1 | // License: GPL. For details, see LICENSE file.
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2 | package org.openstreetmap.josm.data.osm.visitor.paint;
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3 |
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4 | import static java.awt.geom.Rectangle2D.OUT_BOTTOM;
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5 | import static java.awt.geom.Rectangle2D.OUT_LEFT;
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6 | import static java.awt.geom.Rectangle2D.OUT_RIGHT;
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7 | import static java.awt.geom.Rectangle2D.OUT_TOP;
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8 |
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9 | import java.awt.Point;
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10 | import java.awt.Rectangle;
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11 |
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12 | /**
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13 | * Computes the part of a line that is visible in a given rectangle.
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14 | * Using int leads to overflow, so we need long int.
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15 | */
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16 | public class LineClip {
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17 | private Point p1, p2;
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18 | private final Rectangle clipBounds;
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19 |
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20 | public LineClip(Point p1, Point p2, Rectangle clipBounds) {
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21 | this.p1 = p1;
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22 | this.p2 = p2;
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23 | this.clipBounds = clipBounds;
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24 | }
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25 |
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26 | /**
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27 | * run the clipping algorithm
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28 | * @return true if the some parts of the line lies within the clip bounds
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29 | */
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30 | public boolean execute() {
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31 | return cohenSutherland(p1.x, p1.y, p2.x, p2.y, clipBounds.x , clipBounds.y, clipBounds.x + clipBounds.width, clipBounds.y + clipBounds.height);
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32 | }
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33 |
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34 | /**
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35 | * @return start point of the clipped line
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36 | */
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37 | public Point getP1()
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38 | {
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39 | return p1;
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40 | }
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41 |
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42 | /**
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43 | * @return end point of the clipped line
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44 | */
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45 | public Point getP2() {
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46 | return p2;
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47 | }
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48 |
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49 | /**
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50 | * Cohen–Sutherland algorithm.
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51 | * See <a href="https://en.wikipedia.org/wiki/Cohen%E2%80%93Sutherland_algorithm">Wikipedia article</a>
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52 | * @return true, if line is visible in the given clip region
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53 | */
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54 | private boolean cohenSutherland( long x1, long y1, long x2, long y2, long xmin, long ymin, long xmax, long ymax) {
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55 | int outcode0, outcode1, outcodeOut;
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56 | boolean accept = false;
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57 | boolean done = false;
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58 |
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59 | outcode0 = computeOutCode (x1, y1, xmin, ymin, xmax, ymax);
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60 | outcode1 = computeOutCode (x2, y2, xmin, ymin, xmax, ymax);
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61 |
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62 | do {
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63 | if ((outcode0 | outcode1) == 0 ) {
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64 | accept = true;
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65 | done = true;
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66 | }
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67 | else if ( (outcode0 & outcode1) > 0 ) {
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68 | done = true;
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69 | }
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70 | else {
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71 | long x = 0, y = 0;
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72 | outcodeOut = outcode0 != 0 ? outcode0: outcode1;
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73 | if ( (outcodeOut & OUT_TOP) > 0 ) {
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74 | x = x1 + (x2 - x1) * (ymax - y1)/(y2 - y1);
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75 | y = ymax;
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76 | }
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77 | else if ((outcodeOut & OUT_BOTTOM) > 0 ) {
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78 | x = x1 + (x2 - x1) * (ymin - y1)/(y2 - y1);
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79 | y = ymin;
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80 | }
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81 | else if ((outcodeOut & OUT_RIGHT)> 0) {
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82 | y = y1 + (y2 - y1) * (xmax - x1)/(x2 - x1);
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83 | x = xmax;
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84 | }
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85 | else if ((outcodeOut & OUT_LEFT) > 0) {
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86 | y = y1 + (y2 - y1) * (xmin - x1)/(x2 - x1);
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87 | x = xmin;
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88 | }
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89 | if (outcodeOut == outcode0) {
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90 | x1 = x;
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91 | y1 = y;
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92 | outcode0 = computeOutCode(x1, y1, xmin, ymin, xmax, ymax);
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93 | } else {
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94 | x2 = x;
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95 | y2 = y;
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96 | outcode1 = computeOutCode(x2, y2, xmin, ymin, xmax, ymax);
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97 | }
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98 | }
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99 | }
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100 | while (!done);
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101 |
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102 | if(accept) {
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103 | p1 = new Point((int) x1, (int) y1);
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104 | p2 = new Point((int) x2, (int) y2);
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105 | return true;
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106 | }
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107 | return false;
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108 | }
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109 |
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110 | /**
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111 | * The outcode of the point.
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112 | * We cannot use Rectangle.outcode since it does not work with long ints.
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113 | */
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114 | private static int computeOutCode (long x, long y, long xmin, long ymin, long xmax, long ymax) {
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115 | int code = 0;
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116 | if (y > ymax) {
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117 | code |= OUT_TOP;
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118 | }
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119 | else if (y < ymin) {
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120 | code |= OUT_BOTTOM;
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121 | }
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122 | if (x > xmax) {
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123 | code |= OUT_RIGHT;
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124 | }
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125 | else if (x < xmin) {
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126 | code |= OUT_LEFT;
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127 | }
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128 | return code;
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129 | }
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130 | }
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