mirror of
https://github.com/Azgaar/Fantasy-Map-Generator.git
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103 lines
No EOL
3.5 KiB
JavaScript
103 lines
No EOL
3.5 KiB
JavaScript
'use strict';
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// lineclip by mourner, https://github.com/mapbox/lineclip
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// Cohen-Sutherland line clippign algorithm, adapted to efficiently
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// handle polylines rather than just segments
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function lineclip(points, bbox, result) {
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var len = points.length,
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codeA = bitCode(points[0], bbox),
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part = [],
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i, a, b, codeB, lastCode;
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if (!result) result = [];
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for (i = 1; i < len; i++) {
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a = points[i - 1];
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b = points[i];
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codeB = lastCode = bitCode(b, bbox);
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while (true) {
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if (!(codeA | codeB)) { // accept
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part.push(a);
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if (codeB !== lastCode) { // segment went outside
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part.push(b);
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if (i < len - 1) { // start a new line
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result.push(part);
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part = [];
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}
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} else if (i === len - 1) {
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part.push(b);
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}
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break;
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} else if (codeA & codeB) { // trivial reject
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break;
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} else if (codeA) { // a outside, intersect with clip edge
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a = intersect(a, b, codeA, bbox);
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codeA = bitCode(a, bbox);
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} else { // b outside
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b = intersect(a, b, codeB, bbox);
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codeB = bitCode(b, bbox);
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}
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}
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codeA = lastCode;
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}
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if (part.length) result.push(part);
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return result;
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}
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// Sutherland-Hodgeman polygon clipping algorithm
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function polygonclip(points, bbox, secure = 0) {
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var result, edge, prev, prevInside, inter, i, p, inside;
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// clip against each side of the clip rectangle
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for (edge = 1; edge <= 8; edge *= 2) {
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result = [];
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prev = points[points.length-1];
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prevInside = !(bitCode(prev, bbox) & edge);
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for (i = 0; i < points.length; i++) {
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p = points[i];
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inside = !(bitCode(p, bbox) & edge);
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inter = inside !== prevInside; // segment goes through the clip window
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const pi = intersect(prev, p, edge, bbox);
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if (inter) result.push(pi); // add an intersection point
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if (secure && inter) result.push(pi, pi); // add additional intersection points to secure correct d3 curve
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if (inside) result.push(p); // add a point if it's inside
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prev = p;
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prevInside = inside;
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}
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points = result;
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if (!points.length) break;
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}
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//result.forEach(p => debug.append("circle").attr("cx", p[0]).attr("cy", p[1]).attr("r", .6).attr("fill", "red"));
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return result;
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}
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// intersect a segment against one of the 4 lines that make up the bbox
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function intersect(a, b, edge, bbox) {
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return edge & 8 ? [a[0] + (b[0] - a[0]) * (bbox[3] - a[1]) / (b[1] - a[1]), bbox[3]] : // top
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edge & 4 ? [a[0] + (b[0] - a[0]) * (bbox[1] - a[1]) / (b[1] - a[1]), bbox[1]] : // bottom
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edge & 2 ? [bbox[2], a[1] + (b[1] - a[1]) * (bbox[2] - a[0]) / (b[0] - a[0])] : // right
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edge & 1 ? [bbox[0], a[1] + (b[1] - a[1]) * (bbox[0] - a[0]) / (b[0] - a[0])] : null; // left
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}
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// bit code reflects the point position relative to the bbox:
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// left mid right
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// top 1001 1000 1010
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// mid 0001 0000 0010
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// bottom 0101 0100 0110
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function bitCode(p, bbox) {
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var code = 0;
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if (p[0] < bbox[0]) code |= 1; // left
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else if (p[0] > bbox[2]) code |= 2; // right
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if (p[1] < bbox[1]) code |= 4; // bottom
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else if (p[1] > bbox[3]) code |= 8; // top
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return code;
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} |