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