84 lines
2.9 KiB
JavaScript
84 lines
2.9 KiB
JavaScript
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/**
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* Alignment pattern are fixed reference pattern in defined positions
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* in a matrix symbology, which enables the decode software to re-synchronise
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* the coordinate mapping of the image modules in the event of moderate amounts
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* of distortion of the image.
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*
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* Alignment patterns are present only in QR Code symbols of version 2 or larger
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* and their number depends on the symbol version.
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*/
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const getSymbolSize = require('./utils').getSymbolSize
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/**
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* Calculate the row/column coordinates of the center module of each alignment pattern
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* for the specified QR Code version.
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*
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* The alignment patterns are positioned symmetrically on either side of the diagonal
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* running from the top left corner of the symbol to the bottom right corner.
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*
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* Since positions are simmetrical only half of the coordinates are returned.
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* Each item of the array will represent in turn the x and y coordinate.
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* @see {@link getPositions}
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*
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* @param {Number} version QR Code version
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* @return {Array} Array of coordinate
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*/
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exports.getRowColCoords = function getRowColCoords (version) {
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if (version === 1) return []
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const posCount = Math.floor(version / 7) + 2
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const size = getSymbolSize(version)
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const intervals = size === 145 ? 26 : Math.ceil((size - 13) / (2 * posCount - 2)) * 2
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const positions = [size - 7] // Last coord is always (size - 7)
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for (let i = 1; i < posCount - 1; i++) {
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positions[i] = positions[i - 1] - intervals
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}
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positions.push(6) // First coord is always 6
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return positions.reverse()
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}
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/**
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* Returns an array containing the positions of each alignment pattern.
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* Each array's element represent the center point of the pattern as (x, y) coordinates
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*
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* Coordinates are calculated expanding the row/column coordinates returned by {@link getRowColCoords}
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* and filtering out the items that overlaps with finder pattern
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*
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* @example
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* For a Version 7 symbol {@link getRowColCoords} returns values 6, 22 and 38.
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* The alignment patterns, therefore, are to be centered on (row, column)
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* positions (6,22), (22,6), (22,22), (22,38), (38,22), (38,38).
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* Note that the coordinates (6,6), (6,38), (38,6) are occupied by finder patterns
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* and are not therefore used for alignment patterns.
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*
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* let pos = getPositions(7)
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* // [[6,22], [22,6], [22,22], [22,38], [38,22], [38,38]]
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*
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* @param {Number} version QR Code version
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* @return {Array} Array of coordinates
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*/
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exports.getPositions = function getPositions (version) {
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const coords = []
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const pos = exports.getRowColCoords(version)
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const posLength = pos.length
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for (let i = 0; i < posLength; i++) {
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for (let j = 0; j < posLength; j++) {
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// Skip if position is occupied by finder patterns
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if ((i === 0 && j === 0) || // top-left
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(i === 0 && j === posLength - 1) || // bottom-left
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(i === posLength - 1 && j === 0)) { // top-right
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continue
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}
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coords.push([pos[i], pos[j]])
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}
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}
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return coords
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}
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