Press n or j to go to the next uncovered block, b, p or k for the previous block.
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let paethPredictor = require("./paeth-predictor");
function filterNone(pxData, pxPos, byteWidth, rawData, rawPos) {
for (let x = 0; x < byteWidth; x++) {
rawData[rawPos + x] = pxData[pxPos + x];
}
}
function filterSumNone(pxData, pxPos, byteWidth) {
let sum = 0;
let length = pxPos + byteWidth;
for (let i = pxPos; i < length; i++) {
sum += Math.abs(pxData[i]);
}
return sum;
}
function filterSub(pxData, pxPos, byteWidth, rawData, rawPos, bpp) {
for (let x = 0; x < byteWidth; x++) {
let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
let val = pxData[pxPos + x] - left;
rawData[rawPos + x] = val;
}
}
function filterSumSub(pxData, pxPos, byteWidth, bpp) {
let sum = 0;
for (let x = 0; x < byteWidth; x++) {
let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
let val = pxData[pxPos + x] - left;
sum += Math.abs(val);
}
return sum;
}
function filterUp(pxData, pxPos, byteWidth, rawData, rawPos) {
for (let x = 0; x < byteWidth; x++) {
let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
let val = pxData[pxPos + x] - up;
rawData[rawPos + x] = val;
}
}
function filterSumUp(pxData, pxPos, byteWidth) {
let sum = 0;
let length = pxPos + byteWidth;
for (let x = pxPos; x < length; x++) {
let up = pxPos > 0 ? pxData[x - byteWidth] : 0;
let val = pxData[x] - up;
sum += Math.abs(val);
}
return sum;
}
function filterAvg(pxData, pxPos, byteWidth, rawData, rawPos, bpp) {
for (let x = 0; x < byteWidth; x++) {
let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
let val = pxData[pxPos + x] - ((left + up) >> 1);
rawData[rawPos + x] = val;
}
}
function filterSumAvg(pxData, pxPos, byteWidth, bpp) {
let sum = 0;
for (let x = 0; x < byteWidth; x++) {
let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
let val = pxData[pxPos + x] - ((left + up) >> 1);
sum += Math.abs(val);
}
return sum;
}
function filterPaeth(pxData, pxPos, byteWidth, rawData, rawPos, bpp) {
for (let x = 0; x < byteWidth; x++) {
let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
let upleft =
pxPos > 0 && x >= bpp ? pxData[pxPos + x - (byteWidth + bpp)] : 0;
let val = pxData[pxPos + x] - paethPredictor(left, up, upleft);
rawData[rawPos + x] = val;
}
}
function filterSumPaeth(pxData, pxPos, byteWidth, bpp) {
let sum = 0;
for (let x = 0; x < byteWidth; x++) {
let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
let upleft =
pxPos > 0 && x >= bpp ? pxData[pxPos + x - (byteWidth + bpp)] : 0;
let val = pxData[pxPos + x] - paethPredictor(left, up, upleft);
sum += Math.abs(val);
}
return sum;
}
let filters = {
0: filterNone,
1: filterSub,
2: filterUp,
3: filterAvg,
4: filterPaeth,
};
let filterSums = {
0: filterSumNone,
1: filterSumSub,
2: filterSumUp,
3: filterSumAvg,
4: filterSumPaeth,
};
module.exports = function (pxData, width, height, options, bpp) {
let filterTypes;
Eif (!("filterType" in options) || options.filterType === -1) {
filterTypes = [0, 1, 2, 3, 4];
} else if (typeof options.filterType === "number") {
filterTypes = [options.filterType];
} else {
throw new Error("unrecognised filter types");
}
Iif (options.bitDepth === 16) {
bpp *= 2;
}
let byteWidth = width * bpp;
let rawPos = 0;
let pxPos = 0;
let rawData = Buffer.alloc((byteWidth + 1) * height);
let sel = filterTypes[0];
for (let y = 0; y < height; y++) {
Eif (filterTypes.length > 1) {
// find best filter for this line (with lowest sum of values)
let min = Infinity;
for (let i = 0; i < filterTypes.length; i++) {
let sum = filterSums[filterTypes[i]](pxData, pxPos, byteWidth, bpp);
if (sum < min) {
sel = filterTypes[i];
min = sum;
}
}
}
rawData[rawPos] = sel;
rawPos++;
filters[sel](pxData, pxPos, byteWidth, rawData, rawPos, bpp);
rawPos += byteWidth;
pxPos += byteWidth;
}
return rawData;
};
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