageIndex = 0;
this._images = [];
if (interlace) {
let passes = interlaceUtils.getImagePasses(width, height);
for (let i = 0; i < passes.length; i++) {
this._images.push({
byteWidth: getByteWidth(passes[i].width, bpp, depth),
height: passes[i].height,
lineIndex: 0,
});
}
} else {
this._images.push({
byteWidth: getByteWidth(width, bpp, depth),
height: height,
lineIndex: 0,
});
}
// when filtering the line we look at the pixel to the left
// the spec also says it is done on a byte level regardless of the number of pixels
// so if the depth is byte compatible (8 or 16) we subtract the bpp in order to compare back
// a pixel rather than just a different byte part. However if we are sub byte, we ignore.
if (depth === 8) {
this._xComparison = bpp;
} else if (depth === 16) {
this._xComparison = bpp * 2;
} else {
this._xComparison = 1;
}
});
Filter.prototype.start = function () {
this.read(
this._images[this._imageIndex].byteWidth + 1,
this._reverseFilterLine.bind(this)
);
};
Filter.prototype._unFilterType1 = function (
rawData,
unfilteredLine,
byteWidth
) {
let xComparison = this._xComparison;
let xBiggerThan = xComparison - 1;
for (let x = 0; x < byteWidth; x++) {
let rawByte = rawData[1 + x];
let f1Left = x > xBiggerThan ? unfilteredLine[x - xComparison] : 0;
unfilteredLine[x] = rawByte + f1Left;
}
};
Filter.prototype._unFilterType2 = function (
rawData,
unfilteredLine,
byteWidth
) {
let lastLine = this._lastLine;
for (let x = 0; x < byteWidth; x++) {
let rawByte = rawData[1 + x];
let f2Up = lastLine ? lastLine[x] : 0;
unfilteredLine[x] = rawByte + f2Up;
}
};
Filter.prototype._unFilterType3 = function (
rawData,
unfilteredLine,
byteWidth
) {
let xComparison = this._xComparison;
let xBiggerThan = xComparison - 1;
let lastLine = this._lastLine;
for (let x = 0; x < byteWidth; x++) {
let rawByte = rawData[1 + x];
let f3Up = lastLine ? lastLine[x] : 0;
let f3Left = x > xBiggerThan ? unfilteredLine[x - xComparison] : 0;
let f3Add = Math.floor((f3Left + f3Up) / 2);
unfilteredLine[x] = rawByte + f3Add;
}
};
Filter.prototype._unFilterType4 = function (
rawData,
unfilteredLine,
byteWidth
) {
let xComparison = this._xComparison;
let xBiggerThan = xComparison - 1;
let lastLine = this._lastLine;
for (let x = 0; x < byteWidth; x++) {
let rawByte = rawData[1 + x];
let f4Up = lastLine ? lastLine[x] : 0;
let f4Left = x > xBiggerThan ? unfilteredLine[x - xComparison] : 0;
let f4UpLeft = x > xBiggerThan && lastLine ? lastLine[x - xComparison] : 0;
let f4Add = paethPredictor(f4Left, f4Up, f4UpLeft);
unfilteredLine[x] = rawByte + f4Add;
}
};
Filter.prototype._reverseFilterLine = function (rawData) {
let filter = rawData[0];
let unfilteredLine;
let currentImage = this._images[this._imageIndex];
let byteWidth = currentImage.byteWidth;
if (filter === 0) {
unfilteredLine = rawData.slice(1, byteWidth + 1);
} else {
unfilteredLine = Buffer.alloc(byteWidth);
switch (filter) {
case 1:
this._unFilterType1(rawData, unfilteredLine, byteWidth);
break;
case 2:
this._unFilterType2(rawData, unfilteredLine, byteWidth);
break;
case 3:
this._unFilterType3(rawData, unfilteredLine, byteWidth);
break;
case 4:
this._unFilterType4(rawData, unfilteredLine, byteWidth);
break;
default:
throw new Error("Unrecognised filter type - " + filter);
}
}
this.write(unfilteredLine);
currentImage.lineIndex++;
if (currentImage.lineIndex >= currentImage.height) {
this._lastLine = null;
this._imageIndex++;
currentImage = this._images[this._imageIndex];
} else {
this._lastLine = unfilteredLine;
}
if (currentImage) {
// read, using the byte width that may be from the new current image
this.read(currentImage.byteWidth + 1, this._reverseFilterLine.bind(this));
} else {
this._lastLine = null;
this.complete();
}
};
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