image-in-browser/lib/formats/webp/webp-filters.js

Package for encoding / decoding images, transforming images, applying filters, drawing primitives on images on the client side (no need for server Node.js)

import { InputBuffer } from '../../common/input-buffer.js';
export class WebPFilters {
    static predictLine(src, pred, dst, length, inverse) {
        if (inverse) {
            for (let i = 0; i < length; ++i)
                dst.set(i, src.get(i) + pred.get(i));
        }
        else {
            for (let i = 0; i < length; ++i)
                dst.set(i, src.get(i) - pred.get(i));
        }
    }
    static doHorizontalFilter(src, width, _height, stride, row, numRows, inverse, _out) {
        let _row = row;
        const startOffset = _row * stride;
        const lastRow = _row + numRows;
        const s = new InputBuffer({ buffer: src, offset: startOffset });
        const o = new InputBuffer({ buffer: src, offset: startOffset });
        const preds = InputBuffer.from(inverse ? o : s);
        if (_row === 0) {
            o.set(0, s.get(0));
            this.predictLine(InputBuffer.from(s, 1), preds, InputBuffer.from(o, 1), width - 1, inverse);
            _row = 1;
            preds.offset += stride;
            s.offset += stride;
            o.offset += stride;
        }
        while (_row < lastRow) {
            this.predictLine(s, InputBuffer.from(preds, -stride), o, 1, inverse);
            this.predictLine(InputBuffer.from(s, 1), preds, InputBuffer.from(o, 1), width - 1, inverse);
            ++_row;
            preds.offset += stride;
            s.offset += stride;
            o.offset += stride;
        }
    }
    static doVerticalFilter(src, width, _height, stride, row, numRows, inverse, out) {
        let _row = row;
        const startOffset = _row * stride;
        const lastRow = _row + numRows;
        const s = new InputBuffer({ buffer: src, offset: startOffset });
        const o = new InputBuffer({ buffer: out, offset: startOffset });
        const preds = InputBuffer.from(inverse ? o : s);
        if (_row === 0) {
            o.set(0, s.get(0));
            this.predictLine(InputBuffer.from(s, 1), preds, InputBuffer.from(o, 1), width - 1, inverse);
            _row = 1;
            s.offset += stride;
            o.offset += stride;
        }
        else {
            preds.offset -= stride;
        }
        while (_row < lastRow) {
            this.predictLine(s, preds, o, width, inverse);
            ++_row;
            preds.offset += stride;
            s.offset += stride;
            o.offset += stride;
        }
    }
    static gradientPredictor(a, b, c) {
        const g = a + b - c;
        return (g & ~0xff) === 0 ? g : g < 0 ? 0 : 255;
    }
    static doGradientFilter(src, width, _height, stride, row, numRows, inverse, out) {
        let _row = row;
        const startOffset = _row * stride;
        const lastRow = _row + numRows;
        const s = new InputBuffer({ buffer: src, offset: startOffset });
        const o = new InputBuffer({ buffer: out, offset: startOffset });
        const preds = InputBuffer.from(inverse ? o : s);
        if (_row === 0) {
            o.set(0, s.get(0));
            this.predictLine(InputBuffer.from(s, 1), preds, InputBuffer.from(o, 1), width - 1, inverse);
            _row = 1;
            preds.offset += stride;
            s.offset += stride;
            o.offset += stride;
        }
        while (_row < lastRow) {
            this.predictLine(s, InputBuffer.from(preds, -stride), o, 1, inverse);
            for (let w = 1; w < width; ++w) {
                const pred = this.gradientPredictor(preds.get(w - 1), preds.get(w - stride), preds.get(w - stride - 1));
                o.set(w, s.get(w) + (inverse ? pred : -pred));
            }
            ++_row;
            preds.offset += stride;
            s.offset += stride;
            o.offset += stride;
        }
    }
    static horizontalFilter(data, width, height, stride, filteredData) {
        WebPFilters.doHorizontalFilter(data, width, height, stride, 0, height, false, filteredData);
    }
    static horizontalUnfilter(width, height, stride, row, numRows, data) {
        WebPFilters.doHorizontalFilter(data, width, height, stride, row, numRows, true, data);
    }
    static verticalFilter(data, width, height, stride, filteredData) {
        WebPFilters.doVerticalFilter(data, width, height, stride, 0, height, false, filteredData);
    }
    static verticalUnfilter(width, height, stride, row, numRows, data) {
        WebPFilters.doVerticalFilter(data, width, height, stride, row, numRows, true, data);
    }
    static gradientFilter(data, width, height, stride, filteredData) {
        WebPFilters.doGradientFilter(data, width, height, stride, 0, height, false, filteredData);
    }
    static gradientUnfilter(width, height, stride, row, numRows, data) {
        WebPFilters.doGradientFilter(data, width, height, stride, row, numRows, true, data);
    }
}
WebPFilters.filterNone = 0;
WebPFilters.filterHorizontal = 1;
WebPFilters.filterVertical = 2;
WebPFilters.filterGradient = 3;
WebPFilters.filterLast = WebPFilters.filterGradient + 1;
WebPFilters.filterBest = 5;
WebPFilters.filterFast = 6;
WebPFilters.filters = [
    undefined,
    WebPFilters.horizontalFilter,
    WebPFilters.verticalFilter,
    WebPFilters.gradientFilter,
];
WebPFilters.unfilters = [
    undefined,
    WebPFilters.horizontalUnfilter,
    WebPFilters.verticalUnfilter,
    WebPFilters.gradientUnfilter,
];
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