77 lines
2.9 KiB
JavaScript
77 lines
2.9 KiB
JavaScript
/**
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* @module ol/geom/flat/textpath
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*/
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import {lerp} from '../../math.js';
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/**
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* @param {Array<number>} flatCoordinates Path to put text on.
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* @param {number} offset Start offset of the `flatCoordinates`.
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* @param {number} end End offset of the `flatCoordinates`.
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* @param {number} stride Stride.
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* @param {string} text Text to place on the path.
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* @param {number} startM m along the path where the text starts.
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* @param {number} maxAngle Max angle between adjacent chars in radians.
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* @param {number} scale The product of the text scale and the device pixel ratio.
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* @param {function(string, string, Object<string, number>):number} measureAndCacheTextWidth Measure and cache text width.
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* @param {string} font The font.
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* @param {Object<string, number>} cache A cache of measured widths.
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* @return {Array<Array<*>>} The result array (or null if `maxAngle` was
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* exceeded). Entries of the array are x, y, anchorX, angle, chunk.
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*/
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export function drawTextOnPath(
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flatCoordinates, offset, end, stride, text, startM, maxAngle, scale, measureAndCacheTextWidth, font, cache) {
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const result = [];
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// Keep text upright
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const reverse = flatCoordinates[offset] > flatCoordinates[end - stride];
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const numChars = text.length;
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let x1 = flatCoordinates[offset];
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let y1 = flatCoordinates[offset + 1];
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offset += stride;
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let x2 = flatCoordinates[offset];
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let y2 = flatCoordinates[offset + 1];
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let segmentM = 0;
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let segmentLength = Math.sqrt(Math.pow(x2 - x1, 2) + Math.pow(y2 - y1, 2));
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let angleChanged = false;
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let index, previousAngle;
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for (let i = 0; i < numChars; ++i) {
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index = reverse ? numChars - i - 1 : i;
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const char = text[index];
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const charLength = scale * measureAndCacheTextWidth(font, char, cache);
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const charM = startM + charLength / 2;
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while (offset < end - stride && segmentM + segmentLength < charM) {
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x1 = x2;
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y1 = y2;
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offset += stride;
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x2 = flatCoordinates[offset];
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y2 = flatCoordinates[offset + 1];
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segmentM += segmentLength;
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segmentLength = Math.sqrt(Math.pow(x2 - x1, 2) + Math.pow(y2 - y1, 2));
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}
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const segmentPos = charM - segmentM;
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let angle = Math.atan2(y2 - y1, x2 - x1);
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if (reverse) {
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angle += angle > 0 ? -Math.PI : Math.PI;
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}
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if (previousAngle !== undefined) {
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let delta = angle - previousAngle;
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angleChanged = angleChanged || delta !== 0;
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delta += (delta > Math.PI) ? -2 * Math.PI : (delta < -Math.PI) ? 2 * Math.PI : 0;
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if (Math.abs(delta) > maxAngle) {
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return null;
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}
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}
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previousAngle = angle;
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const interpolate = segmentPos / segmentLength;
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const x = lerp(x1, x2, interpolate);
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const y = lerp(y1, y2, interpolate);
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result[index] = [x, y, charLength / 2, angle, char];
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startM += charLength;
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}
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return angleChanged ? result : [[result[0][0], result[0][1], result[0][2], result[0][3], text]];
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}
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