001 // License: GPL. For details, see LICENSE file.
002 package org.openstreetmap.josm.data.osm.visitor.paint;
003
004 import static java.awt.geom.Rectangle2D.OUT_LEFT;
005 import static java.awt.geom.Rectangle2D.OUT_RIGHT;
006 import static java.awt.geom.Rectangle2D.OUT_TOP;
007 import static java.awt.geom.Rectangle2D.OUT_BOTTOM;
008 import java.awt.Point;
009 import java.awt.Rectangle;
010
011 /**
012 * Computes the part of a line that is visible in a given rectangle.
013 * Using int leads to overflow, so we need long int.
014 */
015 public class LineClip {
016 private Point p1, p2;
017 private final Rectangle clipBounds;
018
019 public LineClip(Point p1, Point p2, Rectangle clipBounds) {
020 this.p1 = p1;
021 this.p2 = p2;
022 this.clipBounds = clipBounds;
023 }
024
025 /**
026 * run the clipping algorithm
027 * @return true if the some parts of the line lies within the clip bounds
028 */
029 public boolean execute() {
030 return cohenSutherland(p1.x, p1.y, p2.x, p2.y, clipBounds.x , clipBounds.y, clipBounds.x + clipBounds.width, clipBounds.y + clipBounds.height);
031 }
032
033 /**
034 * @return start point of the clipped line
035 */
036 public Point getP1()
037 {
038 return p1;
039 }
040
041 /**
042 * @return end point of the clipped line
043 */
044 public Point getP2()
045 {
046 return p2;
047 }
048
049 /**
050 * see http://en.wikipedia.org/wiki/Cohen-Sutherland
051 * @return true, if line is visible in the given clip region
052 */
053 private boolean cohenSutherland( long x1, long y1, long x2, long y2, long xmin, long ymin, long xmax, long ymax)
054 {
055 int outcode0, outcode1, outcodeOut;
056 boolean accept = false;
057 boolean done = false;
058
059 outcode0 = computeOutCode (x1, y1, xmin, ymin, xmax, ymax);
060 outcode1 = computeOutCode (x2, y2, xmin, ymin, xmax, ymax);
061
062 do {
063 if ((outcode0 | outcode1) == 0 ) {
064 accept = true;
065 done = true;
066 }
067 else if ( (outcode0 & outcode1) > 0 ) {
068 done = true;
069 }
070 else {
071 long x = 0, y = 0;
072 outcodeOut = outcode0 != 0 ? outcode0: outcode1;
073 if ( (outcodeOut & OUT_TOP) > 0 ) {
074 x = x1 + (x2 - x1) * (ymax - y1)/(y2 - y1);
075 y = ymax;
076 }
077 else if ((outcodeOut & OUT_BOTTOM) > 0 ) {
078 x = x1 + (x2 - x1) * (ymin - y1)/(y2 - y1);
079 y = ymin;
080 }
081 else if ((outcodeOut & OUT_RIGHT)> 0) {
082 y = y1 + (y2 - y1) * (xmax - x1)/(x2 - x1);
083 x = xmax;
084 }
085 else if ((outcodeOut & OUT_LEFT) > 0) {
086 y = y1 + (y2 - y1) * (xmin - x1)/(x2 - x1);
087 x = xmin;
088 }
089 if (outcodeOut == outcode0) {
090 x1 = x;
091 y1 = y;
092 outcode0 = computeOutCode(x1, y1, xmin, ymin, xmax, ymax);
093 } else {
094 x2 = x;
095 y2 = y;
096 outcode1 = computeOutCode(x2, y2, xmin, ymin, xmax, ymax);
097 }
098 }
099 }
100 while (!done);
101
102 if(accept) {
103 p1 = new Point((int) x1, (int) y1);
104 p2 = new Point((int) x2, (int) y2);
105 return true;
106 }
107 return false;
108 }
109
110 /**
111 * The outcode of the point.
112 * We cannot use Rectangle.outcode since it does not work with long ints.
113 */
114 private static int computeOutCode (long x, long y, long xmin, long ymin, long xmax, long ymax) {
115 int code = 0;
116 if (y > ymax) {
117 code |= OUT_TOP;
118 }
119 else if (y < ymin) {
120 code |= OUT_BOTTOM;
121 }
122 if (x > xmax) {
123 code |= OUT_RIGHT;
124 }
125 else if (x < xmin) {
126 code |= OUT_LEFT;
127 }
128 return code;
129 }
130 }